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In this article, for the first time, we propose a transformer network-based reinforcement learning (RL) method for power distribution network (PDN) optimization of high bandwidth memory (HBM). The proposed method can provide an optimal decoupling capacitor (decap) design to maximize the reduction of PDN self- and transfer impedances seen at multiple ports. An attention-based transformer network is implemented to directly parameterize decap optimization policy. The optimality performance is significantly improved since the attention mechanism has powerful expression to explore massive combinatorial space for decap assignments. Moreover, it can capture sequential relationships between the decap assignments. The computing time for optimization is dramatically reduced due to the reusable network on the positions of probing ports and decap assignment candidates. This is because the transformer network has a context embedding process to capture meta-features including probing ports positions. In addition, the network is trained with randomly generated datasets. The computing time for training and data cost are critically decreased due to the scalability of the network. Due to its shared weight property and the context embedding process, the network can adapt to a larger scale of problems without additional training. For verification, the results are compared with conventional genetic algorithm (GA), random search (RS), and all the previous RL-based methods. As a result, the proposed method outperforms in all the following aspects: optimality performance, computing time, and data efficiency. [ABSTRACT FROM AUTHOR]

This work presents a 28/38 GHz dual-band power amplifier (PA) for fifth-generation (5G) communication. In this work, a T-topology-matching network is proposed at the output for its dual-band operation and low insertion loss. Also, a modified dual-LC tank-matching method is proposed for the input and interstage part due to its wideband performance and large-impedance transformation capability. This modified dual-LC tank boosts the transformation ratio to 30 at the interstage matching without trading bandwidth for the 28/38 GHz operation. Furthermore, circular inductors are applied to the matching networks for low insertion loss. This design is fabricated in a 0.25- $\mu \text{m}$ SiGe:C BiCMOS technology with a core area of 300 $\times 770\,\,\mu \text{m}^{2}$. In combination with the proposed methods, this PA achieves 28/38 GHz dual-band operation with high power-added efficiency (PAE). At 28 GHz, the measured peak power-added efficiency (PAE $_{\mathrm {peak}}$) is 25%, the saturated output power ($P_{\mathrm {sat}}$) is 18.8 dBm, and 1-dB compressed power ($P_{\mathrm {1~dB}}$) is 17.8 dBm. At 38 GHz, those are 17.5%, 17 dBm, and 15.8 dBm, respectively. [ABSTRACT FROM AUTHOR]

This article proposes a novel concept of an optically invisible artificial magnetic conductor subarrays for bandwidth improvement of display-integrated antennas in millimeter-wave spectrums. The proposed subarrays consist of two unit-cell types that are arranged as $4 \times 4$ super cells to cover target bands of a slotted dipole antenna with triband resonances. The optical transparency is realized by using thin-metal meshes, and both solid and thin-metal mesh prototypes are fabricated to demonstrate the proposed concept from antenna characteristics standpoints. The mesh prototype exhibits the measured 10-dB matching bandwidth of 25.9% at 28.2 GHz with an average gain of 1.12 dBi, which is similar to 21.1% at 27.5 GHz and 1.25 dBi of the simulated results. These results confirm that the proposed concept is feasible to broaden bandwidths of the triband antenna, while maintaining the optical transparency of 85.1%. [ABSTRACT FROM AUTHOR]

A wideband planar multilayer filtering magic-T is proposed and developed. The proposed magic-T uses coupled microstrip slotlines (CMSs) and microstrip-slot transitions. With the orthogonality of even and odd modes of the CMS, the Chebyshev filtering responses of both the in-phase divider part (H-T) and out-of-phase divider part (E-T) are independent of each other. The microstrip-slot transitions act as a part of filtering structures to realize vertical transmission of energy. With equivalent impedance transformer models, the synthesis processes of a four-pole Chebyshev filtering H-T and a three-pole Chebyshev filtering E-T are derived and analyzed. To verify the proposed concept, a prototype with an operating center frequency of 3 GHz, a 100% equal ripple fractional bandwidth, and a different H-T and E-T in-band ripple are synthesized and implemented on a three-layer printed circuit board. The synthesized, simulated, and measured results show good agreements among them, verifying the feasibility of the proposed planar magic-T. [ABSTRACT FROM AUTHOR]

A new class of wideband unequal power divider with enhanced power dividing ratio, fully matching bandwidth, and filtering performance is presented. A leading triple-mode resonator is inserted in front of the power dividing junction to relax the requirement of high impedance and bring in more poles in input return loss (RL) response and isolation response. Therefore, the power dividing ratio is significantly enhanced and bandwidths of input RL and isolation are enlarged. Moreover, the cascade of the leading triple-mode resonator and the following transmission line segments corporately construct Chebyshev filtering performance. Thus, the power divider can be synthesized by the required bandwidth of RL and power dividing ratio. Examples of 4:1 and 8:1 filtering power dividers operating at 2.4 GHz are designed and fabricated. The measured power dividing ratios of two filtering power dividers are 3.8:1 and 8.1:1 with corresponding RL bandwidths of 95.8% and 97.5% ($\vert S_{11}\vert < -10$ dB), and the measured port-to-port isolation bandwidths are 100% ($\vert S_{32}\vert < -14$ dB) and 100% ($\vert S_{32}\vert < -20$ dB), respectively. [ABSTRACT FROM AUTHOR]

In this article, a novel training set optimization method in an artificial neural network (ANN) constructed for high bandwidth interconnects design is proposed based on rigorous probability analysis. In general, the accuracy of an ANN is enhanced by increasing training set size. However, generating large training sets is inevitably time-consuming and resource-demanding, and sometimes even impossible due to limited prototypes or measurement scenarios. Especially, when the number of channels in required design are huge such as graphics double data rate (GDDR) memory and high bandwidth memory (HBM). Therefore, optimizing the training set selection process is crucial to minimizing the training datasets for developing an efficient ANN. According to rigorous mathematical analysis of the uniformity of the training data by probability distribution function, optimization flow of the range selection is proposed to improve accuracy and efficiency. The optimal number of training data samples is further determined by studying the prediction error rates. The performance of the proposed method in terms of accuracy is validated by comparing the scattering parameters of arbitrarily chosen strip and microstrip type GDDR interconnects obtained from EM simulations with those predicted by ANNs using default and the proposed training-set selection methods. [ABSTRACT FROM AUTHOR]

In this article, a new class of tunable filters and diplexers operating in $X$ -band is presented. The proposed circuits are based on an in-line dual-post resonator, which consists of a pair of antipodal partial-height posts. The resonance and coupling characteristics of the proposed resonator can be regulated by the height and height difference of the posts. The most interesting feature of using the in-line dual-post resonator is that the input–output coupling and inter-resonator coupling are inversely proportional to the frequency within the tuning range, which is necessary for maintaining the fixed absolute bandwidth of the tunable filter. A prototype tunable filter is designed and fabricated, showing a low variation ($< \pm 3.9$ %) in the absolute bandwidth over a relatively wide tuning range of about 17%. The waveguide $H$ -plane static $Y$ -junction is designed and cascaded with two channel filters to implement the tunable diplexer. Noncontiguous and contiguous frequency plans can be realized by properly arranging the frequency band of the two channel filters. Measured results show that the tunable diplexer can obtain constant frequency spacing and approximately 10% tuning range with an insertion loss of less than 1.5 dB. [ABSTRACT FROM AUTHOR]

