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This paper presents the design of a broadband and high-power amplifier with bounded performance technique (BPT). Like the real frequency technique (RFT) or the simplified RFT (SRFT), BPT achieves broadband performance via matching at some in-band discrete real frequencies. It solves some design issues that are not addressed in the RFT and the SRFT. Among them are the inclusion of the design specifications in the device selection and design process and the possible degradation of operation metrics that are not optimized. BPT also avoids complicated analytic mathematics by using circuit prototypes. In this paper, we show the design of an amplifier with BPT. It has a 3-dB compression power of at least 100 W and a drain efficiency of at least 50% over the band 1–2.8 GHz or 94.7% fractional bandwidth. We also show the design of the same amplifier with the traditional SRFT and compare its expected performance with that designed with BPT. [ABSTRACT FROM AUTHOR]

This paper addresses the estimation and compensation of I/Q imbalance, one of the most prominent impairments found in wideband zero-intermediate frequency transceivers (TRxs). The I/Q imbalance encountered in this kind of TRx comprises not only frequency-selective gain and phase imbalance but also delay imbalance. Unless appropriate compensation is applied, the I/Q imbalance significantly degrades the performance of a communication system. This paper presents a novel compensation technique for transmitter I/Q imbalance based on built-in-self-calibration, a low cost and robust compensation technique that enables manufacturing as well as in-field calibration with low computational complexity. The method's performance is evaluated in a TRx with 64-quadratic-amplitude modulation and 2 GHz of bandwidth implemented with real hardware. The measurements show that the proposed technique achieves an image rejection ratio greater than 35 dB in the entire 2 GHz bandwidth and an error vector magnitude lower than 3%. [ABSTRACT FROM AUTHOR]

Time-reversal (TR) methods have been applied to reconstruct electromagnetic sources. Electromagnetic signals emitted by unknown sources are received at preselected output locations in a loss-free ergodic cavity, reversed in time, and then reinjected back into the output locations; the peak values of the resulting fields in the cavity indicate in most cases the original source locations. In this paper, we summarize the theoretical foundations of computational TR in terms of the finite-difference time-domain model and derive a condition for reconstructing multiple sources without the need to know the Green’s functions and to identify the field peaks. We then develop a method to apply this new approach to practical problems. Furthermore, we develop a method to reconstruct sources effectively from band-limited field responses. Thus, practical applications of the TR method become feasible. Numerical experiments are provided to verify the theoretical analyses and effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

This paper presents a broadband efficient power amplifier (PA) targeting sub-6-GHz 5G base station applications. Due to the demanding requirements in both peak-to-average power ratio (PAPR) and bandwidth in 5G systems, we employ a combination of both load and supply modulation for efficiency enhancement. Active matching, implemented using an RF-input load-modulated balanced amplifier (LMBA) architecture, enables efficient octave-bandwidth operation. Supply modulation, which is carrier frequency agnostic, is then used to further extend the back-off efficiency. This paper focuses on a study of supply modulation strategies for the load-modulated PA using an efficient GaN eight-level discrete supply modulator. To overcome the bandwidth limitations associated with discrete-level switching, a commutation rate reduction (CRR) filter is applied in digital baseband and its effects are analyzed theoretically and experimentally. The supply-modulated LMBA is characterized across 1.8–3.8 GHz with 100-MHz, 10-dB PAPR signals. An output power of 34 dBm with average composite (total) PAE ranging from 22.4% to 43.9% across the band is demonstrated, with an ACLR of about −50 dBc after digital predistortion. [ABSTRACT FROM AUTHOR]

This paper proposes a measurement strategy to remove the random phase contributions of the sweeping local oscillator (LO) from modulated radio frequency phase measurements based on downconversion. To obtain a stable phase spectrum for each run of tone-by-tone sweeping measurement, the LO used for downconversion is coupled out to an extra path and modulated to be a wideband multisine signal. By monitoring the phase change of multisine signal at a specific and fixed frequency point, random LO phase offsets during the frequency sweep can be measured and compensated. In this paper, two experimental test benches with the same core measurement strategy but different architectures are established for method validation. According to the experimental results using test bench one, the phase stability is ±(0.2°–0.4°) at 1.8 GHz for fundamental mixing-based downconversion and ±(0.6°–1°) for harmonic mixing at 6 GHz. Based on test bench two, relative phase deviations of ±(0.8°–1.2°) at 22 GHz for fundamental mixing and ±(2°–3°) at 66 GHz for harmonic mixing are reachable. [ABSTRACT FROM AUTHOR]

A noise match network for the LC-ladder input network of a broadband inductively source-degenerated common-source (CS) field effect transistor (FET) low-noise amplifier (LNA) is established through noise transformation matrix to derive the noise parameters of a broadband LNA. Analytical formulas for the noise factors of a CS FET LNA with a three-section LC-ladder input network are thus obtained based on the design algorithm of optimal noise and input match developed in this paper. Two 3.7–10.5 GHz two-stage LNAs of the same topology are demonstrated using 0.15- \mu \textm pHEMT technology to validate the design methodology. One LNA has all the fully integrated inductors and the other uses two on-chip inductors replaced by two high-Q bondwire inductors for better noise performance. The measurement results show 11-dB power gain with 2.1-dB noise figure for the LNA with the fully integrated inductors and 11-dB power gain with 1.6-dB noise figure for the LNA with two bondwire inductors, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents a balanced frequency doubler with 6.5-dBm peak output power at 204 GHz in 130-nm SiGe BiCMOS technology ( fT/f\max =210 /250 GHz). To convert the single-ended input signal to a differential signal for balanced operation, an on-chip transformer-based balun is employed. Detailed design procedure and compensation techniques to lower the imbalance at the output ports, based on mixed mode S parameters are proposed and verified analytically and through electromagnetic simulations. The use of optimized harmonic reflectors at the input port results in a 2-dBm increase in output power without sacrificing the bandwidth of interest. The measured conversion loss of the frequency doubler is 9 dB with 6-dBm input power at 204-GHz output. The measured peak output power is 6.5 dBm with an on-chip power amplifier stage. The 3-dB output power bandwidth is measured to be wider than 50 GHz (170–220 GHz). The total chip area of the doubler is 0.09 mm2 and the dc power consumption is 90 mW from a 1.8-V supply, which corresponds to a 5% collector efficiency. [ABSTRACT FROM PUBLISHER]

