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This paper deals with a low-cost method for the assembly of flexible substrate antennas and UHF RF identification silicon (Si) chips. Such a method exploits a magnetic coupling mechanism, thus not requiring for galvanic contacts between the Si chip and antenna itself. The magnetic coupling is established by a planar transformer, the primary and secondary windings of which are implemented on flexible substrate and Si chip, respectively. As a result, the Si chip can be assembled on the antenna with a mere placing and gluing process. First, the idea has been validated by theory. Electromagnetic simulations of a square heterogeneous transformer (1.0-mm side) show a maximum available power gain (MAG) of -0.4 dB at 868 MHz. In addition, the heterogeneous transformer is also quite tolerant with respect to misalignment between primary and secondary. An offset error of 150 \mu\ m reduces the MAG to -0.5 dB. A sub-optimal matching strategy, exploiting a simple on-chip capacitor, is then developed for antennas with 50-\Omega input impedances. Finally, the idea has been experimentally validated exploiting printed circuit board (PCB) prototypes. A PCB transformer (1.5-mm side) and a transformer rectifier (two-diode Dickson multiplier) have been fabricated and tested. Measurements indicates a MAG of -0.3 dB at 868 MHz for the transformer and the capability of the developed rectifier to supply a 220-\k\Omega load at 1.5 V with a -2-dBm input power. [ABSTRACT FROM AUTHOR]

In this paper, the power handling capability of microstrip filters is studied in detail. This paper is addressed from two perspectives, depending on the physical phenomenon limiting the maximum power that the microstrip filter can handle. One of these phenomena is air breakdown or corona effect, which is linked to the peak power handling capability (PPHC) of the device, and the other is the self-heating, which limits the device average power handling capability (APHC). The analysis is focused on three kinds of filtering topologies widely used both in academia and industry, such as the coupled-line, stepped impedance resonator and the dual-behavior resonator-based filters. Closed-form expressions are computed to predict both the PPHC and the APHC as a function of the geometrical parameters of the resonators integrating the filter. Guidelines are also given to extrapolate the provided computations to other filtering topologies based on other kinds of resonators. To validate this research study, three bandpass filters centered at 5 GHz have been implemented and fully characterized by means of two measurements campaigns which have been carried out, one for the PPHC and another one for the APHC. The measured results have validated the performed study and corroborated the conclusions obtained throughout this paper. [ABSTRACT FROM AUTHOR]

This paper presents a generalized geometrical equivalent circuit model for a strip-loaded coplanar waveguide (CPW) that carries the even and odd modes simultaneously. The proposed model enables the analysis, sets the design requirements, and defines the constraints of the realization of an air-bridge free all CPW Wilkinson power divider (WPD). To overcome these constraints, this paper proposes two implementations. The first one engineers the dispersion relation of the odd mode to provide a slow-wave factor that compensates the difference in the electrical lengths with the even mode, while the second implementation deploys the floating strips as electrical air-bridges. The proposed power dividers are designed to operate at 2.4 GHz. Measurements, which are in good agreement with the EM simulations, confirm the theoretical predictions. [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 investigates the source and implication of efficiency minima that is typically observed during the second-harmonic load–pull of transistor amplifiers. The study starts with the theoretical derivation of time-domain voltage and current waveforms as a function of conduction angle ($\alpha$) at the second-harmonic efficiency minima, where the output power and drain efficiency (DE) are at minimum. Thereafter, this paper unfolds a systematic re-engineering approach that is developed to recover the performance degradation and to exploit the region of efficiency minima in favor of design and implementation of high-efficiency inverse class-F power amplifiers (PAs). Interestingly, the inferences drawn from the in-depth analysis are shown to provide a simplified first-pass design approach that guarantees inverse class-F PA operation without an a priori knowledge of device parasitic elements. Theoretical postulations and simulation results are experimentally validated using an on-wafer active harmonic load–pull and a prototype design using 1.95-mm NXP gallium nitride die at a frequency of 2.6 GHz. The designed PA delivers an output power of 40 dBm with DE of 76% and gain of 12 dB at 3-dB gain compression. The measurement results confirm the theoretical framework reported in this paper. [ABSTRACT FROM AUTHOR]

In this paper, a bidirectional absorptive common-mode filter (A-CMF) is proposed to suppress the common-mode (CM) noise which would induce unwanted electromagnetic interference (EMI) and radio-frequency interference (RFI) problems. Different from the conventional CM filters (CMFs) which reflect the CM noise, the proposed A-CMF will absorb the CM wave, and thus suppress the radiation caused by reflected wave. An analysis and design method by using Smith chart with more physical insight is also proposed in this paper. To validate the proposed concept, the A-CMFs are implemented in the two-layer printed circuit boards. The absorbing frequency is selected at 2.4 GHz band where CM insertion loss is larger than 30 dB and the CM reflection loss is larger than 20 dB. With the proposed A-CMFs, more than 98% of the CM power can be eliminated. The proposed A-CMFs also provide a broadband CM suppression with fractional bandwidth lager than 126%, and a high bandwidth of differential-mode (DM) signal from dc to 7.4 GHz, which is about three times of the CM absorbing frequency. Eye diagrams are also measured to check the signal integrity, and the results show that the proposed A-CMF can still keep a good eye even under a high throughput of 7.5 Gb/s. [ABSTRACT FROM AUTHOR]

This paper presents a seven-port modulator capable of switching the polarization state of the transmitting signal. Similar to the six-port modulator, the proposed device modulates the carrier signal through the reflection coefficients generated by four variable loads. The additional seventh port allows feeding two antennas or a dual-port antenna. The loads control both the complex envelope and the polarization of the transmitted carrier signal. The mathematical model of the device, developed in this paper, is applied to analyze its performance and different modes of operation. For validation, a prototype is manufactured for a center frequency of 1575.42 MHz. It is used to generate M-quadratic-amplitude modulation at different polarizations. The signals recorded at the output of the prototype show good agreement with the values predicted by the model. [ABSTRACT FROM AUTHOR]