Highly oversized mode converters are the critical devices for high power millimeter-wave transmission systems, characterizing high power capacity and low loss. In order to improve the conversion efficiency from TE01 to TE11 mode, the mode coupling mechanism of oversized elliptical waveguides is explored, and an optimal ellipticity interval to obtain the high conversion efficiency is deduced by analyzing the mode coupling capacity. Considering that ellipticity can affect the power capacity, breakdown thresholds of different operating modes in elliptical waveguides are studied. Based on the analyses, a synthesis method to design the elliptical mode converter integrating the mode conversion efficiency and the power capacity is proposed. A highly oversized mode converter working in $W$ -band is designed, and the simulation results demonstrate that the mode converter achieves the high conversion efficiency over 95% in a relative bandwidth of 19.6%. In order to validate the design, a prototype of the mode converter is fabricated, and the high purity of outputted TE11 mode is verified by the measurement. The oversized mode converter designed by the proposed synthesis method features high efficiency, broad bandwidth, and high power capacity, enabling its full utilization of the potential of gyrotron traveling-wave tubes (gyro-TWTs). [ABSTRACT FROM AUTHOR]

This article presents an $L$ - and $C$ -band radiometer with integrated wideband active hot and cold loads (AHCLs). By seamlessly integrating the distributed low noise amplifying unit and the wideband power-combining unit, the operational bandwidth of the conventional AHCL is significantly enhanced. The proposed distributed AHCL based on the reused noise-generation structure can realize a balanced calibration of the Dicke radiometer in 156% fractional bandwidth and, therefore, results in a significant reduction of noise equivalent temperature difference (NETD). The dual-band radiometer consists of a distributed AHCL, an SPDT switch, an LNA stage, a reflectionless bandpass filter, a diplexer, $L$ - and $C$ -band detectors, and backend analog circuits. Utilizing a distributed AHCL with 156% fractional bandwidth, the achieved NETDs in $L$ - and $C$ -bands are 1.39 K and 0.36 K, respectively. The implemented radiometer demonstrates an ability to make a balanced calibration automatically in an input range from around 225 K to 650 K. To the best of our knowledge, the proposed dual-band radiometer with a distributed AHCL demonstrates the ability to enhance the Dicke radiometer’s sensitivity effectively in the largest fractional bandwidth. [ABSTRACT FROM AUTHOR]

This article presents a novel waveform engineered sequential load modulated balanced amplifier (W-SLMBA) that uses a continuous Class-F−1 control amplifier (CA) to manipulate the impedance trajectory of the balanced amplifier (BA). It is demonstrated that the use of the continuous Class-F−1 CA can trigger a unique impedance load modulation mechanism by which the fundamental impedance of the BA is shaped by the varying second-harmonic load reactance of the CA. Theoretical derivations reveal that this special load modulation yields extended design space for the LMBA, in which high efficiency can be achieved over wide bandwidth and output power back-off (OPBO). A prototype operating from 1.80 to 2.75 GHz is designed following the proposed theory. The implemented LMBA achieves a measured drain efficiency (DE) of 60.2%–68.3% at saturation and 51.8%–69.0% at 8-dB OPBO. When tested with a 100-MHz long-term evolution (LTE) signal having peak-to-average power ratio (PAPR) of 8 dB, the proposed LMBA achieves 50.2%–59.1% average DE and better than −45.1-dBc adjacent channel power ratio (ACPR) across the target bandwidth after digital predistortion (DPD). [ABSTRACT FROM AUTHOR]

In this study, wideband Doherty power amplifiers (DPAs) based on converters comprising one transformer and two capacitors are investigated. Moreover, the parallel and series-type Doherty combiners are investigated. The series-type Doherty combiner is shown to have wider characteristics than the parallel-type converter-based Doherty combiner via numerical analysis. An approximate analysis was applied to the series-type combiner, and a quasi-optimum design parameter was derived for wideband matching. A quasi-optimum design parameter was compared with a true optimum solution derived by numerical analysis, and its certainty was verified. A combiner with parameters close to the true optimum solution was designed and evaluated. A DPA fabricated using this combiner was adequately small for a 5G mobile handset and could be operated in the frequency range of 2.2–2.7 GHz with efficiency exceeding 35% and a sufficiently low distortion under an amplifying wideband modulated signal [fractional bandwidth (FBW): 4% = 0.1/2.5 GHz]. The proposed combiner and its design techniques helped in designing a compact and long battery life of 5G mobile phones with high data throughput at a few gigahertz frequency ranges. [ABSTRACT FROM AUTHOR]

A novel memory-grouped method is proposed for digital predistortion (DPD) of power amplifiers (PAs) with constrained acquisition bandwidth (BW) and extremely low sampling rate. By grouping the basis functions with different memory delays, a two-step algorithm can reduce overfitting in the constrained-BW technique. As a result, excellent DPD performance can be achieved even when the acquisition BW is constrained to several times narrower than the BW of the original input signal. Thus, using the memory-grouped method, a very low-speed analog-to-digital converter (ADC) can be used to sample the constrained feedback signal without aliasing, significantly reducing the cost of configuring a high-speed ADC. The performance of the proposed method is compared with the existing methods in different scenarios. Experimental results show that when the feedback BW is less than the BW of the original input signal, the proposed method can still achieve good performance, while the traditional methods fail to work. The experiment results also imply that the memory-grouped method can reduce the sampling rate by more than ten times. [ABSTRACT FROM AUTHOR]

An under-sampling digital predistortion based on a multi-tone mixing feedback technique (MTM-DPD) is presented in this article. In contrast to the under-sampling digital predistortion (DPD) based on conventional receivers, the proposed method could simultaneously reduce the sampling rate and acquisition bandwidth using a multi-tone mixing (MTM)-based feedback channel. The MTM-DPD is implemented with an evolved direct learning architecture, where the coefficients of a predistorter are estimated based on the aliased feedback signal, preprocessed input signal, and preprocessed kernels of the DPD model. To preprocess the input signal and kernels, the behavioral model of the MTM-based feedback channel and its corresponding identification algorithm are analyzed in detailed. Experimental results show that for a gallium nitride (GaN)-based power amplifier (PA) with 40-MHz input, under the excitation of a 17 tone LO signal with frequency interval 7.68 MHz, the MTM-DPD with sampling rate 15.36 MSPS and acquisition bandwidth 15.36 MHz could improve the adjacent channel power ratio (ACPR) from −30.1 to −46.5 dBc and the error vector magnitude (EVM) from 9.13% to 1.76%. Compared with the conventional full sampling DPD (FS-DPD), the MTM-DPD could reduce the cost of analog-to-digital converters (ADCs) in feedback channel significantly while maintaining satisfactory linearization performance. [ABSTRACT FROM AUTHOR]