In this paper, a two-stage broadband CMOS stacked FET RF power amplifier (PA) with a reconfigurable interstage matching network is developed for wideband envelope tracking (ET). The proposed RF PA is designed based on Class-J mode of operation, where the output matching is realized with a two-section low-pass matching network. To overcome the bandwidth (BW) limitation from the high- Q interstage impedance, a reconfigurable matching network is proposed, allowing a triple frequency mode of operation using two RF switches. The proposed RF PA is fabricated in a 0.32-\mu\m silicon-on-insulator CMOS process and shows continuous wave (CW) power-added efficiencies (PAEs) higher than 60% from 0.65 to 1.03 GHz with a peak PAE of 69.2% at 0.85 GHz. The complete ET PA system performance is demonstrated using the envelope amplifier fabricated on the same process. When measured using a 20-MHz BW long-term evolution signal, the overall system PAE of the ET PA is higher than 40% from 0.65 to 0.97 GHz while evolved universal terrestrial radio access adjacent channel leakage ratios are better than -\33 dBc across the entire BW after memoryless digital pre-distortion. To our knowledge, this study represents the highest overall system performance in terms of PAE and BW among the published broadband ET PAs, including GaAs HBT and SiGe BiCMOS. [ABSTRACT FROM AUTHOR]

In this paper, a novel terminated coupled line structure (TCLS) is introduced, which is constructed by a coupled line section and four terminations loaded on it. Introducing different kinds of terminations, three types of bandpass filters (BPFs) based on TCLSs are proposed, theoretically analyzed, and fabricated, including two single-ended wideband BPFs with fractional bandwidths (FBWs) of 67% and 40% respectively, and a wideband differential BPF with 74% differential-mode FBW. These BPFs can achieve wide passband bandwidth, low in-band insertion loss, high passband selectivity, as well as deep stopband rejection performance simultaneously, benefited from the multiple transmission zeros and transmission poles obtained by the TCLSs. The practical design procedures of these BPFs are presented and explained. The agreement among theoretical predictions, EM-simulated, and measured results validates our proposed filter structures. Finally, the generalized multistage filter topology based on TCLSs is proposed to design high-order filters with better filtering performances. [ABSTRACT FROM PUBLISHER]

In this paper, a novel broadband Doherty power amplifier based on the continuous-mode technique (C-DPA) is proposed. The amplifier is focused on manipulating harmonic components in a Doherty power amplifier (DPA) structure to achieve improved bandwidth and efficiency. In a conventional DPA, harmonic isolation is typically required between the two transistors to prevent them from modulating each other at harmonic frequencies. However, as presented in this paper, such isolation is not actually necessary. On the contrary, by allowing the two transistors to modulate each other at harmonic frequencies with the help of a properly designed postharmonic tuning network, a series of highly efficient DPA modes can be created over a continuous frequency band, leading to a broadband C-DPA. Based on the proposed method, an example of a C-DPA working from 1.65 to 2.75 GHz was designed. According to the measured results, the designed C-DPA exhibits a 52%–66% efficiency at a −6 dB power backoff and a power utilization factor higher than 1.08 over the 1.1-GHz band. In addition, when simulated by a 7.5-dB peak-to-average power ratio 20-MHz LTE signal, the example C-DPA exhibits an efficiency of 46%–62% while maintaining an adjacent channel power ratio below −45 dBc after linearization over the full 1.1-GHz band. To the best of our knowledge, this is the first proposed C-DPA and a state-of-the-art performance for broadband DPAs. [ABSTRACT FROM PUBLISHER]

In-band full-duplex (IBFD) wireless systems offer the ability to revolutionize frequency spectrum utilization for future networks. This is only possible if the self-interference generated by each wireless node is sufficiently mitigated, and becomes more challenging as the bandwidth increases. RF cancellation is one of the critical components that enables this interference reduction, but has previously been limited to narrowband operation or restricted to distinctive environments. This paper presents a novel RF canceller that utilizes photonic components to create a wideband vector modulator architecture with tunable time-delay taps. A prototype system with 20 canceller taps has been demonstrated to provide 25 and 20 dB of cancellation over 500-MHz and 1-GHz instantaneous bandwidths, respectively, and is tunable between 0.5 and 5.5 GHz. This unique photonic-enabled RF canceller design provides a path forward to achieve the wideband operation and high tap counts that will be required to successfully deploy future wireless systems with IBFD technology. [ABSTRACT FROM AUTHOR]

This paper describes the novel design concept of a wideband noncircular choke flange for connecting two contactless waveguide joints with the variable air gap. Resonant enhancement of transmission loss is observed in the experiment as well as the numerical simulation in Ansys HFSS software when a 2-D standing wave is excited in the narrow air gap. The shape of the choke groove is designed in such a way that ensures standing waves cannot be excited in the frequency band of interest, even considering possible linear and rotational misalignments between the connecting joints during practical operation, thereby making the design very robust. The eigenmode analysis is performed to decompose the mixed excitation mode into the fundamental and higher order modes, and for the case of misalignment, revealing why the electric field changes the direction of rotation above and below the resonant frequency. Experimental measurement results of the fabricated egg-choke flange showed that the transmission loss is less than 0.1 dB in the 2.5-GHz bandwidth from 8.5 to 11 GHz with possible misalignment which validates the design. Other choke shapes are possible following the same design methodology with different scaling parameters depending on the desired frequency band of the user application. [ABSTRACT FROM AUTHOR]

Four novel architectures of wideband five-port single-ended-to-balanced power dividers with broadband common-mode suppression are proposed in this paper. The bandpass filtering capability with/without close-to-passband transmission zeros are also incorporated in some of them to obtain multifunctional single-ended-to-differential-mode filtering/power division operation. Two ideal 180° phase inverters are used to replace the conventional half-wavelength transmission line-based inverters in the basic power divider structure so that wideband common-mode rejection and a smaller circuit size are achieved. Quarter-wavelength transmission lines and coupled-line sections are exploited to simultaneously realize the bandpass filtering and wideband power division functionalities. Each five-port power divider exhibits broadband 3-dB single-ended-to-balanced power division, high in-band input–output power-matching levels, high in-band power isolation levels between the two balanced outputs and wideband common-mode rejection. The theoretical analysis, parametric study, and design procedure for the conceived single-ended-to-differential-mode power dividers are provided. Furthermore, for experimental and demonstration purposes, four microstrip prototypes designed at 1 GHz are manufactured and characterized. [ABSTRACT FROM AUTHOR]

