Search

This paper presents a new type of a low-loss miniaturized coplanar-waveguide (CPW) transmission line (TL) by employing distributed loading, capacitors and inductors, in 0.18- $\mu \text{m}$ complementary metal–oxide–semiconductor (CMOS) technology. The capacitors are realized by vertical parallel plates made of vias, and a group of open stubs inserted to the signal line, whereas the inductors are realized by high impedance lines. Then, the proposed CPW-TL is employed to design a miniaturized millimeter wave ultra-wideband low-loss Wilkinson power divider/combiner (WPD/C). The proposed distributed loading results in reducing each WPD/C arm length by more than 50% without changing its characteristic impedance and insertion loss (IL). The design is fabricated in 0.18- $\mu \text{m}$ CMOS technology and tested. The measured results show a wideband performance from dc to 67 GHz with 1-dB IL and isolation greater than 15 dB from 36 to 67 GHz. In addition, the fabricated WPD/C achieves an excellent amplitude imbalance and phase imbalance of less than 0.16 dB and 0.45°, respectively. The core chip size is $336 \times 165\,\,\mu \text{m}^{2}$ , which is almost 32.8% compact compared to the recently proposed WPD in the same technology. [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]

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]

Quasi-optical (QO) filter design is commonly based on the direct coupled bandpass filter topology with distributed resonator elements. Conventionally, prototypes with symmetrical impedance inverters are employed during synthesis, and as a result, this leads to resonators with custom lengths across the filter. This can be impractical from a QO filter implementation perspective, since spacers of arbitrary thickness may not be readily available. In this paper, we propose a novel impedance inverter equivalent network, which allows the development of prototypes where transmission lines across the filter structure to have predefined fixed lengths. Based on this technique, we developed a fourth-order QO filter prototype that composed of 2-D periodic arrays with subwavelength features. Its performance is verified with free-space measurement, and the measured results show good agreement with both full-wave and circuit simulation. Thus, it is shown that the proposed impedance inverter circuit can simplify the implementation of QO filters of higher order. [ABSTRACT FROM AUTHOR]

Benefiting from advantageous features of fast tuning, small size, and easy integration, the electronic impedance synthesizer (EIS) has been developed for on-wafer load–pull characterization systems, tunable matching networks, reconfigurable devices and systems, and so on. The previous designs of the EIS were mostly based on the empirical data instead of a closed-form design. Moreover, incomplete figures of merit (FOM) were chosen to optimize and evaluate the EIS. In this paper, we propose and present, first of all, a semiclosed-form design procedure for the distributed EIS. Then, a particle swarm optimization method is introduced to optimize the proposed nonuniformly distributed EIS, which comprises an adjusting circuit and a nonuniformly distributed circuit. Experimental results demonstrate that the proposed nonuniformly distributed structure can not only improve the Smith chart coverage but also reduce the size, compared to the uniform counterpart. The fabricated nonuniform EIS operating from 0.8 to 2.5 GHz, exhibits a good agreement between theory and measurement. Furthermore, the most comprehensive FOM are presented to evaluate the fabricated EIS. [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]

This paper presents conversion rules between ${X}$ -parameters, linearized impedance parameters, linearized admittance parameters, linearized cascade parameters, linearized scattering transfer parameters, linearized hybrid parameters, and linearized inverse hybrid parameters of a two-port network under large-signal operating conditions. The rules have been developed along with a set of equations that allow obtaining the expressions of each linearized parameter from the remaining ones. The proposed approach has been evaluated, and very good agreement has been obtained between calculated parameters and simulated ones. [ABSTRACT FROM AUTHOR]