A class of self-isolated harmonic oscillator (SIHO) with a feedback-loop structure is able to significantly reduce the pulling effect without involving extra circuit complexity such as a buffer amplifier. In the first part of this paper, the operation principle of the SIHO is theoretically studied through equivalent circuit models and X-parameter techniques. Closed-form expressions are derived to represent the respective linear and nonlinear equivalent impedances of SIHO subnetworks perturbed by varied load and injected signals. A conventional feedback-loop oscillator structure delivering the fundamental tone is used for comparative study. Such a modeling technique reveals the physical principle and behavior parameters that have an impact on the pulling effect. The experimental verification of the SIHO operation principle and modeling is presented as the second part of this paper. To this end, a harmonic measurement and design system is proposed and implemented for the design of an exemplary SIHO, which delivers a 4-GHz signal with 16.6-dBm power, 28% dc-RF efficiency, and −136.5-dBc/Hz phase noise at 1-MHz offset. The design process does not rely on circuit simulation software packages or a prior knowledge of the large-signal model of transistors, thus demonstrating the concept of a model-free nonlinear circuit design automation based on the experimental optimization. The SIHO circuit model is validated with the measured X-parameters of its nonlinear subnetwork. [ABSTRACT FROM AUTHOR]

This paper proposed a method of synthesizing absorptive common-mode filters (A-CMFs) analytically with high absorption efficiency and two designable absorption bands. The proposed method is carried out by a novel circuit architecture and its analysis procedure. In differential mode, the integrity of the differential signals is maintained, and in common mode (CM), two absorption frequency bands can be obtained theoretically. These bands are designable with the analytical equations derived in this paper, so a dual-band or broadband A-CMF design can be easily synthesized by our proposed method. The authors also show that this method can make any one of R-CMFs “upgrade” to an A-CMF by simply adding an additional circuit, and this might be a revolutionary progress for the currently used CM-suppression techniques. To make the proposed concept more understandable, an example is used to demonstrate how the synthesizing methodology works, where a broadband A-CMF with its absorption bands located at 2.4 and 3.6 GHz is designed and implemented. Furthermore, a test sample of this A-CMF is fabricated on a four-layer printed circuit board. It is measured on a probing station, and the measured results are very similar to the simulated results. Finally, a comparison table of all the related works is given, showing that this proposed method really makes a significant improvement for A-CMF techniques. It is worth noting that this circuit design can provide a broadest 95%-absorption band to our best knowledge. [ABSTRACT FROM AUTHOR]

This paper presents a novel rectifier array for a wide dynamic range of RF-dc conversion. The rectifier array consists of multiple rectifier cells optimized for operation at different power levels and uses an adaptive power distribution method to divide the RF input power among these rectifier cells according to the RF power levels. The adaptive power distribution takes advantage of the power-dependent input impedances of the rectifier cells and is implemented with passive devices. This method both improves the rectification efficiency and minimizes the impedance mismatch as the input power level varies, and therefore, significantly enhances the dynamic range. The rectifier array can be designed using either the same type or different types of rectifying devices and can be expanded by including more cells in the network to further increase the dynamic range. In this paper, three different implementations of such rectifier array circuits are described, including a two-diode rectifier array designed with the same type of diodes, a two-diode rectifier array designed with different types of diodes, and a three-diode rectifier array with different types of diodes. The performances of these circuits are validated with measurement and compared with each other. Significant enhancement of dynamic range over conventional rectifiers is demonstrated. [ABSTRACT FROM AUTHOR]

This paper aims to present a further exploration on a new concept regarding the operation of an ultrahigh frequency (UHF) radio frequency identification (RFID) sensor tag. Exploiting the antenna of a UHF RFID tag as a temperature transducer and a UHF RFID chip with self-tuning capabilities as the means of communication, a UHF RFID tag can operate as a very low-power sensor with high read range and small size. The antenna of the tag is taking advantage of the intrinsic characteristics of the used substrate to vary its overall complex impedance according to temperature. These changes of the impedance of the antenna are leading the self-tuning circuit of the used RFID chip to self-tune and based on the value it acquires an estimation of the sensed temperature can be made. This paper also reports a design and a set of measurements of a UHF RFID tag transformed to act as a temperature sensor. This concept is further explored for the assessment of the contribution of each of the constituents of the UHF RFID tag, i.e., antenna and UHF RFID chip, to the sensing procedure. This paper is accompanied by the simulation of a designed 3-D model of the UHF RFID sensor tag and by sets of measurement of the impedances of the UHF RFID chip and of the antenna. [ABSTRACT FROM AUTHOR]

This paper presents a novel configuration for a high-Q tunable waveguide (WG) filter with a constant absolute bandwidth (BW). The key feature of this filter is that it is tuned by a single tuning element. This paper investigates the theory of coupling behavior of single septum and double septa to achieve constant absolute BW. The theory is presented for both the coupling matrix-based and inverter-based filter topologies. The filter design methodology is lucidly presented covering the design strategy adopted for interresonator coupling, input–output coupling and tuning element. The tuning mechanism of the proposed filter is explained with measurement results presented for a $Ku$ -band tunable WG filter designed at 15 GHz with a 2% BW to achieve 15% tuning range. The filter promises to be useful in emerging 5G millimeter-wave applications, where the filter size is very small to accommodate many mechanical tuning elements. Furthermore, the proposed design methodology is scalable, i.e., the tuning mechanism is independent of the filter order. [ABSTRACT FROM AUTHOR]

Multiarm slotline stubs have been used to increase the bandwidth of slotline open circuits in transitions between microstrip and slotline and between coplanar waveguide and slotline. The model used in prior papers is a series connection of the short-circuit terminated stubs, resulting in an increase in the input impedance by a factor of $N$ , where $N$ is the number of stubs. In this paper, it is shown that this model cannot be applied for slotline with finite width metal planes or coplanar stripline (CPS), because it does not account for higher order modes that are necessarily excited on the multiarm structure. This paper presents a physical explanation and model that accounts for the higher order modes on the structure and explains how the multiarm finite width slotline/CPS stub structure increases the bandwidth of the transitions between slotline and other transmission lines. With the correct model presented in this paper, it is expected that improved slotline or CPS circuits can be developed. [ABSTRACT FROM AUTHOR]

This paper presents a new asymmetric Class-F−1/F Doherty power amplifier (DPA) consisting of a Class-F−1 carrier amplifier and a Class-F peaking amplifier. The asymmetric current waveform due to different harmonic loading conditions offers an asymmetric fundamental current in load modulation region, ensuring an improvement in the performance at the peak output power. In this paper, improvements in the large signal performances, such as the output power and efficiency, are analyzed using the derived fundamental current models. For verification, a 2.4-GHz GaN Class-F−1/F DPA was designed and fabricated. The designed Class-F−1/F DPA achieves a peak output power of 44 dBm with a peak drain efficiency (DE) of 86.7%. Using a local thermal equilibrium 10-MHz signal with a 6.6-dB peak-to-average power ratio, the Class-F−1/F DPA achieves an average output power of 37.3 dBm with a DE of 68% at a supply voltage of 28 V. The measured adjacent channel leakage power ratio with a digital predistortion is below −50 dBc. [ABSTRACT FROM AUTHOR]