In this paper, we present a frequency analysis of a compensated impedance inverter and its effective implementation in the context of high-power Doherty amplifier (DPA) design. On the basis of an idealized DPA model, we calculate the expected operative bandwidth and the corresponding maximum drain efficiency as a function of the modulated signal statistics. In addition, we introduce an effective technique for the implementation of the compensated impedance inverter, suitable for preserving its broadband characteristics in the presence of large device’s output capacitance. The implementation technique is based on the generalized equivalent transmission-line equivalence principle, which considers both shortening and lengthening the equivalent transmission lines. We demonstrate that, by the proposed approach, parasitic absorption is possible maintaining a low $Q$ -factor of the equivalent network. The technique is validated by the development of a silicon laterally diffused metal–oxide–semiconductor DPA with optimized peak power and efficiency for applications in the 650–950-MHz band. The fabricated prototype is characterized by an LTE signal with a 20-MHz bandwidth and peak-to-average-power ratio of 7.5 dB and features an average drain efficiency between 37% and 47%, with an average power of 49 dBm across 37.5% of the bandwidth. [ABSTRACT FROM PUBLISHER]

The development of the communication networks tends gradually toward exploiting higher frequencies, sometimes even reaching the lowest microwave band (P-band). As the signal bandwidth used for transmission over twisted-pairs increases, as recommended by G.fast and other broadband systems, new phenomenon was observed, namely, backscattering. Motivated by the measurements of copper cables in frequency band up to 400 MHz, we propose a novel backscattering model. It may be productively applied to the problem of loop diagnostics. The methods to accurately and reliable determine the relevant transmission-line parameters are sine qua non condition to appropriately exploit the potential of short-to-medium range access lines. In this paper, a recursive formulation of the frequency-domain response of the backscattering is used for a space–time characterization. To confirm the practical use of the finding, we evaluate the properties of a loop using wideband, high-frequency $S_{11}$ measurements of the real cables. These laboratory results confirm the effectiveness and accuracy of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a monolithic microwave integrated circuit multifunction chip implemented using a 0.25- \mu \textm gallium arsenide pseudomorphic high-electron-mobility transistor process for use in a phased array jammer transmitter. This chip, which operates in the frequency range of 6–18 GHz, provides several functions including 8-bit true time delay (TTD), 7-bit attenuation, wideband amplification, and digital serial-to-parallel conversion for 15-bit control. The TTD and attenuation coverage are 255 ps with a step of 1 ps and 31.75 dB with a step of 0.25 dB, respectively. The TTD employing an artificial transmission line configuration demonstrates a root-mean-square delay error of less than 1.7 ps in the operating frequency range. The chip has a compact size of 4\,\,\ mm \times 5 mm and exhibits a typical gain of 12 dB and an output P1dB of 16.5 dBm over a frequency range of 6–18 GHz. [ABSTRACT FROM PUBLISHER]

A broadband and highly efficient class-G supply modulated power amplifier (PA) system with 120-MHz instantaneous modulation bandwidth operating in the 1.8-GHz band is presented in this paper. The core element is the fast class-G supply modulator which switches the supply voltage of the RF PA between three discrete levels with a minimum pulse duration of 2.5 ns. Two designs for the drain bias interface between PA and modulator are evaluated where the best results are achieved for an implementation based on a $\lambda $ /4-wavelength RF-choke. Measurement results are presented for a 120-MHz contiguous carrier aggregated signal using eleven subcarriers with modulation bandwidths ranging from 5 to 20 MHz for each subcarrier. In combination with digital predistortion, the system achieves 38.5% PAE with −40-dB EVM and −46-dB ACLR for the 120-MHz multicarrier signal with a peak-to-average power ratio of 10 dB at the PA output and 39-dBm average output power. The total efficiency enhancement achieved by the class-G modulation is 13% points. [ABSTRACT FROM PUBLISHER]

The nondestructive characterization of biological liquids and cell suspensions using electromagnetic waves in the microwave frequency range calls for accurate and sensitive measurement devices. Especially when reducing the sample volume, the sensitivity becomes a critical design parameter for broadband sensors. In this paper, a miniaturized transmission-line sensor based on a coplanar waveguide is used to characterize the permittivity of nanoliter volumes of biologically relevant liquids and cell suspensions. The sensor’s sensitivity is increased by means of electrically small discontinuities within the sensing section. The biological samples are guided across the sensor in a microfluidic channel, which is fabricated using microsystems technology. The sensor is used between 850 MHz and 40 GHz to detect the broadband permittivity of liquid samples such as aqueous salt and protein solutions. The experimentally detected contrast between living and dead Chinese hamster ovary cells in suspension is significant despite the small sample volume. [ABSTRACT FROM PUBLISHER]

This paper presents a stacked RF front-end (RFE) package for wideband receiver applications. While having a power consumption of 18 mW, the flipped CMOS chip consisting of a low-noise amplifier and a quadrature down-conversion mixer stacks on a glass integrated passive device (GIPD) substrate, subsequently achieving a noise figure of 2.2–2.8 dB and a conversion gain of 23–25 dB over 1–6 GHz. Moreover, the RFE package uses a GIPD balun with a high common-mode rejection ratio and a post-distortion linearizer in the CMOS mixer, subsequently resulting in an IIP2 of 57–68 dBm and an IIP3 of -5.2–-3.5 dBm over the entire operating band. This paper also elucidates how coupling between the flipped CMOS chip and GIPD balun affects the RFE linearity. Fabricated with 0.18-\mu\ m CMOS technology, the flipped CMOS chip is packaged on the GIPD substrate with a footprint area of \1.8\times \1.8\ \ mm^2. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel dual-mode substrate integrated waveguide (SIW) filter technique. Based on the conventional dual-mode SIW structure, further investigation is performed. Multiple transmission zeros can be obtained at one side or both sides of the passband for an SIW cavity. Therefore, flexible design and high performance response can be available for dual-mode SIW filter. A dual-mode SIW bandpass filter with quasi-elliptic response and a dual-mode SIW diplexer with asymmetric channel response are simulated, fabricated, and measured to demonstrate and verify the novel property. [ABSTRACT FROM PUBLISHER]