This paper presents a closed-form solution of rough conductor surface impedance in terms of material DC conductivity and RMS roughness. Surface roughness is modeled by position-dependent conductivity at conductor-dielectric boundary to account for protrusion of rough conductor into dielectric, which was first proposed in the Gradient model. Analytic solution is obtained by approximating the Gauss cumulative distribution function, used to model the position-dependent conductivity in the Gradient model, with a square of hyperbolic tangent. Closed-form solutions are compared with numerical solutions of the Gradient model and are in good agreement up to a frequency of 100 GHz. Derived surface impedance is causal, which has been shown by numerical Hilbert transform. [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 presents a differential rectifier with high radio frequency (RF)-dc conversion efficiency over an extended input power range by using resistance compression network (RCN). The RCN is cascaded with a typical differential rectifier. It can reduce the variation range of rectifier input impedance, which changes with input power levels, and better impedance matching can be realized. Thus, the loss due to impedance mismatch is reduced, and high efficiency can be obtained in a wider input power range. First, the theoretical analysis of the RCN is carried out. Then, the detailed analysis of the rectifier input impedance and efficiency is derived in closed form. Based on the analytical results, a 915-MHz rectifier incorporating RCN is implemented. The measured results show that the RF-dc conversion efficiency keeps above 50% and 70% in the input power range 5.5–33.1 and 13.5–31.3 dBm, respectively. The maximum efficiency is 84.8%. Compared with the counterpart without RCN, the efficiency at lower input power levels is improved without degrading the peak efficiency. [ABSTRACT FROM AUTHOR]

A fully integrated transformer-based quasi-Doherty power amplifier (DPA) with an adaptive power divider (APD) is presented in this paper. A novel folded combining transformer is designed for power combining, which has smaller insertion loss than a conventional one. An APD adaptively controls the power delivered to carrier and peaking amplifiers by altering the input impedance of the peaking amplifier, which has a variable resonance frequency that changes according to the input power. Most of the power is delivered to the carrier amplifier at low incoming power, and it is divided between the carrier and the peaking amplifiers at high incoming power. With continuous wave signal at 1850 MHz, the quasi-DPA implemented with an SOI CMOS process achieves 39.8% and 44.4% power-added efficiencies (PAEs) at the first and the second peak, respectively. With wideband code division multiple access signal, it has 29.2-dBm average linear output power and a 40.47% PAE with a −33-dBc adjacent channel leakage ratio 1. With long-term evolution (LTE) signal, it delivers 27.2-dBm average linear output power and a 37.7% PAE, satisfying linearity requirements for the LTE. [ABSTRACT FROM PUBLISHER]

A recently proposed technique for enhancing near field, wireless energy transfer is to add resonant coils between the transmitter and the receiver. It also has the potential to provide a simple method for enhancing read range of near field radio frequency identification (RFID) systems. In spite of this, its application to the RFID context has not been, yet, deeply analyzed. This paper models and analyzes a half-duplex, frequency shift keying RFID system with one additional coil between the reader and the tag, considering both phases (charging and reading) of this bidirectional operation. A three-coil RFID system was designed using a commercial tag (RI-INL-R9QM widely used in cattle identification), reader (using a TMS3705), and the additional resonant coil (whose radius and quality factor were optimized). In addition, the influence of high coil quality factor is addressed for steady-state and transient response. The designed system increases almost $2.7 \times $ the original RFID read distance (from 16 to 43 cm). The analytical design and measurements data are in good agreement. The design procedure can be applied not only to other RFID systems but also to other systems that use the same channel to energize and transfer data, such as some implantable medical devices. [ABSTRACT FROM PUBLISHER]

In this paper, the concept of the transmission phase shift of an impendance-matching network (IMN) has been introduced. The generalized two-port network parameters of the matching circuit, which matches an arbitrary complex load to a different complex source impedance incorporating the transmission phase, has been derived. In general, the IMNs are electrically asymmetric; however, there exist only two distinct values of phase shifts (180° apart) for a given source and load impedance for which the networks are symmetric, irrespective of the choice of design topology. Simple examples of symmetric matching networks like single and parallel transmission lines (TLs) have been studied. The design equations of several asymmetric matching networks like the stepped-impedance, the $\Pi $ -type, and the T-type network for a given load and source impedance with desired phase shift have been derived. The concepts of allowed and forbidden regions for such matching circuits, in the impedance phase-shift plane, have been established. Two prototype impedance transformers have been fabricated and measured to establish the proposed concept. [ABSTRACT FROM AUTHOR]