The maximum efficiency point of an inductive power link depends on its load power consumption and the distance between the transmitter and the receiver. Matching networks (MNs) and adjustable ac–dc converters have been proposed in the literature as a means to achieve and track this maximum efficiency point. Most of the published papers in inductive power transmission only use one of these two methods without considering a joint design. In this paper, we analyze and compare both methods proposing a general joint design which exploits the advantages of each method. A proof-of-concept system was developed following the proposed flow, built and tested. This system, with a regulated output voltage, presents improvements in measured efficiencies of up to 80% (from 9.2% to 16%) at the largest distances, thus maximizing the distance range. The same approach can be used to maximize output dc voltage, instead of the link efficiency. The proposed system using our designed MN achieved a maximum output voltage that was 90% higher (from 1.36 to 2.59 V) than the case where only a step-up converter was used. [ABSTRACT FROM AUTHOR]

In this paper, a design methodology for miniaturized cavity filters in a slow wave substrate-integrated waveguide technology is presented. It is applied in the context of ladder coupling scheme with a slow wave effect produced by a periodic arrangement of blind via holes. By taking into account the intrinsic periodicity of the structure during the synthesis, this paper aims at achieving a better filter response in terms of bandwidth and return loss, as well as providing a systematic approach for the via holes arrangement. In addition, a segmentation technique combined with the use of polynomial fittings is introduced to provide a fast and accurate design. As an illustration, a bandpass filter of 1-GHz bandwidth centered at 11 GHz is designed, fabricated, and measured. A good agreement between simulations and measurements is obtained. [ABSTRACT FROM AUTHOR]

The general coupling matrix representation of bandpass filter (BPF) circuits is a widely used technique that has simplified the analysis and optimization of complex microwave filters. In this paper, we demonstrate a novel application of the general coupling matrix for modeling wireless power-transfer (WPT) systems based on the BPF model of magnetically coupled resonators. Compared to other methods of WPT analysis, our model simplifies accommodation of complex loads and provides direct expressions for impedance matching (IM) in WPT systems. Using this tool, we achieve optimal IM for two resonator systems with a complex load, thus achieving the greatest possible power-transfer efficiency (PTE). Furthermore, our model reveals additional design constraints for optimizing PTE in coupled resonator systems exhibiting low quality factor and small interresonator coupling. Overall, this paper introduces a new, versatile framework for the analysis and optimization of coupled resonator WPT systems. Experimental results are presented, verifying the optimal IM design process. [ABSTRACT FROM PUBLISHER]

In this paper, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the noninfinity output impedances of peaking stage. Specifically, the carrier PA of the designed DPA operates in a continuous class-J mode when the peaking PA is in the OFF-state, where the output impedance of the peaking PA has some influences on the carrier PA. When the peaking transistor is in the OFF-state, the load impedance variation of the carrier transistor versus noninfinity peaking impedance is presented in this contribution. The proposed method surmounts the back-off drain efficiency deterioration of DPAs at two side working bands through elaborately processing the noninfinity peaking impedance. This paper also presents a method to derive the required OFF-state output impedance of the peaking stage by the carrier PA in a symmetrical broadband DPA. A broadband CM-DPA working over 1.6–2.7 GHz (bandwidth of 51%) is designed and fabricated for interpreting our theories. The simulated load trajectory of the carrier transistor is in line with the design space of continuous class-J mode. Under continuous wave excitation, experimental results show the drain efficiencies of 46.5%–63.5% at 6-dB output back-off power levels and 56%–75.3% at peaking power levels. The maximum output power of this DPA is 43.8–45.2 dBm with a gain of 9.4–11.5 dB across the whole working band. Furthermore, a 20-MHz LTE modulated signal with a peak-to-average power ratio of 7.4 dB is also applied to the fabricated CM-DPA at 2.2 GHz. At an average output power of 37.5 dBm, measurement results show the adjacent channel power ratios of −30.2 and −50.1 dBc before and after digital predistortion, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents an octave-bandwidth load modulated balanced amplifier (LMBA) that operates directly on a single modulated RF input. The architecture is based on the recently proposed LMBA technique, in which a control signal applied at the output isolation port of a balanced amplifier is used to modulate the apparent load impedance of the two devices comprising the balanced amplifier. In our approach, the injected control signal is used both as an active match and to dynamically load modulate the main devices to provide efficiency enhancement at back-off, thus extending the dynamic range compared to the original LMBA formulation. In this paper, we introduce a phase-compensation technique through which the active matching and load modulation tracks the frequency-dependent optimal loading trajectory of a packaged device. The result is a load-modulation power amplifier architecture able to perform an active, modulated match over an octave bandwidth. The technique is demonstrated over 1.8–3.8 GHz using packaged devices and an off-the-shelf hybrid coupler. The proof-of-concept octave RF-input LMBA has a peak CW output power of 44 dBm, with power added efficiency (PAE) over the 1.8–3.8 GHz operating frequency range of 37%–59% at peak power and 29%–45% at 6-dB output backoff. The RF-input nature of this architecture enables straightforward measurement with modulated signals; a W-CDMA signal at 3.8 GHz with 9-dB (measured) peak to average power ratio is demonstrated with adjacent channel leakage ratio of −30 dBc and average PAE of 18% for a 31-dBm average output power (2-dB backoff). [ABSTRACT FROM PUBLISHER]

Novel 2-D gray-scale inkjet printed microstrip line (MSL) terminations are presented in this paper. The proposed open-end type MSL termination is constructed of a lossy trace printed on paper and placed on a typical dielectric substrate with background. Optimal design guidelines are also discussed for attaining best absorption band given ink resistivity and termination size. Both fixed width and tapered width lines are presented, experimentally showing high absorption levels over a wide bandwidth. These simple to fabricate structures may find applications in scenarios where low-cost wideband planar terminations are needed. [ABSTRACT FROM AUTHOR]