In this paper, an augmented dual-band digital predistortion (DPD) technique for reducing the cross-band intermodulation distortion (IMD) using predictive injection technique is proposed to address some of the shortcomings of dual-band DPDs. The technique alleviates the need to observe the cross-band third-order IMD (IMD3) terms in the feedback loop by predicting the distortion terms and generating synthetic signals, which are then injected at the transmitter side. To highlight the issue, the wideband and dual-band DPD architectures and their respective limitations are briefly outlined. The theory behind the proposed concept is developed, and practical measurements performed using a Class AB power amplifier driven by a long-term evolution signal are provided to support the theory. The results obtained show that the proposed method achieves promising performance in mitigating the cross-band IMD3 issue faced by dual-band DPDs. This technique can be extended to mitigate higher order cross-band distortion as well. [ABSTRACT FROM PUBLISHER]

The mode converter is a key component in a gyrotron traveling-wave tube (gyro-TWT) application system, which can transform the output circular TE $_{0n}$ modes (in a gyro-TWT loaded with lossy ceramic dielectric or photonic bandgap interaction structure, the output mode is normally a TE $_{0n}$ mode) into a mode conducive to transmission and emission (linearly polarized Gaussian-like HE11 mode). In particular, the bandwidth of the TE01–TE11 mode converter is the most important challenge in the conversion sequence. In this paper, based on the deformation of the transverse cross section and the modified multi-frequency iteration synthesis technique along the longitudinal propagation axis, a novel method for synthesis of a broad bandwidth mode converter is proposed. Then, an application of the method to a wideband serpentine TE01–TE11 mode converter with an elliptical section is given. This novel mode converter including transitional waveguides achieves a 19.18% relative bandwidth (conversion efficiency over 95%) at center frequency 30.5 GHz, which increases nearly 195% compared with the conventional circular design, and its structure length is 1151.65 mm. Overall, this method offers a novel solution to the requirement of broad bandwidth in the high-power microwave transmission system. [ABSTRACT FROM AUTHOR]

In this paper, the design of a cavity crossover with three intersecting channels is presented. The three fundamental modes of a cavity resonator, namely, TE011, TE101, and TM110 modes, are adopted to resonate at each of three channels, respectively. Due to the modal orthogonality of these fundamental modes, high isolation among three channels can be achieved. Two kinds of crossovers, for narrowband and broadband applications, are presented. For the narrowband case, the proposed crossover resonates at 2.91 GHz with the fractional bandwidth of 1.4%. For the broadband case, the proposed crossover resonates at 3 GHz with the fractional bandwidth of 24%. The isolations of both designs reach more than 50 dB. For a proof of concept, the broadband example of the cavity crossover structures is fabricated and measured. A good agreement between the simulated and the measured results verifies the accuracy of the proposed design methodology. [ABSTRACT FROM AUTHOR]

This paper presents a broadband three-stage Doherty power amplifier (DPA) using impedance compensation for bandwidth extension. Different from the conventional design, an impedance-compensating load combiner is proposed to broaden the bandwidth of the three-stage DPA by employing the output impedances of the peaking amplifiers. Considering the load impedance of the peaking branch as an independent design variable, the Doherty load modulations are analyzed in theory, pointing out the optimized solution for the load combiner. To achieve the impedance compensation, the peaking output matching networks are deliberately designed with the dual-impedance matching topology. Experimental results show that a three-stage DPA is realized from 1.6 to 2.6 GHz (48% fractional bandwidth) with a measured efficiency of 50%–53% at 9.5-dB back-off and a saturated output power around 45.5 dBm. When stimulated by the 20- and 40-MHz modulated signals at an average output power of around 36.5 dBm, the proposed DPA can achieve the adjacent channel leakage ratio of −50 dBc over the whole frequency band after linearization, with an average efficiency of higher than 50%. [ABSTRACT FROM AUTHOR]

We present a stripline design and calibration method allowing the extraction of relative permittivity of single dielectric samples in the 200-MHz–50-GHz range. The simultaneous extraction of relative permittivity and permeability is also illustrated by characterizing a set of samples comprising magnetic inclusions over the same frequency range. The calibration method involves the use of seven measurements of the stripline scattering parameters (S-parameters) with different length shorts inserted. From these measurements, it is possible to determine the reflections at the transition regions of the stripline to correct the measured S-parameters for characterization. By quantifying a range of samples with increasing percentage volume filling of barium titanate in polyurethane for the case of dielectric samples, and carbonyl iron powder for magnetic samples, this paper demonstrates a reliable method for the broadband characterization of composite materials. [ABSTRACT FROM AUTHOR]

This paper analyzes and accurately models the complex noise behavior of vector network analyzers (VNAs) when measuring large-mismatch devices and subsequently shows how the VNA measurement noise performance is enhanced through implementation of a high-speed, broadband, active RF interferometer module. The presented VNA noise model provides a solid framework, benchmarked by measurement data, to analyze existing RF interferometer approaches. The performance improvement of the proposed interferometer implementation is then benchmarked in terms of magnitude and phase stability of the renormalized impedance level. A test bench employing the novel add-on RF interferometer module is presented and demonstrated to achieve high-speed cancellation of the scattered wave over a broad frequency band. The first experiment shows ultralow noise in a 1–18 GHz broadband measurement of co-planar waveguide 0.5- $\Omega $ and 5- $\text{k}\Omega $ impedance standards. Employing the proposed hardware setup improves the noise uncertainty for the 5- $\text{k}\Omega $ impedance standard by a factor of 8 and 20 at 1 and 18 GHz, respectively. In the second experiment, a factor of 2 height-resolution enhancement is achieved in a scanning microwave microscope when the RF interferometer module is added to the instrument. [ABSTRACT FROM AUTHOR]

This paper proposes a novel configuration for a phased-array antenna system (PAS) that achieves ultrabroadband transmission using millimeter-wave (mm-wave) and quasi-mm-wave. Since a PAS is expected to employ an unprecedented number of antenna elements to compensate for propagation loss in high-frequency bands, the configuration must be compact and cost effective. A PAS that employs radio frequency (RF) phase shifters to control the phase of RF carriers is a promising approach for broadband transmission because it needs to control only the phase of a continuous wave signal and not that of the broadband signal. In the proposed configuration, direct digital synthesizers (DDSs) are employed to generate phase-controlled local signals with a lower frequency than the carrier frequency. The signal is upconverted to an RF carrier frequency. More specifically, a formed beam using RF radiated signals with mm-wave or quasi-mm-wave is steered by the DDS in a precise phase-controlled manner. To confirm the feasibility of the configuration, a four-branch PAS transmitter is configured and tested in a 28-GHz operating band. The results verify that the proposed configuration is applicable to a PAS that operates in a broadband at high frequency. [ABSTRACT FROM AUTHOR]