This paper proposes a design approach for a broadband and high-efficiency continuous inverse Class-F ( \text CCF^-1 ) power amplifier (PA) based on a modified elliptic low-pass filtering (LPF) matching network (MN). From theoretical and practical perspectives, the importance of a swift impedance transition from the higher end of the fundamental frequency band to the lower end of the second harmonic band is discussed, when designing a broadband single-mode PA. After being compared with widely used Chebyshev LPF MNs, a modified elliptic LPF MN, which provides a sharp roll-off, is utilized to provide the required rapid transition. A step-by-step design procedure of the proposed modified elliptic LPF MN is presented. Experimental results show that a high-efficiency \text CCF^-1 PA is realized from 1.35 to 2.5 GHz (fractional bandwidth = 60%) with measured drain efficiency of 68%–82% and output power of 41.1–42.5 dBm. When stimulated by a 20-MHz LTE signal with an average output power of approximately 34.5 dBm, the proposed PA, combined with digital pre-distortion, achieved adjacent channel leakage ratios (ACLRs) below -\text 45 dBc , with average efficiency (AE) ranging from 37% to 45.8%. Similar performance is measured when the proposed PA is driven by a dual-band dual-mode modulated signal with a 100-MHz instantaneous bandwidth at a center frequency of 2.14 GHz. [ABSTRACT FROM PUBLISHER]

In this paper, a broadband upconversion image-reject mixer integrating a quadrature signal generator is presented. The polyphase networks (PPNs ) are used to convert the single-ended local-oscillator input signal to quadrature signals. A pair of inductors is added to traditional PPN to enhance the return loss performance, while optimizing the image-reject ratio. A common-emitter tranconductance using the feedforward technique is applied to a quadrature active Gilbert mixer to obtain relative high linearity, and the optical solution for high-frequency applications is given and analyzed. An active differential to single totem-pole balun is applied as the output stage, which is well matched to load impedance and can provide medium output power. Measured results show excellent performance in the designed frequency from 400 MHz to 6 GHz. [ABSTRACT FROM PUBLISHER]

This paper discusses the feasibility of a real-time active matching circuit (MC) for wireless power transfer applications, especially for biomedical systems. One prototype of low-cost real-time automatic MC, utilizing a variable circuit topology, including discrete passives and p-i-n diodes, has been implemented and the principle has been verified by measurements. One genetic algorithm was introduced to optimize the design over a wide range of impedances to match. As a result of preliminary operation verification tests, the proposed real-time MC system results in improving the transfer coefficient in the range of 10–16-cm coil separation distance a maximum of 3.2 dB automatically in about 64 ms. Similar performance improvement results were observed in additional tests under misaligned conditions, as well as for nonsymmetrical Tx–Rx coil configurations further verifying the potential applicability of the proposed system to practical biomedical devices. [ABSTRACT FROM PUBLISHER]

This paper presents a millimeter-wave tunable hybrid-transformer-based duplexer concept with dual-antenna configuration. By using orthogonal sequentially-rotated linearly-polarized antennas and the hybrid-transformer-based duplexer, the transmitter and receiver duplexes the two antennas with orthogonal circular-polarized signals. An on-chip tuning technique using magnetic coupling is introduced to improve the isolation of the duplexer in case of impedance imbalances. An alternative duplexer with a similar principle using an on-board rat-race coupler is also proposed and designed for comparison. In order to demonstrate the isolation with practical antenna connections, prototypes have been developed to integrate the on-chip duplexer and the rat-race coupler with on-board aperture-coupled microstrip antennas with sequential rotation technique. Measurement results demonstrate the orthogonal circular polarizations for the receiver and transmitter modes on both prototypes. The achieved isolation by the on-chip tunable duplexer is better than 50 dB between 30.2 and 31.2 GHz, while the achieved isolation by the rat-race version is about 20 dB in the same bandwidth. [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]