This paper aims to effectively integrate a GaN amplifier into a high-efficiency active-antenna design. In this paper, the antenna is designed for a GaN high-electron-mobility-transistor (HEMT) impedances calculated by a load–pull simulation with a GaN nonlinear model, which contributes to a lossless design and prevents power-added-efficiency (PAE) reduction by active-antenna integration. The antenna impedance is selected to reduce the impedance-transform ratio with the GaN HEMT. In addition, the active antenna includes a second-harmonic-tuning circuit for high efficiency. The active antenna comprises antenna- and amplifier-circuit layers piled onto a Peltier unit, which has a high affinity with this cooling systems. The antenna and amplifier circuits are designed on low- and high-dielectric substrates, respectively, enabling the amplifier to be downsized and the antenna gain to be increased. Each layer is connected by a through-hole. First, the single-stage amplifier is fabricated with a maximum output power of 37.95 dBm and a maximum PAE of 62.94%. Next, the GaN active antenna is fabricated with a maximum effective isotropically radiated power of 44.61 dBm and a maximum antenna gain of 23.99 dBi. The assumed amplifier large-signal characteristics of the active antenna agree with those of the single-stage amplifier. Therefore, the amplifier and the antenna are integrated without loss. [ABSTRACT FROM AUTHOR]

This paper proposes the use of the coplanar waveguide (CPW) odd mode, also known as the parasitic slotline mode, as a design parameter. It presents a novel equivalent circuit model for the CPW cross-junction, where each CPW has two modes: the even mode, which is the conventional CPW mode also known as the coplanar mode, and the odd mode. The model is simple, intuitive, and physical-based. It can be used in different combinations including the case of slotline cross-junction. The model paves the way to design novel air-bridge free CPW applications. Among them, two are presented in this paper: CPW-to-slotline transition (balun) and Wilkinson power divider. For both applications, closed form expressions for the operating point are derived. Results are verified by EM simulations. An air-bridge free CPW power divider that combines both applications is fabricated and characterized. Simulations and measurements are in a very good agreement. [ABSTRACT FROM PUBLISHER]

In this paper, we present the performance and imaging results of an integrated single-chip CMOS-microelectromechanical systems (MEMS) scanning microwave microscope (SMM). A systematic analysis for sensitivity improvement is described in detail. We first explain why it is important to have high sensitivity for this type of microscope and then propose a systematic method to analyze and design the entire structure for better sensitivity. For this, accurate lumped models are derived for each section of the system and comparisons are made between different designs. Furthermore, a new concept based on the quality factor of the individual sections is described to give the designer a tool to improve the sensitivity of individual sections without the need to simulate or model the entire system. A high-sensitivity measurement system is also explained. Finally some measurement results are presented. While the analysis presented in this paper is for CMOS-MEMS SMM, it is applicable to any type of SMM. [ABSTRACT FROM AUTHOR]

The effect of the output impedance of peaking power amplifier (PA) on Doherty PAs (DPAs) is analyzed in this paper. In the design procedure of DPAs, the ideal case is that the output impedance of auxiliary PA is infinite at output power back-off (OPBO) level. However, it is almost impossible to realize this perfect condition in broadband DPAs. Therefore, when the output impedance of peaking path deviates from infinity, some potential effects on DPAs must be produced. In this paper, these effects are explained at the internal plane of transistors. The conclusion is that, at different normalized frequencies, there are different optimal impedance regions for the output impedance of peaking stage. This means that the noninfinite output impedances of peaking stage can enhance the performances of broadband DPAs so long as they are elaborately processed. A 1.65–2.7-GHz (48% bandwidth) broadband DPA is designed considering the effects of peaking PA. The experimental results show that this DPA obtains a drain efficiency of 41%–59.6% at 6-dB OPBO levels and a drain efficiency of 55.8%–72.2% at saturation power levels. The maximum output power across the entire operating band is 43.1–45.2 dBm with a gain of 9.0–10.2 dB. Furthermore, the designed DPA achieves an adjacent channel leakage ratio of −45.8 dBc with an output power of 36.1 dBm at 2.0 GHz after digital predistortion when it is excited by 5-MHz WCDMA signal with a peaking-to-average power ratio of 8.6 dB. [ABSTRACT FROM PUBLISHER]

This paper introduces a transmission line model analysis for dielectric-loaded self-resonant structures (SRSs). Equivalent circuit models, besides their fast computational time, usually offer some insights into the underlying physics of the electromagnetic structures, hence simplifying and improving the design and optimization criteria of these structures. A systematic approach for deriving impedance expressions of SRS on and within multi-layer dielectric media is presented. The process of extracting equivalent circuit parameters from impedance expressions is explained. The trends of equivalent circuit parameters are studied with different dielectric medium properties and various angles of incidence for an SRS with multiple resonant states highlighting the effect of changing the physical and electrical dimensions on the equivalent circuit parameters. The transmission line model responses are compared to full-wave simulation results, and model accuracy is assessed using the mean absolute error criteria. Furthermore, a new simplified method for calculating the forward transmission coefficient of an SRS within multi-layer media is proposed. This expression offers fundamental insights into the factors contributing to the $S_{21}$ response. Finally, experimental measurements for SRS embedded in a multi-layer dielectric media inside a waveguide is conducted and compared to the equivalent model with very good agreement. [ABSTRACT FROM AUTHOR]

In this paper, a generalized approach to design a multifrequency transformer with frequency-dependent complex source and load is proposed. By introducing an equivalent transformation between the perfectly matched complex-to-complex (a complex source impedance transformed to another complex load impedance) and unmatched real-to-real transformers (a real source impedance transformed to another real load impedance), the modified small reflection theory once limited to the design of the real-to-real transformer is further extended to that of the complex-to-complex transformer with more than two operating bands. Moreover, it is very useful to the design of multifrequency cascaded power amplifiers or low-noise amplifiers with compact size since its forward-stage output can be directly matched to the next-stage input. To validate the presented method, several multifrequency transformers are designed, simulated, and measured. Good agreement among the calculated, simulated, and measured results is achieved. [ABSTRACT FROM AUTHOR]