In this paper, a novel modified Doherty power amplifier (DPA) that allows for extended output back-off (OBO) range, improved power utilization factor (PUF), and increased peak power over a broad bandwidth is proposed. It starts with an in-depth analysis of the modified DPA circuitry that first revealed the ability to control the impedances seen by the main transistor versus frequency by properly setting the magnitude and phase of the ratio between the peaks of the combining currents. This is then exploited to maximize the peak power and enhance the achievable bandwidth. Furthermore, a complex-to-real output matching network is incorporated in the auxiliary path and its parameters are carefully chosen to produce proper load modulation while satisfying the required peak combining current ratio. For validation purpose, a DPA prototype is designed to operate over the frequency range of 1.35–2.05 GHz with an OBO of 9 dB. Under the continuous-wave excitation, the DPA prototype maintained the drain efficiency (DE) of 52%–55% and 65%–75% at 9-dB OBO and peak power, respectively, over the entire targeted band. In addition, the measured peak power and PUF were about 42 dBm and higher than 0.9, respectively. The linearizability of the DPA prototype using digital predistortion (DPD) with memory was assessed while being driven with a 40-MHz carrier-aggregated signal with a peak-to-average power ratio of 8.9 dB and at an average output power of 33 dBm. When the carrier frequency is swept over the entire band, the measurement revealed an adjacent channel leakage ratio of better than −46.5 dBc after DPD with an average DE of 49.3%–53%. [ABSTRACT FROM AUTHOR]

This paper presents a broadband low-loss quadrature-hybrid-based network that enhances the phase and the amplitude matching of quadrature signals. The performance of this network is investigated, and a detailed theoretical analysis is provided. Several stages of this network can be cascaded to generate broadband balanced quadrature signals. Each stage has a loss of 0.5 dB and enhances the image rejection ratio (IRR) by approximately 8 dB. Compared with the conventional polyphase quadrature signal generation methods, the proposed network enables lower insertion loss, wider bandwidth, and reduced sensitivity to process variations. To verify the theoretical analyses, two proof-of-concept image-reject mixers are implemented in a 0.13- $\mu \text{m}$ SiGe BiCMOS technology. The first mixer achieves an average IRR of 37.5 dB across 40–76 GHz, whereas the second mixer achieves an average IRR of 33.5 dB across 40–102 GHz. The proposed network is a promising solution for broadband quadrature signal generation at millimeter-wave frequencies, as it eliminates the need for calibration and tuning. [ABSTRACT FROM AUTHOR]

Packaged integrated low-pass quasi-load insensitive (QLI) class-E matching is proposed for the realization of energy-efficient wideband Doherty and outphasing transmitters. In view of this, a dedicated QLI class-E harmonic matching technique, suitable for in-package integration has been developed, optimized, and evaluated. As proof of concept, very compact, as well as easy to assemble, dual-input load-modulating transmitters have been realized. In this paper, we focus on a QLI class-E matched wideband Doherty that provides 71% peak efficiency (±3%) at 48-dBm saturated output power and 49% (±7%) efficiency at 6-dB power backoff, over a 1200-MHz frequency span (1.4–2.6 GHz), yielding 60% fractional bandwidth (BW). When tested with single-carrier long-term evolution (LTE) signals, having a 7-dB peak-to-average ratio, average efficiency remains close to 49% (±3%) for the entire 60% fractional BW. The realized demonstrator shows excellent linearizability with adjacent channel power ratio and normalized mean square error levels below −50 dBc and −36 dB, respectively, even when operated in simultaneous dual-band LTE operation. [ABSTRACT FROM AUTHOR]

We present two monolithic microwave integrated circuit (MMIC) cryogenic broadband low-noise amplifiers (LNAs) based on the 100 nm gate length InP high-electron mobility transistor technology for the frequency range of 0.3–14 and 16–28 GHz. The 0.3–14 GHz three-stage LNA exhibited a gain of 41.6 ± 1.4 dB and an average noise temperature of 3.5 K with a minimum noise temperature of 2.2 K at 6 GHz when cooled down to 4 K. The 16–28 GHz three-stage LNA showed a gain of 32.3 ± 1.8 dB and an average noise temperature of 6.3 K with a minimum noise temperature of 4.8 K at 20.8 GHz at the ambient temperature of 4 K. This is the first demonstration of cryogenic MMIC LNA covering the whole K-band. To the best of the authors’ knowledge, the cryogenic MMIC LNAs demonstrated the state-of-the-art noise performance in the 0.3–14 and 16–28 GHz frequency range. [ABSTRACT FROM AUTHOR]

This paper presents a multi-input multi-output (MIMO) radar with simultaneously transmitted orthogonal waveforms. The radar operates in W-band, 93.5–94.5 GHz, with frequency-modulated continuous wave (FMCW) signals. The radar is designed to be capable of simultaneous transmission rather than switching transmit channels. A suitable orthogonal waveform transmission method for the FMCW radar is selected and reflected in the transceiver design. The radar consists of a transceiver, antennas, and a signal processor. The design and specifications of each module are described in detail. The transceiver consists of two transmitting channels and two receiving channels. The transmitter is designed to have high transmit power aiming at the detection and imaging of objects with small radar cross section, up to 100–150-m range. A compact horn antenna and two-channel analog-to-digital converter with a high sampling rate are designed and fabricated. The performance of each module is measured and evaluated. The performance of the radar is tested through experiments. The MIMO capability of the radar was verified through the acquisition of the range profiles with respect to four distinct signal paths by distinguishing the simultaneously transmitted orthogonal signals. The experimental results verified that the specification of the radar system is feasible for high-resolution imaging applications. [ABSTRACT FROM AUTHOR]