This paper presents a high power efficient broad-band programmable gain amplifier with multi-band switching. The proposed two stage common-emitter amplifier, by using the current reuse topology with a magnetically coupled transformer and a MOS varactor bank as a frequency tunable load, achieves a 55.9% peak power added efficiency (PAE), a peak saturated power of +11.1 dBm, a variable gain from 1.8 to 16 dB, and a tunable large signal 3-dB bandwidth from 24.3 to 35 GHz. The design is fabricated in a commercial 0.18-\mum SiGe BiCMOS technology and measured with an output 1-dB gain compression point which is better than +9.6 dBm and a maximum dc power consumption of 22.5 mW from a single 1.8 V supply. The core amplifier, excluding the measurement pads, occupies a die area of 500 \mu\ m\times \ 450~\mu\ m. [ABSTRACT FROM AUTHOR]

This paper presents a wideband power recycling technique for pulse-modulated polar transmitters (PMPTs). The technique allows unwanted out-of-band modulation spurs in PMPTs to be rectified and recovered back to the power supply for efficiency improvement. By configuring the power amplifiers as a balanced amplifier with dual-phase digital pulse-width modulation, the odd modulation spurs can be extracted directly from the isolation port of the output-combining quadrature coupler. Using the proposed architecture, the prototype transmitter achieved 59.1% drain efficiency at an output channel power of 26.2 dBm using a 10-MHz bandwidth long-term evolution 16-quadrature amplitude modulation test signal at 836.5 MHz. After output signal restoration by a surface-acoustic-wave filter, an output power level of 24.8 dBm and 42.8% drain efficiency were achieved while passing the spectral and receive-band-noise requirements without using any digital pre-distortion techniques. [ABSTRACT FROM AUTHOR]

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]

Recent advances in software-defined radio (SDR) technology have been pushing mixed-signal circuits to higher frequencies and forcing system integration in a single chip. These new mixed-signal devices have the capability to replace part of what was hitherto the analog side of the radio circuit, and simultaneously add several advantages. This imposes on radio engineers the need to understand and cope with these new developments. In this paper, a new framework for mixed-signal behavioral modeling is presented and discussed. It is an extension of the well-known scattering parameters, termed as D-parameters. Both linear and nonlinear methodologies are considered and analyzed. Also, application examples of this framework are presented as a way to model, characterize, and thus improve mixed-signal systems. [ABSTRACT FROM PUBLISHER]

Supplementary solutions are provided for the swapped port coupler proposed by Jeong and Kim in the above paper. It is shown that the solution given in the above paper using uncoupled line section is not the only one for the coupler operation and a more generalized solution is presented through the extended analysis. The newly proposed solutions make it possible to design the swapped port coupler based on coupled lines with variable coupling coefficients or adjustable values of the lumped capacitor. [ABSTRACT FROM PUBLISHER]

Transmitters for high peak-to-average power ratio communication are increasingly using supply modulation to improve efficiency. In addition to a dc component, the dynamic supply may contain ac components up to 500 MHz. The low-frequency (LF) dynamic impedance of the supply terminal of a power amplifier (PA) is often unknown and available nonlinear transistor models are unable to predict dynamic LF effects required for design of wideband efficient supply modulators (SMs). This paper describes a technique to calibrate and measure multi-port multi-frequency parameters of a transistor and PA under supply modulation conditions. The measurement setup is used to characterize the complex drain impedance of GaN transistors and PAs in large-signal operation at X-band with 1–500-MHz LF excitation on the drain terminal, over a range of input power levels. In addition, the LF drain impedance of a 10-GHz monolithic microwave integrated circuit PA with 4-W output power and 60% peak power-added efficiency is measured when the PA is connected to a simple switched resonant SM. The main motivation for this work is to obtain knowledge of the dynamic supply-port impedance that can enable improved PA and SM co-design. [ABSTRACT FROM PUBLISHER]