This article presents a wideband ultralinear fully integrated power amplifier (PA) in 22-nm fully-depleted silicon-on-insulator (FD-SOI) technology for phased array-based $E$ -band backhaul networks. A novel amplitude to phase modulation (AMPM) compensation technique called NP (N-type P-type) matrix is presented. The performance of the proposed amplifier compared to a traditional N-type common-source (CS) PA is demonstrated in simulation across the corners and wide frequency range. The proposed PA occupies 0.084 mm2 core area and achieves peak 13.1-/13.7-dB gain, 61.8–83.7 GHz (21.9 GHz) 3-dB small signal bandwidth with 0.8 V/1 V supply. At 78 GHz, 13.8-/15.4-dBm peak saturated output power ($P_{\text {SAT}}$) with 13.1%/17% PAE from 0.8 V/1 V supply is measured, respectively. AMPM distortion at the output referred 1-dB compression point ($\text{OP}_{\text {1dB}}$) is less than 3.6° from 65 to 90 GHz. It achieves 18-/24-Gbit/s data rate with 10.7-/8.5-dBm average output power and 8%/4.9% average PAE at 73 GHz with 64/256 QAM modulation and a 0.8-V supply. [ABSTRACT FROM AUTHOR]

The azimuthally rippled cavity for a large-orbit, coharmonic gyro-multiplier, designed to operate at the second and fourth harmonics, at frequencies of 37.5 and 75 GHz, respectively, has been numerically and experimentally confirmed to be insensitive to the polarization of quadrupole, ${\text{TE}}_{2,n}$ -like modes, including the second-harmonic operating mode of the multiplier, a cylindrical TE2,2-like waveguide mode. To test the cavity with this mode required the design, construction, and measurement of ripple wall mode converters, converting the cylindrical TE2,1 mode into the TE2,2 mode. These were designed to operate at a central frequency of ~37.9 GHz, with predicted mode purity of better than 85%, and 3-dB bandwidth of 161 MHz. The constructed converter had a central operating frequency of 37.7 GHz, with $S$ -parameter measurements used to infer suitable mode purity and an operational 3-dB bandwidth of 50 MHz. This has allowed far-field phase measurements of the corrugated cavity to be conducted, where the orientation of the geometry to the polarization of both the TE2,1 and TE2,2 modes was shown to have no effect on the dispersion. [ABSTRACT FROM AUTHOR]

Emerging applications in D-band (110–170GHz) demand amplifiers with high gain-bandwidth (GBW) products. In this frequency range, the cascode stage offers superior available gain, thanks to the high output impedance, but the design of the output matching network entails a GBW tradeoff. The issue is deeply investigated in this work. Simple, closed-form equations for gain and bandwidth as a function of the load reflection coefficient are derived, leading to the following design insights: 1) for maximum gain and bandwidth, the output matching network should be implemented with positive (magnetic) reactances; 2) with lossy reactances, an optimal load reflection coefficient exists to maximize the power gain, ${\Gamma '_{L-{\mathrm{ opt}}}}$ ; and 3) by selecting ${\Gamma '_{L} < \Gamma '_{L-{\mathrm{ opt}}}}$ , the bandwidth increases quickly with a marginal gain penalty, finally enhancing the GBW product. Leveraging the results of the analysis, single-stage and multistage stagger-tuned amplifiers are implemented in SiGe BiCMOS technology. Two- and three-stage amplifiers demonstrate more than 60GHz bandwidth with 20 and 28dB gain, respectively, corresponding to 700GHz and 1.7 THz GBW. Normalizing gain and bandwidth to the number of stages and technology $f_{\max }$ , the resulting figure of merit is remarkably higher than previously reported silicon amplifiers in the same band. [ABSTRACT FROM AUTHOR]

A reconfigurable balanced dual-band bandpass filter (BPF) with constant differential-mode (DM) absolute bandwidth (ABW) and high selectivity is designed in this article. The proposed BPF is composed of a set of asymmetric short stub-loaded resonators (A-SSLRs) and balanced microstrip-to-slotline transition structures (MSTSs). Four varactor diodes are employed to achieve the reconfigurable characteristics with small insertion losses. By changing the coupling distances and selecting the positions of the loaded varactor diodes on A-SSLRs, the DM coupling coefficients $K_{i}$ and quality factors $Q_{i}$ of the proposed BPF can be easily controlled to keep a constant DM ABW. In the overall tuning range, a superior common-mode (CM) suppression is achieved intrinsically, and the DM responses are independent of the CM ones. Furthermore, five DM transmission zeros (TZs) are generated by the mixed-coupling and source–load coupling, which can improve the selectivity obviously. Compared with the published reconfigurable balanced BPFs, the proposed one has the advantages of constant DM ABW, smaller insertion losses, and more independent control on the two DM passbands. In order to validate the design strategies, a prototype circuit is designed, fabricated, and measured. The simulated and measured results are presented with a good agreement to verify the theory and design. [ABSTRACT FROM AUTHOR]

This article presents a dual-mode power divider (PD) that offers new working mechanism, compact size, significant design freedom, wide working bandwidth, arbitrary power division, and ultrawide isolation between the two output ports. The structure is simple in comparison with conventional Wilkinson PDs in that only two composite right-and left-handed (CRLH) transmission lines (TLs) grounded through two resistors are used. Different from previous CRLH-TL-embedded studies in that almost all CRLH-TLs operate at quarter-wavelength phase responses, in the present work, the zero-degree property is noted and used to modify the impedance variation curves. Additionally, because of the use of grounded resistors, the proposed PD can operate in two modes, such that when high-value resistors are used, the PD operates in a lossless mode, while when low-value resistors are used, the PD operates in an attenuated mode. Because working power has been significantly improved due to progress in modern RF system development, more attenuation elements are required. This means that attenuated PDs will become very useful in the future. For verification, two PDs operating in different working modes and power divisions are designed and fabricated. Based on the experimental results, both PDs demonstrate good performance over more than 60% of the bandwidth with reference to the 15-dB S11, ultrawide isolation, full port matching, and compact size. [ABSTRACT FROM AUTHOR]

This article presents a 7-bit wideband passive attenuator with low insertion loss (IL) and high attenuation accuracy in 55-nm CMOS technology. The π-type and bridge-T-type attenuation units utilize an effective capacitive compensation technique, whose bandwidth extension mechanism is detailed in a single-unit pole–zero analysis. The matching-induced performance deterioration is investigated to minimize amplitude and phase errors at the chip level. The fabricated attenuator demonstrates a 32.4-dB attenuation range with a 0.255-dB resolution and a 3.5–8.4-dB IL from dc to 32 GHz. The measured root-mean-square (rms) amplitude and phase errors are below 0.32 dB and 5.33°, respectively. The attenuator occupies a 0.054-mm2 core area and consumes negligible power. [ABSTRACT FROM AUTHOR]