This paper presents a novel power combining architecture, referred to as distributed efficient power amplifier (DEPA) that mitigates the inherent bandwidth limiting factors in a Doherty power amplifier (DPA), namely, impedance inversion and load modulation, by distributing the conventional auxiliary amplifier of the DPA to multiple auxiliary subamplifiers along a broadband multisection impedance transformer. The proposed technique is demonstrated through the design, implementation, and measurement of a wideband DEPA having 8-dB output power back-off and 72% fractional bandwidth. The experimental results show a Doherty-like efficiency enhancement from 1.8 to 3.8 GHz. For the output power levels of 37.4±1.1 and 45.4±1.1 dBm, corresponding to 8-dB OBO and peak output power, the efficiency levels are between 41%–51% and 42%–62%, respectively. Furthermore, linearized modulated measurements show that the DEPA is linearizable and meets the spectral requirements for modern wireless communication systems. [ABSTRACT FROM AUTHOR]

A single-output, band selecting interposer is designed to combine three identical all-digital CMOS transmitter (Tx) chips. The open-drain CMOS Txs are flip-chip connected to the primary windings of three frequency selecting transformers realized on a single PCB interposer. The secondary windings of the three transformers are connected in series and they share a single output. Across 0.4 to 4 GHz, a peak power higher than 22.9 dBm is achieved collectively by the three sub-Txs with a drain efficiency (DE) better than 25%. The peak powers/DE of the three sub-Txs are 28.6 dBm/50%, 27.4 dBm/49%, and 24.7 dBm/34%, at 0.85, 2.1, and 3 GHz, respectively. This paper further demonstrates that the band selection can be achieved via reconfiguring the CMOS inverse Class-D switching power amplifiers. As demonstrated via continuous wave and 64-quadratic-amplitude modulation, WLAN, and LTE modulation tests, the reconfigurable Tx package exhibits high power and efficiency across all supported bands. [ABSTRACT FROM AUTHOR]

This paper attempts to develop a new automated multipoint model-order reduction (MOR) technique, based on matching moments of the system input–output function, which would be suited for fast and accurate computation of scattering parameters for electromagnetic (EM) systems over a wide frequency band. To this end, two questions are addressed. Firstly, the cost of the wideband reduced model generation is optimized by automating a greedy multipoint MOR scheme. This is achieved by introducing a new dual local-global model convergence scheme, which applies fast and reliable a posteriori error estimates to check both local model convergence, used to select the number of moments at a single expansion point, and global model convergence, used to optimally select the expansion points. Secondly, the question of optimal convergence measure is addressed by proposing an enhanced a posteriori error estimator particularly suited for scattering parameter computations for lossy EM systems. The effectiveness and efficiency of the proposed automated scheme is verified through numerical simulations using reduced-order models for examples of a bandstop dielectric resonator filter and a dielectric resonator antenna for a wide frequency band, and compared against the results obtained using the full-order model, a reduced model generated with the optimal greedy point selection algorithm, as well as the reduced-order models obtained using the reduced basis method (RBM) and the single-point second-order Arnoldi method for passive order reduction (SAPOR) method. [ABSTRACT FROM AUTHOR]

Non-Foster matching is applied to design a multi- octave broadband GaN power amplifier (PA) in this paper. The bandwidth limitation from high-Q interstage matching is overcome through the use of negative capacitor, which is realized with a negative impedance converter (NIC) using the cross-coupled GaN FETs. For high power operation over the entire bandwidth, the natural interstage matching is optimized for the upper subfrequency band and the lower subfrequency band is compensated for by the negative capacitance presented by non-Foster circuit (NFC). Detailed analysis is presented to understand the frequency and power limits of NIC circuits for PA applications. Two negative impedance matched PAs (NMPAs) are fabricated with 0.25-\mum GaN pHEMT process. The implemented PA with 2\times combining shows the output powers of 35.7–37.5 dBm with the power added efficiencies of 13–21% from 6 to 18 GHz. The 4\times combining PA achieves over 5 W output power from 7 to 17 GHz. The NFC boosts the efficiencies and power below 12 GHz to achieve broadband performance without using any lossy matching or negative feedback. To our knowledge, this is the first demonstration of NIC-based broadband amplifiers with multi-watt-level output power. [ABSTRACT FROM AUTHOR]

Recently, a new empty coaxial structure, entirely built with printed circuit boards, has been proposed. The resulting coaxial line has low radiation, low losses, high-quality factor, and is nondispersive. Up to now, this coaxial line has not been completely integrated in a planar substrate, since a working transition to a traditional planar line has not been defined yet. Therefore, in this paper, a high-quality transition from coplanar waveguide to this new empty coaxial line is proposed. With this transition, the coaxial line is completely integrated in a planar circuit board, so that it truly becomes an empty substrate-integrated coaxial line. The proposed transition has been fabricated. Both full-wave simulated and measured results show an excellent agreement. Therefore, the proposed transition is suitable to develop completely substrate-integrated components for applications in wideband communication systems that require very high quality responses and protection from external interferences. To show this fact, this new transition has been applied to integrate a high-performance empty coaxial filter in a planar substrate. The measured response of this filter is excellent, and proves the goodness of the proposed transition that has enabled, for the first time, the complete integration of an empty coaxial line in a planar substrate. [ABSTRACT FROM PUBLISHER]

A new wideband balanced power dividing/combining network with high isolation is proposed in this paper. The differential/common mode equivalent circuits of the balanced network can be easily reduced based on the matrix transformation. Two double-sided parallel-strip line (DSPSL) 180^\circ phase inverters loaded with four isolation resistors are used to realize high isolation for the power division output ports. A planar wideband balanced network with bandwidth 52.7% of (1.68–2.84 GHz, \vert Sdd21, Sdd31\vert >- 4 dB) for the differential mode and high isolation for the differential/common mode is designed and fabricated. The measured results show good agreement with the theoretical expectations. [ABSTRACT FROM PUBLISHER]

In this paper, two proposed bandwidth (BW) extension techniques are discussed and analytically analyzed. The capabilities of the proposed feedback techniques are demonstrated with two design examples of different circuitry, supported by simulation and measurement results. The first design example is a broadband low-power active balun, employing one of the presented feedback techniques. It is capable of operating with a gain of 2.2 dB and BW of more than 70 GHz. The amplitude imbalance is less than 2.4 dB, while the phase imbalance is below 7^\circ up to 60 GHz and 14^\circ up to 70 GHz, consuming a low-power of 29.7 mW. The second design example is a differential three-stage amplifier, incorporating the two techniques, where their combined performance achieves a gain of 54 dB and a 3-dB BW of 25 GHz, resulting in a gain-BW product (GBP) of 12.5 THz, with a power consumption of 180 mW from a 3.3-V supply. The chips are fabricated in a 0.35-\mum SiGe:C bipolar technology with a f_t/ f\max of 200/250 GHz. [ABSTRACT FROM PUBLISHER]