A configuration of multistrip lines mounted on a multilayer dielectric-coated elliptic cylinder is investigated in this paper. A full-wave analysis and a moment-method calculation are employed. The analysis is carried out considering the expansion of the field as a series of Mathieu functions. Both open and shielded lines are considered in the analysis. Propagation coefficients and characteristic impedances are calculated for the lines with different ellipticity. The results are verified by comparing them with those obtained from commercial software. [ABSTRACT FROM PUBLISHER]

The thru-reflect-match (TRM) calibration technique uses as standards a through connection of ports 1 and 2 of the vector network analyzer, two symmetrical highly reflecting loads, and two broadband loads (match) of impedance close to the measuring system impedance ( Z 0). The classical theory of the TRM calibration refers the calibration to the impedance of the load used as the match standard ( Z M), which is assumed as symmetrical. In practice, Z M may be frequency dependent. Moreover, as the frequency increases, the symmetry condition of the load used as match standard may become difficult to preserve, thus affecting the reference impedance definition and reducing the accuracy of the calibration. In this paper, the ABCD-parameters matrix formalism is used to introduce for the first time a generalized TRM calibration theory, allowing the use of either symmetrical or nonsymmetrical loads of arbitrary impedance as the match standard. [ABSTRACT FROM AUTHOR]

This paper presents a dual-band quadrature voltage-controlled oscillator (QVCO) using a transformer-based high-order LC-ring resonator, which inherently provides quadrature signals without requiring noisy coupling transistors as in traditional approaches, thereby achieving low phase-noise performance. Moreover, the proposed resonator shows two possible oscillation frequencies, which are exploited to realize a wide-tuning range QVCO employing a mode-switching transistor network. Due to the use of transformers, the oscillator has a minimal area penalty compared to the conventional designs. The implemented prototype in a 65-nm CMOS process achieves a continuous tuning range of 77.8% from 2.75 to 6.25 GHz while consuming from 9.7 to 15.6 mA current from a 0.6-V supply. The measured phase-noise figure-of-merit at 1-MHz offset ranges from 184 to 188.2 dB throughout the entire tuning range. The QVCO also exhibits good quadrature accuracy with 1.5^\circ maximum phase error and occupies a relatively small silicon area of 0.35 \mm^2. [ABSTRACT FROM AUTHOR]

Wireless power transfer has shown revolutionary potential in challenging the conventional charging method for consumer electronic devices. Through magnetic resonance coupling, it is possible to supply power from one transmitter to multiple receivers simultaneously. In a multiple-receiver system, the overall system efficiency highly depends on the loads’ and receivers' positions. This paper extends the conventional circuit-model-based analysis for the one-receiver system to investigate a general one-transmitter multiple-receiver system. It discusses the influence of the loads and mutual inductance on the system efficiency. The optimal loads, the input impedance, and power distribution are analyzed and used to discuss the proper system design and control methods. Finally, systems with a different number of receivers are designed, fabricated, and measured to validate the proposed method. Under the optimal loading conditions, an efficiency above 80% can be achieved for a system with three different receivers working at 13.56 MHz. [ABSTRACT FROM PUBLISHER]

This paper presents a novel concept for microwave filter design using vias (plated through-holes) in multilayered printed circuit boards. By using the concept that vias accompanied by a sufficient number of ground vias in close proximity can be approximated as transmission lines in a certain frequency range, corresponding effective impedances and phase velocities for different configurations of vias and ground vias are deduced. By controlling these transmission-line parameters, standard microwave filter methodology is applied for the design of low-pass and bandpass Chebychev filters in the frequency range of 5–20 GHz. Measurements and full-wave simulation results are presented as validation. Advantages and limitations of the proposed method are discussed. [ABSTRACT FROM PUBLISHER]