In this paper, a new scheme is proposed for a dual-band Wilkinson power divider (PD) without transmission line (TL) stubs (open- or short-circuited), or additional lumped elements (inductors and capacitors). In comparison with conventional PDs, only three additional TLs are employed. One is utilized to extend the input port, while the others are symmetrically distributed at the two branches. After applying even- and odd-mode analyses to the proposed structure, the exact closed-form design equations for a frequency ratio from 2.0 to 6.5 are derived, considering the largest realizable microstrip line impedance (150 $\Omega $). In addition, a new L-type TL with simple structure, compact size, and high design flexibility is proposed to replace the conventional TL to enhance its performance by introducing a transmission zero between the two passbands, resulting in good out-of-band rejection performance. Finally, two dual-band PDs centered at 1.0 and 3.5 GHz are designed and fabricated to verify the proposed design theory. One is based on the proposed structure, while the other incorporates a couple of L-type TLs to replace the conventional TLs. Good agreement with the simulated and measured results can be observed with a low in-band insertion loss and full ports matching. Moreover, the proposed PD also features a wide isolation band with a reference of 15-dB input port return loss. Moreover, the use of the L-type TL can introduce a good stopband between the two passbands, leading to an improved out-of-band rejection performance. [ABSTRACT FROM AUTHOR]

This paper presents a scalable E-band radar platform based on single-channel fully integrated transceivers (TRX) manufactured using 130-nm silicon–germanium (SiGe) BiCMOS technology. The TRX is suitable for flexible radar systems exploiting massive multiple-input-multiple-output (MIMO) techniques for multidimensional sensing. A fully integrated fractional-N phase-locked loop (PLL) comprising a 39.5-GHz voltage-controlled oscillator is used to generate wideband frequency-modulated continuous-wave (FMCW) chirp for E-band radar front ends. The TRX is equipped with a vector modulator (VM) for high-speed carrier modulation and beam-forming techniques. A single TRX achieves 19.2-dBm maximum output power and 27.5-dB total conversion gain with input-referred 1-dB compression point of −10 dBm. It consumes 220 mA from 3.3-V supply and occupies $3.96~\mathrm {mm^{2}}$ silicon area. A two-channel radar platform based on full-custom TRXs and PLL was fabricated to demonstrate high-precision and high-resolution FMCW sensing. The radar enables up to 10-GHz frequency ramp generation in 74–84-GHz range, which results in 1.5-cm spatial resolution. Due to high output power, thus high signal-to-noise ratio (SNR), a ranging precision of 7.5 $\mu \text{m}$ for a target at 2 m was achieved. The proposed architecture supports scalable multichannel applications for automotive FMCW using a single local oscillator (LO). [ABSTRACT FROM AUTHOR]

Reflective metasurfaces are utilized as a bridge linking propagating waves and surface waves. However, the effective constitutive parameters (permittivity and permeability) cannot be retrieved by conventional theory without transmission coefficients. In this paper, an innovative method based on a quasi-one-port network model is proposed to robustly retrieve the effective electromagnetic parameters ($\varepsilon _{\mathrm {eff}}$ , $\mu _{\mathrm {eff}}$ , $n_{\mathrm {eff}}$ , and $z_{\mathrm {eff}}$) for reflective metasurfaces with isotropic unit cells. The validity of the method is demonstrated by imping TE-polarized terahertz waves normally and obliquely (10°) on the multiple-layer unit cells. The effective boundary of the multiple-layer cells is determined by minimizing the deviation of the effective refractive indices from 0.1018 to 0.0260 using a genetic algorithm, which increases the consistency of the retrieval results. The sensitivity of the effective constitutive parameters to the accuracy of reflection coefficients and nonzero incident angle $\theta _{i}$ is also discussed. This method is beneficial for the design of reflective metasurfaces or multichannel reflectors, the coupling of spoof space plasmon polaritons, and other applications of anomalous reflection. [ABSTRACT FROM AUTHOR]

This paper demonstrates generalized code-selective filters for code-pass and code-reject signal processing at RF. A code-reject scheme using a quarter-wave ($\lambda /4$) impedance transformation is also demonstrated to overcome tradeoffs of insertion loss (IL) and linearity compared to series band-reject $N$ -path filters. A 45-nm CMOS SOI implementation consumes a power of 9.32 mW from 1 to 1.8-V supplies at the frequency of 0.35–1.1 GHz and the chip area is 1.73 mm2. The measured transmit rejection is up to 22.6 dB with 4-dB IL. The in-band third-order-intercept point (IIP3) is up to 22.6 dBm and noise figure (NF) of 4–6 dB depending on the applied codes. [ABSTRACT FROM AUTHOR]

This paper presents analytic and experimental results for high-efficiency GaN HEMT class-F and inverse class-F (class-F−1) synchronous rectifiers. The rectifier designs are based on time-reversed duals of corresponding class-F amplifiers. A detailed analysis of the power efficiency of a class-F rectifier is presented. The analysis shows that, unlike the amplifier dual, the rectifier configuration does not have significant overlap loss because of device constraints in terms of operation in quadrant III. Consequently, the power efficiency of the class-F rectifier is slightly higher than the amplifier circuit under equal source power conditions. Experimental measurements are shown, which compare the rectification efficiency of a class-F rectifier with class-F−1 rectifiers. It is shown that operation of the rectifiers under back-off conditions mimics the power efficiency of an amplifier with envelope tracking. Based on this paper, it is concluded that the class-F−1 mode has better rectification efficiency compared with that of class-F, both at peak power and under back-off conditions. [ABSTRACT FROM PUBLISHER]

The increasing use of backscatter radio for pervasive Internet-of-Things systems as a low-power and low-cost communication scheme will result in dense deployments of tags that need to operate under bandwidth (BW) constraints. Typical backscatter tags and computational radio frequency (RF) identification systems are unnecessarily limited to modulating data with “ON–OFF” switching front-ends, which leads to extensive spectrum occupancy, due to the rectangular pulses. This paper sets the foundations to overcome these limitations and proposes designs of RF front-ends that are capable of varying the tag reflection coefficient in a continuous way over time. Arbitrary waveforms can be generated to perform pulse shaping on the backscattered signals, which require significantly reduced BW. The principles presented in this paper will enable sophisticated tags to perform complex modulation schemes under BW constraints, while maintaining a very low RF front-end complexity, using a single nonlinear component such as a p-i-n diode or field-effect transistor. Migrating the idea of pulse shaping from complex power-demanding active radios to such minimal RF front-ends will complete backscatter radio as a communication scheme for simple RF tags and sensors in large-scale deployments. Each tag becomes a miniature software-defined radio that implements diverse communication schemes with increased spectral efficiency. [ABSTRACT FROM PUBLISHER]