This paper presents a CMOS broadband programmable gain active balun (PGAB) that demonstrates seven digitally controlled gains with 0.5-dB gain steps separately for plus and minus output ports. The PGAB was designed and fabricated in a 130-nm RFCMOS process. For the maximum gain state, the measured gains of the plus and minus ports are 0.0 and 1.1 dB at 2 GHz. The operating frequency range is from 1.0 to 8.0 GHz by 0.3-dB gain step error, and it is from 1 to 13.0 GHz by 3-dB gain attenuation. For the maximum gain state, the measured amplitude imbalance and phase imbalance from 1 to 16 GHz are less than 1.4 dB and 4.1^\circ, respectively. The measured input return losses are better than 13.5 dB, and the output return losses are better than 18.5 dB for all controlled gain states from 1 to 16 GHz. The measured IP1dB at 7 GHz is 6.1 dBm. The measured noise figures for the plus and minus ports from 2 to 14 GHz are less than 11.2 and 10.2 dB, respectively. The supply voltages are 3.0 and 1.5 V, and the measured power consumption is 93 mW. The core area of the fabricated integrated circuit is 0.38 mm\,\times\,0.36 mm. [ABSTRACT FROM AUTHOR]

This paper presents the broadband class-C mode of operation, termed the “continuous class-C”, which is an extension of a standard class-C design but with the optimum fundamental and second harmonic terminations now forming a continuous arrangement of load impedances on the Smith chart. With the generic drain current waveform depending on the amplifier conduction angle, and by using the well-established continuous class-B (class-J) voltage waveforms, a set of closed-form equations for the fundamental and second harmonic impedances are derived. These provide a wide impedance design space to realize broadband class-C power amplifiers (PAs) with the constant output power, gain and efficiency over a significant bandwidth. The continuous class-C mode is subdivided into low- and high-power modes for which load impedance, output power and drain efficiency ratios are found and compared to those of the continuous class-B. New design spaces are graphically shown for both class-C modes. The proposed continuous class-C concepts are validated experimentally with on-wafer load pull measurements of an integrated 8×50 μm, ~ 1 W, 20 V GaN MMIC transistor. The proposed theory is also applied in simulations of power amplifiers operating in continuous class-B and continuous class-C modes. [ABSTRACT FROM AUTHOR]

In this paper, we further develop the concept of a wideband Doherty power-amplifier topology with reconfigurable efficiency. This is done by presenting new theory that - in contrast to previous work - makes it possible to analyze how the performance of the amplifier depends on the input network properties and the choice of gate bias voltages. The utility of the presented theory is demonstrated by the design and characterization of a gallium-nitride monolithic-microwave integrated-circuit amplifier designed in close agreement with the theoretical findings. Continuous-wave (CW) measurements show that the fabricated amplifier provides more than 31% power-added efficiency (PAE) at 9-dB output power back-off over a 5.8-8.8-GHz frequency range, and that the efficiency can be reconfigured as predicted by the presented theory. Modulated measurements - employing digital pre-distortion (DPD) and a 20-MHz signal with 8.5-dB peak-to-average power ratio - show more than 32% average PAE across the same 5.8-8.8-GHz frequency range. Both the CW and the modulated measurements thereby verify the wideband performance predicted by the theory. In addition, modulated measurements at 7.0 GHz without DPD show that the amplifier can provide excellent raw linearity by demonstrating -41.0-dBc adjacent channel power ratio and -34.2-dB normalized mean square error. [ABSTRACT FROM AUTHOR]

Exact synthesis of unequal power division filtering rat-race ring couplers is proposed. The power division property results from the half-symmetric core ring structure of the proposed couplers. The proposed core ring was modified from the equal power division rat-race ring in 2015 where the core ring in that circuit is fully symmetric. Due to the half-symmetry of ring and unequal power division characteristics, the signal excitation and circuit partition methods in 2015 cannot be applied. In this paper, the modified signal-excitation method and the source-division technique are proposed to reduce the original four-port rat-race ring couplers into the corresponding two-port networks. These two-port networks can be exactly synthesized by the S-domain filter synthesis method. Alternatively, the simplified design equations are proposed. Using these equations, the rat-race ring hybrid in 2015 can be transformed into the arbitrary power division rat-race ring couplers. Therefore, the final rat-race ring couplers are provided with some user-defined specifications, such as the unequal power division, the input/output impedance transformation, the center frequency, the fractional bandwidth, and the return loss level. Two fifth-order filtering rat-race ring couplers with 3- and 10-dB power division are implemented as examples; in addition, these couplers are with a center frequency of 2 GHz, a fractional bandwidth of 100%, a return loss level of 20 dB, and the input/output impedance transformation of 50/70 $\Omega $. The measured and simulated results indicate good agreement. [ABSTRACT FROM AUTHOR]

In this paper, a new design concept of Schiffman phase shifters under the operation of the second phase period in frequency domain is presented and analyzed. By investigating phase properties of the C-section structure, we first find that its second phase period is another independent and distinctive working region for Schiffman phase shifter, in addition to its first phase period. In contrast to traditional counterparts working on the first phase period, which are suitable for small phase shift from 0° to 90°, the Schiffman phase shifters on the second phase period are suitable for the large phase shift from 90° to 180°. It is because of the opposite phase variation property that the electrical length of reference line gets shortened as the phase shift value increases. Compared with the first phase period, the second phase period can achieve wider phase shift bandwidth under the same coupling degree. This feature is believed to be very useful in the limited realizable coupling degree cases. In this context, the closed-form synthesis formulas of Schiffman phase shifter on the second phase period are presented. Meanwhile, detail theoretical analysis of the phase shift bandwidth and phase deviation is carried out. In final, two Schiffman phase shifters on the first and second phase periods are designed and fabricated to validate our proposed concept and approach in the experiment. [ABSTRACT FROM AUTHOR]