This paper presents a comprehensive theoretical study on Doherty power amplifiers (PAs) under antenna impedance mismatch. It is demonstrated for the first time that by varying the relative gain and phase of the carrier and peaking amplifiers, the PA performance degradation caused by the antenna impedance mismatch can be largely compensated. Such a compensation effect is discussed extensively for different antenna impedance conditions. Four types of Doherty PAs, i.e., three digital Doherty PAs with different degrees of flexibility and the classical analog Doherty PA, are covered in the complete theoretical analysis. To intuitively show the proposed concept, this paper presents numerical simulation results based on the theoretical analysis. In addition, measurement results on a fully integrated digital Doherty PA implemented in 65-nm bulk CMOS are demonstrated to verify our theoretical study. [ABSTRACT FROM AUTHOR]

In this paper, a dynamic stack-controlled CMOS FET RF power amplifier (PA) is developed to enhance the efficiency of the envelope tracking power amplifier (ET PA) system for low-voltage operation. The power cell used in the two-stage PA is a quadruple-stacked FET structure with dynamic stacking controller to reconfigure the power cell into the quasi-triple or quasi-double stacks according to the magnitude of the input envelope signal. The proposed power cell boosts the peak efficiency in the low VDD region by bypassing the stack entering the triode region and reoptimizing the load impedance so that all the FETs operate under the saturation and the optimum load conditions. A detailed analysis is presented to understand the gain and phase step discontinuities at the stack switching points, and the circuit techniques to equalize the gain and phase between the adjacent stack configurations are developed. The proposed two-stage stack-controlled PA is fabricated with a 0.32-\mu\ m silicon-on-insulator (SOI) CMOS process together with the envelope amplifier (EA). Full long-term evolution (LTE) characterization is performed using LTE signals with a peak-to-average power ratio (PAPR) of 6.7 dB and signal bandwidths (BW) of 10 and 20 MHz. With 10-MHz signals, dynamic stacking provides 3.5% power added efficiency (PAE) improvement over the static stack at 25.7 dBm, resulting in 47.5% PAE with 26.6-dB gain. A 20-MHz LTE test shows an overall PAE of 45.9% with an evolved universal terrestrial radio access (E-UTRA) adjacent channel leakage ratio (ACLR) of -33 dBc with memoryless digital predistortion. Even with the lower efficiency of the EA compared with the state-of-the-art results, the measured overall system efficiency with 3.4 V maximum voltage is comparable with those reported using GaAs HBT's with 5 V supplies, which clearly demonstrates the advantages of the proposed dynamic stack control. [ABSTRACT FROM AUTHOR]

This paper presents an innovative architecture to drastically enlarge the bandwidth of the Doherty power amplifier (DPA). The proposed topology, based on novel input/output splitting/combining networks, allows to overcome the typical bandwidth limiting factors of the conventional DPA. A complete and rigorous theoretical investigation of the developed architecture is presented leading to a closed-form formulation suitable for a direct synthesis of ultra-wideband DPAs. The theoretical formulation is validated through the design, realization, and test of a hybrid prototype based on commercial GaN HEMT device showing a fractional bandwidth larger than 83%. From 1.05 to 2.55 GHz, experimental results with continuous-wave signals have shown efficiency levels within 83%–45% and within 58%–35% at about 42- and 36-dBm output power, respectively. The DPA has also been tested and digitally predistorted by using a 5-MHz Third Generation Partnership Project (3GPP) signal. In particular, to evaluate the ultra-wideband and the multi-mode capabilities of the prototype, f1 =1.2~{\GHz}, f 2 =1.8~{\GHz}, and f 3 =2.5~{\GHz} have been selected as carrier frequencies for the 3GPP signal. Under these conditions and at 36-dBm average output power, the DPA shows 52%, 35%, and 52% efficiency and an adjacent channel power ratio always lower than -\43 dBc. [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]