This paper presents a tunable active bandpass filter (BPF) with adjustable transmission zeros (TZs) close to the passband for software-defined radio (SDR) applications. The RF front-end frequency selectivity is enhanced by the creation of TZs that also improve the out-of-band (OOB) input-referred third-order intercept point (IIP3). The filter is based on two-path signal cancellation and consists of a tunable BPF in parallel with two tunable bandstop filters. This combination ensures the correct amplitude and phase relationships across a wide tuning range to create adjustable TZs without sacrificing the gain of the passband. This paper presents in detail the design considerations and guidelines, as well as analysis of the filter performance in the presence of nonidealities such as parasitics and imperfect clock signal shape. The proposed filter is implemented with high- $Q~N$ -path filter blocks in a 65-nm CMOS process. The passband of the filter is tunable from 0.1 to 1.4 GHz with a 3-dB bandwidth of 9.8–10.2 MHz, a gain of 21.5–24 dB, a noise figure of 3–4.2 dB, and a total power consumption of 50–73 mW. TZs are created on both sides of the passband with a minimal offset of 25 MHz and are tunable across a 20-MHz range with up to a 60-dB rejection. The measured blocker 1-dB compression point is 8 dBm and the OOB IIP3 is 23 dBm. The reported filter provides a promising on-chip filtering solution for multistandard multifrequency SDR applications with improved interference mitigation capabilities. [ABSTRACT FROM AUTHOR]

In this paper, mode composite waveguide (MCW) is proposed, which consists of inner and outer wave-guiding duo structures. The outer structure acts as a rectangular coaxial line suitable for lower frequency operation for its compact size, while the inner structure works as a rectangular waveguide suitable for higher frequency operation thanks to its simple structure and low loss. The MCW can propagate signals in the inner waveguide with TE10 mode and/or the outer waveguide with TEM mode depending on frequency to achieve optimal performance for both low- and high-frequency operations. In this paper, the fundamental waveguide parameters and higher order modes of the duo waveguides are examined. The proposed MCW prototypes are fabricated on a triple-layer PCB structure using the emerging substrate integration techniques. The MCW is fabricated and measured through the proposed microstrip line to the inner and outer waveguide transitions, and an MCW simultaneous feeding circuit is also presented. For this simultaneous feeding circuit, the good matching is achieved from 7.5 to 10.5 GHz for the low-frequency operation and from 25 to 39 GHz for the high-frequency operation, respectively. [ABSTRACT FROM PUBLISHER]

A new synthesis for the design of a bandpass filter (BPF) with arbitrary real and/or complex termination impedances is presented in this paper. The proposed BPF can be terminated with arbitrary complex termination impedances simply by adding series transmission lines (TLs) to the first and the last coupled resonators. For design freedom, the characteristic impedances of the additional TLs can be chosen arbitrarily. Moreover, the proposed filter can be designed in either even- or odd-ordered stages using a $\lambda $ /4 stepped impedance resonator (SIR). For the validation of the proposed filter, two- and three-stage $\lambda $ /4 SIR BPFs with $Z_{S} = 30 + j10\,\,\Omega $ , $Z_{L} = 50 \,\,\Omega $ , and $Z_{S} = 50 \,\,\Omega $ , $Z_{L} = 100 + j100 \,\,\Omega $ , respectively, were designed and fabricated at the center frequency ($f_{0}$) of 2.6 GHz. The measured results are consistent with the simulation results. [ABSTRACT FROM AUTHOR]

In this paper, a new self-packaged wideband balun with the high selective bandpass filtering response and impedance transformation characteristic is presented. By virtue of circuit transformations, corresponding two-port equivalent circuit with asymmetrical port impedances is put forward. The analysis results of this two-port network exhibit that the proposed new design is able to achieve a quasi-elliptic equal-ripple response with three transmission poles and four transmission zeros. In addition, the frequency response can be directly determined according to the desired design specifications of impedance transformation ratio k, ripple fractional bandwidth (FBW), and in-band return loss RL. For validation purposes, a demonstrated wideband balun bandpass filter (BPF) working at 2.0 GHz with 50–100- $\Omega $ impedance transformation has been implemented by utilizing the multilayer liquid-crystal polymer (LCP) bonded printed circuit board (PCB) lamination technology. Theoretical, simulated, and measured results are recorded in good agreement, well verifying the design method. [ABSTRACT FROM AUTHOR]

This paper proposes a general method to design the power divider (PD) with the arbitrary filtering response. The proposed model allows coupling matrix-based filter synthesis to be adopted in the Wilkinson PD (W-PD) design so that two-order, high-order, single-band, multiband, frequency-fixed, and frequency-tunable responses are all available for the W-PD. Meanwhile, benefiting from the generalized W-PD topology, the general model can be employed to design the PD with arbitrary termination impedances (TIs), arbitrary power division ratios (PDRs), and the highly favorable isolation. To demonstrate the proposed Wilkinson filtering PD (W-FPD), a series of resonator-coupled BPFs with open-end coupling feeding line and their corresponding coupling matrices are considered and applied to the W-FPD design. Accordingly, four frequency-fixed W-FPDs are designed to achieve four fully canonical responses with a full number of transmission zeros (TZs). In addition, two highly selective frequency-agile W-FPDs with the nearly constant absolute bandwidth (ABW) are designed to achieve the very wide frequency tuning range. The excellent simulation and measurement results experimentally validate that the proposed model can be utilized to realize W-FPD with two-order, high-order, single-band, multiband, equal, unequal, equal tunable, and unequal tunable filtering responses. [ABSTRACT FROM AUTHOR]

In this paper, a novel class of differential-mode (DM) low-pass filter (LPF) with intrinsic common-mode (CM) rejection is proposed for the first time using the hybrid coplanar stripline (CPS) and the grounded CPS (G-CPS). The CPS section of the proposed DM LPF only supports DM signals and rejects its counterpart CM intrinsically. Then, the DM performances are left to be focused on in the design process of the proposed DM LPF. By utilizing the feature of high-characteristic impedance CPS and low-characteristic impedance G-CPS transmission lines, two DM LPF prototypes are designed, fabricated, and measured: one for validating the conception of DM LPF with intrinsic CM rejection and another one with the same design specifications for achieving enhanced stopband and miniaturized size simultaneously against the above-designed one. All simulated and measured frequency responses of these two DM LPFs are found to match well with each other, which further demonstrates the claimed superior performances of the proposed LPFs in terms of intrinsic CM rejection, enhanced stopband, and miniaturized size. [ABSTRACT FROM AUTHOR]