A novel slow wave (SW) substrate-integrated waveguide (SIW) with enhanced SW factor (SWF) and broadened bandwidth is proposed by simultaneously increasing the effective permeability and permittivity. The effective permittivity is increased by the enhanced capacitance between the top plane of the waveguide and the loaded patches which are shorted to the SIW bottom plane by the blind via-holes. The effective permeability is increased by lengthening the current path by adding patches on the blind via-holes. The proposed SW-SIW with simultaneous increased effective permeability and permittivity has two obvious advantages over the reported SW-SIW with only effective permeability or permittivity increased: 1) smaller longitudinal and lateral dimensions resulted from higher SWF and lower cutoff frequency, respectively, and 2) wider bandwidth due to stable wave impedance along the periodical SW structure. The lateral dimension of the proposed SW-SIW is decreased by 53% compared with the normal SIW with the same cutoff frequency. The phase velocity is decreased by 73%, which means the longitudinal length is reduced by 73% consequently. The operation band is 7.0–18.8 GHz (91.5% fractional bandwidth) covering X- and Ku-bands. A prototype of the proposed SW-SIW is manufactured and measured, and the measured results agree well with the simulations. [ABSTRACT FROM AUTHOR]

A wideband low-noise amplifier (LNA) featuring transformer-based wideband input matching is proposed for millimeter-wave applications. By analyzing the properties of conventional series input matching networks, which were widely employed in narrowband LNAs and shunt–series matching networks for bandwidth extension, a novel input matching network possessing the merits of both was proposed. For further bandwidth extension, another peak of input impedance at a higher frequency is introduced for the proposed input matching network. Moreover, it is proved that the proposed input matching network can suppress the gate resistor noise, resulting in significant noise figure (NF) improvement of an LNA. On the other hand, the NF is further reduced by connecting a transformer between the two amplification stages, which helps suppress the noise contribution from the second stage, leading to an LNA design with NF lower than 4.5 dB over a very wide operating bandwidth. To enhance the gain bandwidth, the peak distribution, including both shunt peaking and series peaking, is discussed. By appropriately distributing these peaks, which is also known as the pole-tuning technique, a wider gain bandwidth can be obtained. To validate the proposed techniques, an LNA with two common-source (CS) stages is designed and fabricated using a 65-nm CMOS process, and the overall chip size, including all pads, is only 0.26 mm2. The two CS stages are cascoded for dc biasing to reduce the power consumption. Experimental results show that a peak gain of 13.5 dB is achieved within a −3-dB bandwidth from 19.2 to 42.6 GHz. The measured NF is 3.1–4.5 dB, and the input 1-dB gain compression point (IP1 dB) ranges from −13.54 to −9.89 dBm in the entire gain bandwidth. The input return loss $S_{11}$ is less than −10 dB over a frequency range of 16.8–38.9 GHz. Moreover, benefiting from the current-reuse technique, the power consumption of the LNA is only 6.36 mW. [ABSTRACT FROM AUTHOR]

Substrate-integrated waveguide (SIW) filtering crossovers featuring wide-stopband characteristics and flexibly allocated center frequencies (CFs) and bandwidths (BWs) for two intersecting channels are presented and studied. The development is devised upon a scheme of an over-mode dual-mode substrate-integrated rectangular cavity (SIRC) coupled with multiple single-mode cavities. First, by exploiting the orthogonal TE102 and TE201 modes in the dual-mode SIRC, cross transmission and acceptable isolation can be obtained and implemented for the dual channels. Furthermore, by controlling the resonant frequencies and mutual couplings of the coupled cavities accordingly, especially the over-mode dual-mode SIRC, both the CFs and BWs of the two channels can be allocated flexibly. In addition, by incorporating three kinds of intrinsic spurious-mode suppression techniques, namely, the harmonic staggered technique, centered coupling windows, and offset centered feeding ports, wide-stopband characteristics can be achieved intrinsically and uniquely. Four practical design examples, including fifth-order direct-coupled and fifth-order cross-coupled SIW filtering crossovers with identical channel CFs and BWs, a third-order crossover with the same channel CFs but different channel BWs and another third-order case with different channel CFs but the same channel BWs are synthesized, designed, fabricated, and tested to demonstrate and validate the proposed collaborative design concepts. [ABSTRACT FROM AUTHOR]

A broadband SiGe power amplifier (PA) with double gain peaks for 5G applications is presented. The differential structure is widely adopted in millimeter-wave circuit design to decrease the impact of the source parasitic inductance that is induced by the bonding wires. Since differential PA results in a higher impedance transformation ratio of the matching network, differential PAs generally have narrower bandwidth than single-ended PAs. Through the bandwidth analysis of the matching network, the transformer used for interstage matching is elaborately designed to ease gain fluctuations. By controlling the stationary points of impedance transformation, the maximum available gain characteristic of a transistor, which decreases with increasing frequency, can be compensated. The gain curve of PA, thus, has double gain peaks within operational frequencies to make its frequency responses as flat as possible. The proposed PA for the frequency band from 27 to 37 GHz is fabricated in a standard 130-nm SiGe BiCMOS process, which occupies 0.36 mm2. Under the 2.5-V voltage supply, the SiGe PA exhibited a power gain of 33.5 dB and output power of 21.3 dBm with 24% power-added efficiency at 31 GHz. It achieves a 34% 3-dB small-signal S21 bandwidth from 27.3 to 38.5 GHz. [ABSTRACT FROM AUTHOR]

A Y-junction circulator based on the ridge gap waveguide (RGW) as a hosting guiding structure is designed using a developed closed-form systematic procedure. To validate the structure, an air-filled-to-dielectric-filled transition is proposed using a substrate perforation technique. The proposed RGW circulator covers the whole Ku-band with a matching bandwidth throughout the operational bandwidth below −15 dB. A prototype is fabricated and tested, providing a satisfactory agreement with the simulated results. [ABSTRACT FROM AUTHOR]

This article presents a novel methodology for designing a broadband Doherty power amplifier (DPA) with extended output power back-off (OBO) range. A modified load modulation network (LMN) is proposed to enhance the OBO range and the bandwidth of the DPA simultaneously. Analysis is conducted to explore the relationship between the proposed LMN parameters and the broadband performance under various OBO levels. Generalized design formulas of the LMN parameters are then introduced to offer the broadband solution for arbitrary current ratios and OBO levels. An asymmetric DPA is demonstrated and implemented with gallium nitride (GaN) transistors using the proposed approach. The fabricated DPA operates from 1.4 to 2.5 GHz with 9-dB OBO range. The measured drain efficiency reaches 61%–75.5% at saturation and 44.6%–54.6% at 9-dB OBO within the operating bandwidth. When driven by a 60-MHz modulated signal with 9-dB peak-to-average power ratio (PAPR), the fabricated DPA attains 47.4%–53.5% average drain efficiency and better than −45.5-dBc adjacent channel leakage ratio (ACLR) after digital predistortion. [ABSTRACT FROM AUTHOR]

A newly calibrated testbed based on a commercial vector network analyzer (VNA) is proposed for the fast in-band vector signal characterization and linearization of nonlinear multiport devices. The testbed can acquire both CW and wideband modulated periodic signals without breaking contact with the DUT, in up to five channels. The time-domain measurements are made possible by calibrating all the receivers in the frequency domain. This calibration provides a phase and amplitude correction for the modulation tones of all the incident and reflected waves in the acquisition bandwidth. The measurement bandwidth is determined at calibration by the bandwidth of the periodic OFDM signals used as a phase standard. It is independent of the VNA receivers’ bandwidth. A 500-MHz 100 000-tones 64-QAM OFDM constellation is recovered with 0.48% error vector magnitude (EVM). As an application, a dual-input hybrid Doherty-outphasing power amplifier (HD-OPA) is characterized at 2.08 GHz. A CW signal is used to determine the outphasing angle and input power levels, which provides the best drain and power-added efficiencies for each output power. The dynamic response of the dual-input HD-OPA is acquired on five channels by using the same testbed. Various periodic OFDM signals, with 24 000 tones, are measured before and after predistortion linearization in a fraction of a second. [ABSTRACT FROM AUTHOR]