This paper presents, for the first time, a directional coupler that allows for arbitrary power division ratios as well as arbitrary phase differences at dual frequencies of interest. Explicit design equations in terms of dual-band power-dividing ratios and phase differences will be given here and were derived based on the even- and odd-mode decomposition analysis. To illustrate the design procedure, examples will be provided and the relevant studies on the coupler's electrical parameters for a wide range of dual-band specifications and frequency ratios were conducted, by which the graphical solutions can be readily used as the further design tool. In addition, the resulting operational bandwidths are included and discussed for completeness. To validate our idea, four coupler prototypes were carried out according to the given guidelines. Excellent agreement is obtained between the measured and full-wave calculated results. The functional versatility of the proposed simple structure is well suited to applications in dual-band integrated modules, such as the beam-forming networks, for both loss and size reduction. [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]

The analysis and implementation of a dual-band direct-conversion millimeter-wave transmitter is presented. The proposed dual-band modulator uses high-impedance loads at two frequencies for the local oscillator driving amplifiers and power amplifier (PA) pre-amplifiers. To correct the amplitude and phase imbalance of the in-phase and quadrature channels at Q- and W-bands, the paper suggests a digitally controlled quadrature error correction stage to finely calibrate these errors and lower the error vector magnitude (EVM) without increasing the baseband digital-to-analog converter resolution. The transmitter is fabricated in 0.12- μm silicon-germanium BiCMOS process and occupies an area of 5.5 mm2. At 45-GHz carrier frequency, error correction improves the sideband suppression ratio (SSR) by 10 dB at 2.4-MHz IF frequency. The EVM is lowered from 3.21% to 2.38% for a 64-QAM constellation at a 2.4-Ms/s symbol rate. At 94-GHz carrier frequency, the SSR is improved from 24 to 41 dBc at 2.4-MHz IF frequency, and the EVM is lowered by more than 1% for a 16-QAM constellation at 3-Ms/s symbol rate. A dual-band PA breakout measurement indicates the peak power-added efficiency of 15% with 14-dBm maximum saturated power (Psat) at 43 GHz and 9-dBm Psat at 82 GHz is achieved. [ABSTRACT FROM AUTHOR]

This paper presents the design and analysis of novel topologies of reflective-type negative-group-delay (NGD) networks with very small signal attenuation (SA). The proposed topologies are based on short-circuited coupled lines. Theoretical analysis shows that predefined group-delay (GD) time with very small SA can be obtained due to the high characteristic impedance of a coupled line and the small coupling coefficient. Due to the very low SA characteristics of the proposed networks, the burden of compensating general-purpose gain amplifiers can be reduced and provide stable operations while integrated to RF systems. This paper also analyses performance degradation of the GD time and SA of the proposed NGD networks according to the temperature-dependent resistance variation. For an experimental validation of the proposed topologies, distributed microstrip line NGD networks (type-I and type-II) are designed, simulated, and measured for a wideband code division multiple access (WCDMA) downlink frequency operating at a center frequency of 2.14 GHz. These results show a GD time of -\ 7.27 ns with an SA of 7.43 dB for the type-I NGD network, and -\6.3 and 9.23 dB for the type II- NGD network at the center frequency, and agree closely with the simulations. To enhance the NGD bandwidth, two NGD networks with slightly different center frequencies are connected in parallel, which provides wider bandwidth than the single stage case and shows practical applicability. [ABSTRACT FROM AUTHOR]

This paper presents low-noise amplifiers (LNA) at X- and K-band frequencies in a 0.18-\mum SiGe HBT technology. A method of noise match optimization with respect to base inductance in SiGe LNA design with large transistors is proposed. The measured X- and K-band LNAs result in 1.2- and 2.2-dB mean noise figure in their frequency bands, with an associated peak gain of 24.2 and 19 dB at 8.5 and 19.5 GHz, respectively. The measured IIP3 is -\11 and -\4 dBm at 10 and 20 GHz, for a power consumption of 32.8 mW (X-band LNA) and 22.5 mW (K-band LNA). To the authors' best knowledge, these results outperform all available CMOS designs and achieve the lowest mean noise figure at X- and K-bands in any SiGe or CMOS process. The main application areas are in low-noise receivers for terrestrial communication systems and low-cost radars. [ABSTRACT FROM AUTHOR]