This paper presents a highly linear and power back-off efficiency-enhanced Doherty power amplifier (PA) fully integrated into CMOS. The proposed Doherty PA employs a transformer-based quadrature signal generator, multigated transistors (MGTRs) in the main PA, Class-C mode auxiliary PA, and synthesized transformer-based Doherty parallel output network with the second-harmonic control circuits. An on-chip 8-port transformer-based quadrature signal generator is designed within a single transformer footprint ($340\,\,\mu \text{m}\,\,\times 340\,\,\mu \text{m}$) and provides 0°/−90° differential signals to the main/auxiliary PAs. The MGTR in the main PA is implemented using four transistors with different sizes and biases to generate and extend a near-zero $\text {g}_{\text {m3}}$ operation region. Moreover, an on-chip transformer-based Doherty parallel output network with the second-harmonic control circuits shows higher passive efficiency compared with a conventional Doherty parallel output network and provides low second-harmonic loads to the main/auxiliary PAs. Both the proposed MGTR in the main PA and the second-harmonic control circuits in the main/auxiliary PAs suppress the third-order intermodulation distortion of the Doherty PA. This results in a substantial linearity improvement of the Doherty PA, which can support high-order modulation signals and reduce or even eliminate the need for digital predistortion (DPD). As a proof-of-concept design, a 5.8 GHz Doherty PA is implemented in a standard 55 nm bulk CMOS process. The proposed Doherty PA exhibits 27.2 dBm saturated output power with 24.5% power-added efficiency (PAE) at 5.8 GHz. The measured error vector magnitude with 40/80 MHz of 64-QAM/256-QAM is 2.5%/1.8% with 20.7/17 dBm average output power, 9.5%/5.3% average PAE, and −33.2/−36.3 dBc adjacent channel leakage ratio without any DPD. [ABSTRACT FROM AUTHOR]

This paper presents an automatic impedance transforming technique to extend the radio frequency rectifier input power range with high conversion efficiency. The rectifier employs two branches of subrectifier, each achieving impedance matching at high and low input power ranges. Then, the two branches are connected by a $\lambda/4 $ T-junction power divider. With such configuration, the input impedance of the two subrectifiers are transformed automatically, allowing the impedance matching over a wide input power range. In this way, the injected power can be optimally delivered to the subrectifiers, achieving a high efficiency over this wide input power range. This scheme manages to eliminate the power detetor for branch selection and can be applied to both single- and dual-band rectifiers with a reduced design difficulty. For validation, a single-band rectifier working at 915 MHz and a dual-band rectifier at 915/2450 MHz are implemented. Design analysis on the single- and dual-band rectifiers is carried out. The measurement results show that 68% maximum efficiency is achieved for the single-band (915 MHz) rectifier, and the input power range for the efficiency >70% of the peak efficiency is from −5 to 31 dBm. Besides, the dual-band rectifier shows 66% and 58% peak efficiencies at 915 and 2450 MHz, respectively. The input power range is from −6 to 33 dBm for the efficiency >70% of its peak value at 915 MHz, while from 10 to 32 dBm at 2450 MHz. These indicate that the input power range with high efficiency is extended. [ABSTRACT FROM AUTHOR]

Even though CMOS-based power amplifiers (PAs) provide reductions in size and cost for wireless local area network (WLAN) applications, their performances must be improved to match those of HBT-based PAs. In this paper, a design methodology for WLAN CMOS PAs is proposed to obtain broadband performances with a compact area using the wafer-level package technology. To achieve a highly linear output power with high efficiency across a 1-GHz bandwidth in a 5G-band PA, a reconfigurable interstage matching network and a broadband compact output transformer are proposed. For applications requiring a high linear transmission power, an integrated CMOS PA in a full transmitter chain must support the operation with external HBT-based PAs. A structure involving a main internal PA with an external PA driver is proposed to support the external PA mode with low-current consumption. The proposed structure does not require additional components or an output port and does not have the performance degradation of the main internal PA. The implemented 2.4G-band/5G-band CMOS PA using 40-nm CMOS technology has an average output power in the ranges of 19.1–19.2/18.6–18.8 dBm in the respective ranges of 2.4–2.5/4.9–5.9 GHz and concurrently complies with the −32-dB error vector magnitude (EVM) requirement. The power-added efficiencies (PAEs) for the 2.4G-band/5G-band CMOS PA with a −32-dB EVM is 12.9%/12.2% at 2.45/5.5 GHz. To the best of the authors’ knowledge, the presented PA exhibits the state-of-the-art minimum variation with high PAE and an output power in the range of 4.9–5.9 GHz compared to the fully integrated WiFi CMOS PAs reported thus far. [ABSTRACT FROM AUTHOR]

This paper presents a tunable reflection/transmission coefficient (TRTC) circuit based on a 45° hybrid coupler that is potentially useful for leakage cancelation purposes. The analysis of the proposed TRTC circuit shows that the circuit can cover any reflection/transmission coefficient of less than 0.5 on the Smith chart by adjusting only two variable resistors. Meanwhile, the real and imaginary parts of the reflection/transmission coefficient can be tuned independently, facilitating the use of this circuit in feedback systems. To implement the 45° hybrid coupler used in the proposed TRTC circuit, a new wideband planar topology for arbitrary phase and amplitude hybrid coupler is introduced. The circuit is analyzed and closed-form derivations for designing the proposed hybrid coupler are extracted. A prototype of the proposed 45° hybrid and TRTC circuits are fabricated and measured on 1.6-mm FR-4 PCBs at 1 GHz. The measurement results show a fractional bandwidth of 50% for the proposed 45° hybrid and a coverage radius of larger than 0.3 on the Smith chart in a frequency range of 0.8–1.2 GHz for the proposed TRTC circuit, which are well matched to the simulation results. [ABSTRACT FROM AUTHOR]

A model for integrated spiral inductors which incorporates the physically expected frequency-dependent effects modifying the device’s impedance is proposed. Moreover, it is demonstrated that the effect of resonances occurring outside the bandwidth of applicability for the device may considerably influence the performance around the peak of the Q-factor versus frequency curve. In this paper, we present the use of cascaded resonant circuits to represent the additional resonances occurring in the device to improve model accuracy up to 60 GHz. [ABSTRACT FROM AUTHOR]