Applying a spectrally efficient modulation to a wideband signal provides an extremely high data rate potential in millimeter-wave communication. In reality, wideband systems, as reported in open literature, typically suffer from insufficient signal-to-noise ratio (SNR) and thus are not able to support high-order modulation. In a recent experimental study, we have identified that a high noise floor from frequency-multiplied local oscillator (LO) sources is a major data rate limitation in wideband systems. In this paper, we present a detailed study with a mathematical model to describe the influence of the LO noise on a communication signal through frequency conversion. Followed by experimental investigations using multigigabit 64-quadrature amplitude modulation signals, measurements are performed at frequency up- and down-conversions. Both cases show SNR degradation on the frequency-converted signals as the corresponding LO noise floor increases. We provide experimental proof that the nature of the LO noise floor is white, with nearly the same amount of phase and amplitude noises. Various ways to reduce the white LO noise floor through the new hardware design are discussed providing design requirements and considerations. [ABSTRACT FROM AUTHOR]

In this paper, a new class of wideband filtering phase shifters with a pair of controllable out-of-band transmission zeroes is presented for the first time. The proposed wideband filtering differential phase shifter consists of two stub-loaded multimode resonators (SLMMR) in the main and reference branches, which can provide a constant phase shift and self-realized generalized Chebyshev filtering function with controllable transmission zeroes by properly setting the impedance ratio $R_{\mathrm {z}}$ of the loaded stub. On the one hand, the prescribed phase shift value, phase deviation, and phase shift bandwidth are deduced that basically dominated by resonant modes of SLMMR together with electrical lengths of the phase-shifting lines. On the other hand, the phase properties of transmission zeroes are systematically investigated to demonstrate that they arouse little effect on the phase shift performance, but highly improve the frequency selectivity in theoretical analysis. Based on the presented synthesis method which simultaneously considers wideband phase shift and bandpass filtering function, the circuit parameters of the entire proposed phase shifter can be synthesized with prescribed phase shift value, phase deviation, bandwidth, return loss, and transmission zero positions. Besides, the phase shift and return loss bandwidth can be determined in the design process. As design examples, two 90° wideband filtering phase shifters with different specifications are synthesized, designed, and fabricated to validate our proposed approach. [ABSTRACT FROM AUTHOR]

A compact highly efficient high-power SiGe Ka-band balanced frequency doubler is presented. Using a compact single-footprint four-way transformer input balun, wideband matching, and high fundamental rejection were achieved simultaneously. A cascode topology with very low base impedance termination was utilized for stable operation and high-voltage swing at the output. Two cascode differential pairs form a common-centroid configuration, resulting strong enhancement in output power, power-added efficiency (PAE), fundamental rejection, and robustness to process and supply variation. The proposed Ka-band cascode balanced frequency doubler was implemented in a 0.13- $\mu \text{m}$ SiGe BiCMOS technology. Measured results show 13-dBm output power with 22% peak PAE at 34 GHz for a −1-dBm input power. The 3-dB conversion gain bandwidth is from 25 to 40 GHz, fully covering Ka-band. Peak fundamental suppression is 74.5 dB at 33 GHz, and it is higher than 35 dB over Ka-band. No performance degradation is observed after 24-h RF stress test. To the author’s best knowledge, this paper has the highest efficiency, the highest output power/power density, the highest conversion gain without output buffers, and the higher or comparable fundamental rejection among any Si-based frequency doublers. Therefore, this doubler will be a promising solution for efficient and high-power local oscillator generation in 5G wireless phased-array communication system. [ABSTRACT FROM AUTHOR]

We propose a broadband eight-port forward-wave directional coupler (FWDC) with the dually symmetric structure. The novel coupler approximately achieves broadband impedance matching of the four modes. In addition, it can also provide almost constant phase differences among the four modes over a wide frequency range. Therefore, an eight-port FWDC with a broad bandwidth can be expected. Based on the Bloch–Floquet theorem, we build the equivalent models to predict the propagation properties. Also, a complete design procedure for the arbitrary power division is provided. Two samples are fabricated on Duroid substrate. Both measured and simulation results are shown for comparison and have good consistency. The achieved FBW is 47% for 0.5-dB variation. We also introduce a novel four-way phase shifter, composed of the proposed broadband eight-port FWDC with 0 dB through level and four delay transmission lines. It can support four independent pairs of the phase-shifting routes at the same time. The unique property can be applied to the three-layer broadband $8 \times 8$ Butler Matrix, as shown in this paper. It not only avoids the design of the complex crossovers, but also reduces the number of the needed phase shifters and the total size. A test sample is fabricated and measured. The obtained FBW is 36%. By properly choosing other broadband components, a compact and broadband $8 \times 8$ Butler matrix can be expected. [ABSTRACT FROM PUBLISHER]

This paper presents the design and characterization of a load modulated balanced amplifier for telecom base station applications adopting a novel mode of operation. The theory of operation is described explaining the main differences compared to Doherty amplifiers, in particular the RF bandwidth advantages and, on the other hand, the intrinsic nonlinear behavior. The specific design strategy that adopts prematching for back-off broadband matching is explained in detail. A prototype, based on 25-W GaN packaged devices, has been fabricated and measured with single tone CW and modulated signal stimulus. For CW conditions, on the 1.7–2.5-GHz band, the peak output power is between 63 and 78 W, with power added efficiency higher than 48%, 43%, and 39% at saturation, 6- and 8-dB output power back-off, respectively. With a modulated signal for Long Term Evolution the amplifier provides an average output power of around 10 W, with efficiency higher than 40%, and can be linearized by adopting a low complexity predistorter. If compared to previously published power amplifiers targeting similar power and bandwidth, the measurement shows very good performance, demonstrating the potential of this novel technique in the field of efficiency enhanced transmitters. [ABSTRACT FROM PUBLISHER]

This paper presents a novel technique for the design of broadband Doherty power amplifiers (DPAs), supported by a simplified approach for the initial bandwidth estimation that requires linear simulations only. The equivalent impedance of the Doherty inverter is determined by the value of the output capacitance of the power device, and the Doherty combiner is designed following this initial choice and using a microstrip network. A GaN-based single-input DPA designed adopting this method exhibits, on a state-of-the-art bandwidth of 87% (1.5–3.8 GHz), a measured output power of around 20 W with 6 dB back-off efficiency between 33% and 55%, with a gain higher than 10 dB. System-level measurements prove the linearizability of the designed Doherty amplifier when a modulated signal is applied. [ABSTRACT FROM PUBLISHER]