This article reports on the theory and application of a high-speed Marx generator (HSMG) circuit to realize supply modulation (SM). In order to achieve high-modulation bandwidth, the supply modulator complexity is kept low, enabling multilevel SM with four discrete voltage levels. A prototype is designed and fabricated on a four-layer FR4 board. The efficiency of the proposed modulator is measured with passive loads, achieving 89% at the 5-MHz switching frequency. Applied to a power amplifier (PA), the modulator demonstrates an error vector magnitude (EVM) of 2.64% at 10-MHz switching frequency with a four-ASK signal. Finally, the HSMG is utilized in an innovative mixerless transmitter architecture. Its capabilities are validated at the center frequency of 3.5 GHz for different modulation bandwidths from 2 up to 70 MHz and different constellation schemes—16 QAM, 32 QAM, and 64 QAM. EVM of 5.88% at 10-MHz bandwidth with 64 QAM is obtained without digital predistortion (DPD). [ABSTRACT FROM AUTHOR]

This article presents a new load-modulation power amplifier (PA) architecture—asymmetrical load-modulated balanced amplifier (ALMBA). It is for the first time discovered that the control amplifier (CA) of LMBA can be designed with arbitrary load modulation (LM) ratio by offsetting the symmetry of two sub-amplifiers (BA1 and BA2) in the balanced topology. The rigorous analytical derivation reveals a unification of the quadrature-coupler-based LM PA theory, which inclusively covers the recently reported LMBA within this generalized framework. Through pseudo-Doherty (PD) biasing of the asymmetric BA1 & BA2 (peaking) and the CA (carrier) combined with proper amplitude and phase controls, the optimal LM behaviors of three amplifiers can be achieved independently overextended power back-off range and ultrawide RF bandwidth. Importantly, the LM of CA effectively mitigates the over-driving issue imposed on symmetrical PD-LMBA, leading to enhanced overall reliability and linearity. Based on the proposed theory, an RF-input PD-ALMBA is designed and implemented using commercial GaN transistors. The developed prototype experimentally demonstrates dual-octave bandwidth from 0.55 to 2.2 GHz, which is the widest bandwidth ever reported for load-modulation PAs. The measurement exhibits an efficiency of 49–82% for peak output power and 40–64% for 10-dB OBO within the design bandwidth. When stimulated by a 20-MHz long-term evolution (LTE) signal with 10.5-dB peak to average power ratio (PAPR), an average efficiency of 47–63% is measured over the entire bandwidth at an average output power around 33 dBm. [ABSTRACT FROM AUTHOR]

The increasing need to improve the bandwidth and efficiency in antennas is a continuous topic of research in RF systems. However, when it comes to physical platforms that are electrically small relative to the desired frequency of operation, balancing miniaturization, bandwidth, and efficiency is challenging and often counterintuitive. To overcome these challenges, this article proposes utilizing a direct antenna modulated (DAM) electrically small antenna (ESA). Here, we propose using efficiency–bandwidth (EB) product in theoretically analyzing and in measuring the improvement of DAM over a conventional capacitively loaded loop antenna (CLLA). To quantify the benefits of DAM, a prototyped antenna with DAM ($0.0275\lambda \times 0.0251\lambda$) was designed and it successfully transmits a binary-frequency shift keying (BFSK) signal centered at 75 MHz. Though transistor parasitics reduce the possible EB product improvement, $\boldsymbol {\beta }$ , of DAM, measurements show the key importance of maintaining proper switching synchronization to achieve system bandwidths beyond the antenna’s impedance bandwidth. The DAM system achieves significant measured EB product improvement, ${\beta }$ , up to 5 over bit rates of 700 kb/s–7 Mb/s. [ABSTRACT FROM AUTHOR]

Previously, the bandwidth of conventional Doherty power amplifiers (DPAs) is limited by the phase dispersion of the microstrip impedance transformer (IT). To overcome this phase dispersion, minimization of the phase delay of the IT is required, however at the expense of load modulation bandwidth, which limits further bandwidth extension. In this article, we present a broadband Doherty-like PA topology that, for the first time, uses parallel right- and left-handed ITs. This satisfies the minimal phase delay requirement while simultaneously maintaining wideband load modulation. Consequently, the frequency range for load modulation can be significantly extended. For demonstration purposes, a Doherty-like PA prototype is realized using two identical 10-W GaN HEMTs. Measurement results show that a drain efficiency of at least 40% is achieved at 5.2–6-dB back-off from 1.25 to 2.30 GHz, which corresponds to a very wide bandwidth of ~60%. [ABSTRACT FROM AUTHOR]

This article presents the theory and design methodology of broadband RF-input continuous-mode load-modulated balanced power amplifier (CM-LMBA) by introducing the CM output-matching networks in the LMBA architecture. It is illustrated that the CM impedance condition can be achieved by properly adjusting the phase difference between the different PA branches in the proposed CM-LMBA during the entire load modulation process. An RF-input CM-LMBA with 1.45–2.45-GHz bandwidth using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated CM-LMBA attains a measured 11.2–13.4-dB gain and around 40-W saturated power. Power-added efficiency (PAE) of 46.4%–56.5% and 43.2%–50.3% is achieved at 6- and 8-dB output power back-offs throughout the designed band. When driven by a 100-MHz OFDM signal with an 8-dB peak-to-average power ratio (PAPR), the proposed CM-LMBA achieves better than −46-dBc adjacent channel leakage ratio (ACLR) and higher than 45% average PAE after digital predistortion at 1.8 and 2.1 GHz. [ABSTRACT FROM AUTHOR]

In this article, the design method for absorptive balanced rat-race couplers with reconfigurable power-dividing ratio is proposed for the first time. First, the differential-mode (DM) and common-mode (CM) port equivalent impedances of the eight-port balanced network is derived by the even–odd mode method under the mixed-mode isolation and matching conditions. The power-dividing ratio is tuned by changing the admittance ratio of the network components, which greatly extends the amplitude imbalance bandwidth. Then, a nonabsorptive reconfigurable balanced rat-race coupler that consists of transmission lines with adjustable characteristic impedance is proposed. Furthermore, based on the derived DM and CM port equivalent impedances, an absorptive network is designed. Finally, the absorptive reconfigurable balanced rat-race coupler is achieved by attaching the absorptive network at the balanced ports of the designed nonabsorptive reconfigurable balanced rat-race coupler. For verification, the 2-GHz nonabsorptive and absorptive reconfigurable balanced rat-race couplers are designed and measured. The measured results agree well with the simulations. For the nonabsorptive coupler, the measured power-dividing ratio is tuned from −8.5 to 8.9 dB, while the 15-dB DM matching and isolation bandwidth is greater than 370 MHz. For the absorptive coupler, the measured power-dividing ratio is tuned from −8.3 to 9.0 dB, while the 15-dB DM matching and isolation bandwidth and 15-dB CM matching bandwidth are greater than 450 and 1150 MHz, respectively. The measured 0.5-dB amplitude imbalance bandwidths of the nonabsorptive and absorptive couplers are 6%–14.5% and 7%–15.6%, respectively. [ABSTRACT FROM AUTHOR]