In this paper, the challenges of designing distributed amplifiers at frequencies close to $f_{\text {max}}$ of transistors are tackled. By using bandpass transmission lines, the maximum operation frequency of the distributed amplifier is increased compared to low-pass transmission lines. Moreover, a novel gain-boosted cascode structure with an internal feedback is employed to cancel a part of the loss in the input line and boost the bandwidth and the highest operation frequency of the amplifier. The proposed amplifier operates up to frequencies as high as 0.67 $f_{\text {max}}$ of the transistors. Two proof-of-concept prototypes are fabricated in a 0.13- $\mu \text{m}$ SiGe process with $f_{\text {max}}$ of 210 GHz. The first prototype shows an average gain of 14.4 dB from 52 to 142 GHz (bandwidth of 90 GHz at the center frequency of 97 GHz) while the second one achieves an average gain of 18.6 dB from 48 to 135 GHz (bandwidth of 87 GHz at the center frequency of 91.5 GHz). [ABSTRACT FROM AUTHOR]

In this paper, a mixed topology for high efficiency, broadband Doherty power amplifier (DPA) is proposed. The transistor gate biases are set to deep Class-AB for the carrier device and deep Class-C for the peaking device, which enable the DPA to achieve its high efficiency. However, this biasing scheme leads to an inadequate back-off range, which in the past limited applicability. To compensate for this reduced back-off range, a “ $\pi $ -type” harmonic injection network (HIN) is integrated into the DPA thereby allowing the second harmonic to be injected between the two active devices. This achieves waveform engineering, which enhances the output power of the peaking amplifier. However, the use of this HIN leads to a reduction in bandwidth due to a mismatch at the fundamental frequency. A bandwidth compensation technique is then proposed, thereby reducing the peaking device drain impedance variation. This mitigates the reduction in bandwidth as a result of the HIN. A high-efficiency DPA is prototyped based on two identical 10-W gallium nitride HEMTs. Measurement results show that a drain efficiency of greater than 60% is achieved at 5.3–6-dB output back-off power from 1.4 to 2.1 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a new single-ended-to-balanced (SETB) impedance-transforming branch-line coupler with the arbitrary power division ratio is presented. By using the matrix transformation, the standard scattering matrix and corresponding odd- and even-mode matrices are deduced from the mixed-mode scattering matrix. A simple configuration composed of four quarter-wavelength and two half-wavelength microstrip lines is proposed to achieve desired functions of the SETB branch-line coupler with the arbitrary power division ratio and arbitrary terminated impedances. The parameter selection and design principle are given. Finally, three prototypes with different power division ratios and terminated impedances are designed to verify the theoretical prediction. Impedance matching, port isolation, and mode conversion suppression are all obtained successfully for all the three fabricated SETB branch-line couplers. The proposed configuration also offers other attractive advantages including simpler configuration and design method, lower insertion loss, and good compatibility with the planar circuit technique. [ABSTRACT FROM AUTHOR]

This paper investigates the applicability of acoustic wave devices using an interdigital transducer placed on a thin piezoelectric crystal plate to the 3–5-GHz range, where significant performance degradation was expected in surface acoustic wave (SAW) devices. Three types of the SAW-like devices were fabricated by using a KrF stepper/scanner, and their performances are compared from various aspects: 1) a 3.5-GHz resonator using a rotated $Y$ -cut LiTaO3 plate attached on a Si substrate; 2) a 5-GHz resonator using a $X$ -cut LiNbO3 plate on a Si substrate; and 3) a 5.4-GHz $A_{1}$ Lamb mode resonator on a free-standing $Z$ -cut LiNbO3 plate. It is revealed that these devices offer excellent performances even in the 3–5-GHz range. [ABSTRACT FROM AUTHOR]

This paper presents a novel design method of rat-race couplers with tunable frequency. The port equivalent impedances of a reciprocity four-port network being matched and isolated are derived by employing the even–odd mode analyses. A frequency-reconfigurable matching network (MN) transforming the port equivalent impedances to normalized unit resistance is first designed, and then the frequency-reconfigurable couplers are constructed by attaching the MN to each port of the four-port network. Based on the proposed method, two frequency-tunable rat-race couplers with power-dividing ratios of 1:1 and 2:1 are designed and measured. The measurements agree well with simulations. The measured center frequencies of the couplers with power-dividing ratios of 1:1 and 2:1 are tuned from 840 to 2480 and 840 to 2410 MHz, respectively, with a return loss of better than 15 dB and isolation of better than 20 dB. [ABSTRACT FROM AUTHOR]

A time-division duplex (TDD) transmit/receive (T/R) millimeter-wave (mm-wave) front-end comprises a power amplifier (PA), a low-noise amplifier (LNA), an antenna switch, and appropriate passive matching and combining networks. In this paper, a synthesis methodology is proposed that minimizes the overall losses by combining the PA output and the LNA input matching networks together with the T/R switch into one network. The technique improves mm-wave transceiver performance in terms of PA efficiency and LNA noise figure. The proposed T/R combiner can achieve high linearity and can handle large PA output voltage swings. The architecture can be implemented in any process which provides high integration capability. A Ka-band implementation is demonstrated using 45 nm CMOS silicon-on-insulator that includes a high power, four-stack-based PA and an inductively source-degenerated cascode-based LNA. Within the front-end, the PA achieves saturated output power of 23.6 dBm with peak power added efficiency of 28%, while the LNA achieves NF of 3.2 dB. The overall chip area is 0.54 mm2, including pads. [ABSTRACT FROM AUTHOR]

In this paper, a novel type of dynamically tunable attenuator based on graphene is proposed. This type of attenuator is composed of one or two graphene sandwich structures (GSSs) and a microstrip line. The GSSs are spread on the substrate of microstrip line near the signal strip along the direction of propagation to dissipate electromagnetic field. By the application of biased voltage, the surface impedance of graphene can be tuned, and consequently, the insertion loss of microstrip line can also be adjusted while the return loss maintains relatively low level. A transverse equivalent network and a closed form of attenuation of each attenuator are also proposed, which can be utilized to analyze the performance of attenuator with different critical parameters of graphene in detail. According to the analysis, there is a maximum value of the attenuation as the surface impedance of graphene rises from 0 to $3000~\Omega /\Box $. As an example, a prototype of each tunable microstrip line attenuator operating at gigahertz frequencies is fabricated and measured. The fabricated attenuator present favorable attenuation ranges from 3 to 15 dB, at the operating frequency from 9 to 40 GHz, and with a stable wideband attenuation corresponding to bias voltage changing from 0 to 4.0 V. [ABSTRACT FROM AUTHOR]