A mechanically tunable, constant-absolute-bandwidth (ABW) bandstop filter is realized using the metamaterial-based electromagnetic bandgap structure (MTM-EBG). The MTM-EBG is embedded within a microstrip (MS) line and used to produce a bandstop filtering response, with a topology that is compact, uniplanar, and fully printable. A three-cell MTM-EBG-based MS bandstop filter is designed and experimentally verified for operation centered at 4.18 GHz with a 10-dB rejection bandwidth of 247 MHz. This filter is then made tunable by placing a dielectric plate directly on the surface of the MTM-EBGs. Moving this plate across the surface of the MTM-EBGs changes their reactive loading and, consequently, shifts their response. To ensure a constant ABW, the dielectric plate is perforated to produce an effective plate permittivity that varies for each unit cell. The tunable filter is then fabricated, with the dielectric plate applied to the MTM-EBG-based bandstop filter using a 3-D printed superstructure. A tuning range of 3.80 GHz ± 6.2% and a 10-dB bandstop ABW of 244 MHz ± 1.3% are demonstrated, showing good agreement with the simulated data. The MTM-EBG-based tunable bandstop filter has a variation in ABW comparable to 3-D filters (which typically have substantially lower variation in ABW than fully planar filters) while occupying substantially less area than alternate planar realizations. [ABSTRACT FROM AUTHOR]

This article presents a frequency-reconfigurable outphasing GaAs power amplifier MMIC operating over an 18–38-GHz range with 2–6-GHz RF bandwidth per frequency setting. The architecture is based on a broadband power combining structure providing nonisolating power combining. Reconfigurable shunt elements based on p-i-n diode switches control the Chireix reactance compensation to enable frequency-reconfigurable efficiency enhancement at output power back-off (OBO). The prototype two-stage MMIC is characterized under CW and modulated measurements demonstrating 20–24-dBm saturated output power over the band 18–38 GHz, with measured PAE of 23%–31% at peak and 17%–23% at 6-dB OBO. When measured with a 200-MHz LTE signal with 9-dB PAPR centered at 19.5 GHz, the PA performs with 15.3% average efficiency at a 14.3-dBm average output power with 24.18-dBc ACLR. [ABSTRACT FROM AUTHOR]

This article presents two broadband frequency multiplier chains (FMCs) fabricated with a standard 130-nm SiGe BiCMOS process. In both solutions, a broadband push-push frequency doubler (x2) operating at 220–360 GHz was employed. In order to properly drive such a doubler, with sufficient input power and bandwidth, two different power amplifiers (PAs) have been adopted: the former is based on a cascode configuration and the latter is based on a stacked topology. In addition, a D-band frequency quadrupler (x4) has been integrated before the PAs and doubler, to complete the design of frequency eighth tupler (x8) chains. The first FMC with the cascode PA achieves peak output power of 2.3 dBm, with maximum conversion gain (GC) and bandwidth of 15 dB and 127 GHz, respectively. The second FMC with the stacked PA delivers a saturated output power of 2.5 dBm, with a maximum GC and a bandwidth of 12 dB and 72 GHz, respectively. The two FMCs consume maximum dc power of 0.537 and 0.542 W. The complete design procedure of the FMCs is presented in this article. To the best of our knowledge, the reported bandwidth is state-of-the-art and widest among SiGe based FMCs. [ABSTRACT FROM AUTHOR]

This article presents the principle of coupling fundamental and upper eigenmodes of a ferrite cavity for demonstrating a dual-band stripline circulator. The weak field operation is used for increasing circulation bandwidths and choosing the ratio between the two circulation central frequencies. Indeed, an eigenmode study is presented which identifies parameters that influence the working frequencies and the circulation direction, which can be either the same between the first and the second bands (unidirectional circulator) or different (bidirectional circulator). Two prototypes of dual-band circulators (uni- and bidirectional) have been designed and their measurements validate the developed methodology based on modal analyses. [ABSTRACT FROM AUTHOR]

This article presents a novel architecture of load-modulated balanced amplifier (LMBA) with a unique load-modulation characteristic different from any existing LMBAs and Doherty power amplifiers (DPAs), which is named pseudo-Doherty LMBA (PD-LMBA). Based on a special combination of control amplifier (carrier) and balanced amplifier (peaking) together with proper phase and amplitude controls, an optimal load-modulation behavior can be achieved for PD-LMBA, leading to maximized efficiency over extended power back-off range. More importantly, the efficiency optimization can be achieved with only a static setting of phase offset at a given frequency, which greatly simplifies the complexity for phase control. Furthermore, the cooperations of the carrier and peaking amplifiers in PD-LMBA are fully decoupled, thus lifting the fundamental bandwidth barrier imposed on the Doherty-based active load modulation. Upon theoretical proof of these discoveries, a wideband RF-input PD-LMBA is physically developed using the GaN technology for experimental demonstration. The prototype achieves a highly efficient performance from 1.5 to 2.7 GHz, e.g., 58%–72% of efficiency at 42.5-dBm peak power and 47%–58% at 10-dB output back-off (OBO). When stimulated by a 10-MHz long term evolution (LTE) signal with a 9.5-dB peak-to-average power ratio (PAPR), the developed PD-LMBA achieves an efficiency of 44%–53% over the entire bandwidth at an average output power of around 33 dBm. [ABSTRACT FROM AUTHOR]

The opening of spectral bands in the millimeter-wave (mm-Wave) spectrum from 26 GHz and extending up to the E-band poses new challenges to the power amplifier (PA) design for spectrally agile radios. They are expected to operate with high energy efficiency at peak and back-off levels to process signals with high peak-to-average power ratio (~10 dB), while being able to maintain their performance across a wide range of 5G bands. In addition, the PAs can experience strong load impedance mismatch conditions in a user equipment (UE) that pose additional challenges in handling strong voltage-standing-wave-ratio (VSWR) events. In this article, we present a systematic approach to exploit active load pulling in a multi-port network that synthesizes optimal impedance conditions for 1) broadband peak and back-off operation and 2) mitigating VSWR events at peak power. As proofs of concept, we present two PAs in 65-nm bulk CMOS process. The first chip demonstrates $P_{\text {sat}}$ between 16.3 and 19.3 dBm across 37–73 GHz, with an improvement in the output drain efficiency ($\eta _{\text {out}}$) of up to $3.2\times \!\!/5.8\times $ at 6-/9.6-dB power back-off (PBO) across the frequency range compared to class-A operation. The second chip achieves 26–42-GHz $P_{\text {sat},\, -1 \, {\text{dB}}}$ bandwidth with $P_{\text {sat}} > 19$ dBm and PAE $_{\text {peak}}> 20$ % across all 28–40-GHz bands and with up to $3.35\times $ and $4.84\times $ enhancement in PAE at the PBO levels of 6 and 9.6 dB over class-A operation, respectively. The PA also demonstrates strong tolerance to VSWR events with only 2 dB degradation over a VSWR 4:1 load circle at a frequency of 33 GHz. [ABSTRACT FROM AUTHOR]

High frequency (HF) transmitter implemented with the multioctave broadband power amplifier (PA) enables long-distance communication and has strong survivability. However, it is faced with the problem of harmonics because of the nonlinearity of the PA. We first consider canceling the harmonics using a harmonic cancellation digital predistortion (HC-DPD) technique, instead of lossy and bulky analog filter banks. A uniform complex-valued Hilbert transform-based polynomial (HTBP) function is proposed for the modeling of the harmonics, as well as the fundamental component in the real-valued input and output signals. In order to validate this idea, detailed experiments were performed for carrier frequencies located at 5 and 10 MHz, respectively. After the proposed HC-DPD, the harmonics were all canceled to satisfy the linearization requirements. In particular, the improvement of the second harmonic is more than 40 dB, which is nearly 20 dB better than that of the memoryless polynomial (MLP) model. Furthermore, the experimental results demonstrate that the proposed technique is scalable, in which the model coefficients extracted at a specific power level, signal bandwidth, and carrier frequency can be extended to other scenarios. Both the second and third harmonics were canceled for being below −45 dBc after the HC-DPD. [ABSTRACT FROM AUTHOR]

Achieving a fractional bandwidth (FBW) of more than 60% has been a challenging problem for two-way symmetrical Doherty power amplifiers (TW-SDPAs) that are designed using a continuous-mode technique. As reported in the literature, these designed continuous-mode-based TW-SDPAs possess less than 52% FBW, which cannot satisfactorily meet the challenging, complex, and ever-evolving modulation schemes’ demands. To overcome such a limitation, this article proposes a novel approach based on fuzzy logic techniques able to simplify and speed up the design of continuous-mode-based TW-SDPAs with the state-of-the-art FBW. In particular, the proposed technique uses the $K$ -means unsupervised learning clustering algorithm and the continuous-mode technique in a modeled fuzzy logic system environment. As a result, extensive impedance solution design space is readily made available and the optimal impedances required by the carrier and peaking subamplifiers for efficiently operating at the saturation and output-power-back-off (OPBO) levels are automatically obtained. For verification, a TW-SDPA was designed and measured. According to the measured results, the TW-SDPA operates within the 1.2–2.4-GHz frequency band corresponding to 66.7% FBW. As compared with the designed continuous-mode-based TW-SDPAs reported in the literature, this article indicates over 15% increment in FBW. Moreover, 41.59%–81.1% drain efficiency (DE) at saturation, 35%–63% DE at 6-dB OPBO, 42–45-dBm output power, and 7–10.52-dB gain were successfully achieved. Adjacent channel leakage ratio (ACLR) better than −46 dBc and average DE within 46%–55% were successfully recorded after linearization. [ABSTRACT FROM AUTHOR]

The analysis and design of an RF-input sequential load modulated balanced power amplifier (SLMBA) are presented in this article. Unlike the existing LMBAs, in this new configuration, an over-driven class-B amplifier is used as the carrier amplifier while the balanced PA pair is biased in class-C mode to serve as the peaking amplifier. It is illustrated that the sequential operation greatly extends the high-efficiency power range and enables the proposed SLMBA to achieve high back-off efficiency across a wide bandwidth. An RF-input SLMBA at 3.05–3.55-GHz band using commercial GaN transistors is designed and implemented to validate the proposed architecture. The fabricated SLMBA attains a measured 9.5–10.3-dB gain and 42.3–43.7-dBm saturated power. Drain efficiency of 50.9–64.9/46.8–60.7/43.2–51.4% is achieved at 6-/8-/10-dB output power back-off within the designed bandwidth. By changing the bias condition of the carrier device, higher than 49.1% drain efficiency can be obtained within the 12.8-dB output power range at 3.3 GHz. When driven by a 40-MHz orthogonal frequency-division multiplexing (OFDM) signal with 8-dB peak-to-average power ratio (PAPR), the proposed SLMBA achieves adjacent channel leakage ratio (ACLR) better than −25 dBc with an average efficiency of 63.2% without digital predistortion (DPD). When excited by a ten-carrier 200-MHz OFDM signal with 10-dB PAPR, the average efficiency can reach 48.2% and −43.9-dBc ACLR can be obtained after DPD. [ABSTRACT FROM AUTHOR]

We have demonstrated a frequency multiplier-based multiplying transmitter (MT) architecture, which shows the transmission of wideband modulated signals from the lower frequency band to the millimeter-wave (mm-wave) through the frequency multiplier directly is a viable option. To compensate for the severe nonlinear distortions exhibited by the frequency multiplier in a more efficient way, a two-stage cascaded digital predistortion (DPD) scheme with constrained feedback bandwidth is proposed. The complexity-reduced generalized memory polynomial (GMP) and $N$ th-order power/root module are used for nonlinear behavioral modeling. Furthermore, the spectral extrapolation and band-divided (BD) modeling methods are employed to achieve more accurate linearization performance of the frequency multiplier over the limited feedback bandwidth. The MT experimental system with an active frequency quadrupler at the Q-band was set up to evaluate the linearization capacity of the proposed BD $N$ th-order cascaded complexity-reduced GMP (BD-N-CGMP) DPD scheme. In the test for 24-MHz bandwidth 16 quadrature amplitude modulation (QAM) signal, the frequency quadrupler’s linearized output at 48.6 GHz with error vector magnitude (EVM) of 1.94% and adjacent channel power ratio (ACPR) of −47.2 dBc could be achieved, even when the feedback bandwidth was limited from 480 to 78 MHz. This demonstrated system significantly decreased the requirement of the digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) sampling rate, and showed promising performances for future MT architecture at mm-wave and sub-terahertz (sub-THz) frequencies with large signal bandwidth. [ABSTRACT FROM AUTHOR]

Mushroom-type electromagnetic bandgap (EBG) structures are known to operate as high-impedance surfaces at low-frequency bands. They are broadly used in the microwave regime. However, one of the main drawbacks of mushroom-type EBG structures is their narrow bandwidth. In this article, we propose a mushroom-type EBG structure with glide-symmetric edge vias to increase the operational bandwidth. This bandwidth increment is explained by the physical insight provided by an equivalent circuit model of the structure as well as the description of the field behavior. Simulation and measurement results show an improvement of approximately 67% over the case without glide symmetry in the structure. We conclude that applying glide symmetry to the mushroom-type EBG structures can improve their bandwidth without adding additional manufacturing costs. [ABSTRACT FROM AUTHOR]

In this article, for the first time, a novel four-port coupler with reconfigurable multifunctions of filtering rat-race coupler (FRC), filtering branch-line coupler (FBC), and conventional single-ended two-port multipole bandpass filter (BPF) is proposed. It simply consists of four varactor-loaded stepped-impedance resonators that are arranged symmetrically. Through appropriate coupling-type (electrical coupling or magnetic coupling) conversion, 90° or −90° phase shift between the adjacent resonators can easily be obtained and works as a key factor in the transformation between different filtering coupler modes. With this simple configuration, the proposed coupler achieves reconfigurable FRC and FBC with not only operating frequency tuning over a wide tuning range but also bandwidth and power division ratios (PDRs) control for each filtering mode. In addition, by imposing open circuit at any two ports, the four-port coupler can be converted to the conventional single-ended two-port BPFs with reconfigurable filter orders of second, third, and fourth. The measured results show that the FRC and FBC can continuously cover the frequency ranges of 1.21–1.67 and 1.2–1.61 GHz with −1-dB bandwidth tuning of 60–120 and 55–110 MHz, respectively. The 3- and 6-dB PDRs have been demonstrated for both filtering coupler modes. In single-ended two-port BPF mode, the frequency tuning ranges are measured of 1.12–1.6, 1.16–1.6, and 1.2–1.61 GHz, respectively, for the proposed two-port second-, third-, and fourth-order BPFs. Measured and simulated results are in good agreement, validating the proposed design method. [ABSTRACT FROM AUTHOR]

In this article, we present a novel technique to build digital predistorters that can linearize broadband power amplifiers (PAs) using reduced sampling rates. In contrast to conventional digital predistortion (DPD) where oversampling is necessary to avoid aliasing effect, the proposed method cancels the aliasing distortion using a sliced multistage cancellation scheme. A large reduction of sampling rate can be achieved in digital implementation of DPD, significantly reducing power consumption and implementation cost. Experimental results show that a DPD with a sampling rate of merely $1.5\times $ , instead of $5 \times $ , signal bandwidth, can still produce satisfactory performance within the linearization bandwidth but consume only one-third of power, compared with that using the conventional approaches. The proposed technique provides a promising solution for the next-generation 5G systems, where large signal bandwidths are required. [ABSTRACT FROM AUTHOR]

Radar-absorbing structures (RASs) with improved mechanical properties and subwavelength thickness are of particular interest for aerospace applications and electromagnetic (EM) interference control. This article proposes a new RAS, made of a graphene-filled lossy laminate (LL) with impedance adapter, having a total thickness less than 4 mm and a normalized absorption bandwidth of 84% in the frequency range 6–18 GHz. The RAS is designed by applying an innovative simulation approach of the graphene-filled LL, which is based on the multiscale Maxwell Garnett model and the effective medium theory. Experimental tests are performed in order to validate the developed model and to assess the absorption properties of the produced RAS, having a minimum reflection of −30 dB and an absorption bandwidth at −10 dB of 10 GHz, with a central frequency of 12 GHz and a graphene nanoplatelets concentration less than 5 g/m2. [ABSTRACT FROM AUTHOR]

This article proposes a new approach for designing high-power Doherty power amplifiers (DPAs) with extended bandwidth. The analysis starts with a generic series-connected load (SCL) DPA architecture to derive equations that relate the $ABCD$ parameters of the output combiner to the transistors’ optimum and load impedances. These equations make it possible to significantly increase the load impedance in the SCL DPA compared to the more popular parallel-connected load (PCL) DPA architecture—a feature of particular importance when targeting very high output power DPAs for macrocell base stations and broadcast applications. High-power PCL DPAs require very low load impedance, seriously complicating their design and limiting the achievable bandwidth of the DPA. To further maximize the load impedance increase, the proposed SCL DPA uses a push–pull topology for the main and peaking amplifier stages. A low-loss planar balanced-to-unbalanced transformer (balun)-based combiner network is then utilized to realize the DPA series-connected combiner while absorbing the transistor’s parasitics. The proposed approach is applied to design a proof-of-concept 350-W SCL DPA operating over the band spanning from 720 to 980 MHz. The prototype demonstrated a peak output power of about 55 dBm over a 30% fractional bandwidth with a 6-dB back-off efficiency, measured using a pulsed signal, of between 46.6% and 54.6%. Furthermore, the modulated signal-based measurement results confirmed the linearizability of the SCL DPA prototype, while it maintained a back-off efficiency over 50% for a signal with 7.1-dB peak-to-average power ratio. [ABSTRACT FROM AUTHOR]

Frequency-adaptive bandpass diplexer (FA-BPD) with constant absolute bandwidths (ABWs) and two identical passbands at every state is the most useful duplexing tunable filter for the smart frequency-division duplex (FDD) system. However, it is widely considered a challenge. In this article, we propose a new synchronously tuned trimode resonator (STTR) to achieve such a type of FA-BPDs. The proposed STTR has three flexible resonant modes that are able to be synchronously tuned by only one bias with the predefined frequency spacings. The spacings between every two tunable resonant frequencies can be precisely controlled as desired. Consequently, the resultant tunable filters can be implemented with different constant ABWs and at the different center frequency, which makes it possible to achieve two frequency-adaptive bandpass filters (FA-BPFs) at different frequency ranges but with the same ABW. Based on the proposed STTR, a three-pole FA-BPF with nearly 250-MHz ABW is examined. Using the FA-BPF as basic building blocks, a 1.5–3.5-GHz FA-BPD with identical passband and constant ABW is developed finally. The simulation and measurement results confirm the proposed design method and also exhibit the merits, such as low loss, simple design, wide frequency tuning range with synchronous passband. [ABSTRACT FROM AUTHOR]

We propose a supercompact and ultrawideband (UWB) bandpass filter for spoof surface plasmonic polariton (SSPP) mode. By using meander-line technology, the electrical size of the proposed SSPP structure is reduced dramatically, which is only about 1/4 of the traditional rectangular-groove structure with the same geometry. Based on the proposed SSPP structure, we construct a supercompact UWB bandpass filter working in the frequency range of 0.25–4.5 GHz, whose geometric size is only $87.5\times12.8$ mm2. The upper cutoff frequency of the passband can be controlled by changing the meander-line design of the SSPP unit, and the lower cutoff frequency of the passband is determined by the capacitive coupling of the feeding structure. Both the simulation and experimental results show that the UWB SSPP bandpass filter is centered at 2.4 GHz with an extremely wide relative bandwidth of 174%, whose electrical size is only $0.7\lambda \,\,\times 0.1\lambda $ at the central frequency. [ABSTRACT FROM AUTHOR]

An investigation of the single-frequency iteration method for synthesizing mode converter is taken, and the results show that the synthesized structure has an almost constant perturbation period, which limits the bandwidth of the mode converter. Therefore, a multifrequency iteration method based on variable perturbation periods is proposed to design a broadband oversized TE01-to-TE11 mode converter in this article. To avoid the interference among the perturbation periods corresponding to different frequencies, a weight function is introduced to separate these periods from each other. Using the proposed method, a TE01-to-TE11 mode converter is designed with the conversion efficiency over 95% in the range of 32.5–36.2 GHz (the relative bandwidth of 10.77%). To validate the performance of the proposed mode converter, a prototype is manufactured and measured. In the S-parameters measurement, an average conversion efficiency exceeding 93% and an average ohmic loss near 3% are obtained in the range of 32.3–36.2 GHz. The high purity of circular TE11 mode is demonstrated at the output of the fabricated mode converter according to the measured field patterns. [ABSTRACT FROM AUTHOR]