The behavior of a power amplifier (PA) is substantially affected by the output mismatch and mutual coupling in modern compact transmitters. To date, different works in the literature address the problem of coupling and mismatch separately, which are limited in terms of performance with a higher level of mismatch and mutual coupling. This paper identifies the reflection at the PA–antenna interface to be an effective parameter to unify the problem of mismatch and mutual coupling. Thus, a reflection-aware PA modeling and linearization method is proposed to compensate the adverse effect of mismatch and/or mutual coupling. The performance of the proposed method is investigated with a class AB and a Doherty PA under wide range of output mismatch and/or mutual coupling conditions with a 20-MHz WCDMA signal. The proposed method shows robust performance with an average adjacent channel power ratio better than 45 dBc. Such robust linearization performance under diverse output mismatch and mutual coupling conditions is highly desirable for modern and future communication systems that are subject to undergo rapid fluctuations under antenna matching and cross-coupling conditions. [ABSTRACT FROM AUTHOR]

This paper methodizes efficiency improvement during lateral misalignment for the wireless power transfer (WPT) system using two coupled semielliptic defected ground structure (DGS) resonators. We design the WPT system using a scaled value of the available mutual coupling between the resonators at perfect alignment. This scaled mutual coupling value enforces over-coupling regime, and the WPT efficiency is lower than the peak one. Then, during lateral misalignment, WPT efficiency improves until it peaks at critical coupling. Next, with further misalignment, the efficiency drops as the system enters loose coupling regime. The proposed method consists of two steps. First, we derive an analytical approach to determine the scaled mutual coupling value for efficiency design during lateral misalignment, and second, we improve the maximum obtainable efficiency by careful designing of the DGS structures’ profile. We verify the proposed method by implementing the WPT system at 300 MHz, which shows a peak efficiency of 80% for a size $D_{o} \times D_{o} = 40 \times 40$ mm2 with a transfer distance $d = D_{o}$. During misalignment, the efficiency is higher than 50% for a lateral shift up to ±0.75 $D_{o}$. [ABSTRACT FROM AUTHOR]

This paper presents the first demonstration of an active power divider operating from 100 MHz to 200 GHz. The circuit is based on a distributed architecture, where two output lines are fed replicas of the signals traveling in the shared input line. The gain element employed in the distributed divider consists of a triple-stacked cascode that exploits internal feedback to increase its equivalent transconductance. The higher transconductance toward frequency compensates the synthetic-line losses, which are the main limiting factor for applications at high frequencies of this class of circuits. A tapering of the synthetic-line impedance has also been adopted to further minimize the synthetic losses. Implemented in a high-performance 130-nm SiGe-BiCMOS technology, the system requires 300 mW of dc power consumption to provide 10 dB of gain over the 3-dB bandwidth 1–180 GHz. At 100 MHz and 200 GHz, the gain decreases to 0 dB. The presented circuit improves the state of the art for distributed power dividers implemented in any integrated circuit technology by a factor 5 for both maximum frequency of operation and bandwidth. Thanks to the triple-stacked gain cell in combination with the tapered synthetic line, the circuit reaches 10 dBm of output power at 1-dB gain compression, which is the highest reported for distributed power dividers. [ABSTRACT FROM AUTHOR]

This paper deals with the extension of the artificial material single-layer (AMSL) method, recently developed to model electromagnetically a thin conductive material using the finite-element method (FEM), to the more general case of transversally anisotropic shields. The analogy between the field equations and the multiconductor transmission line (MTL) equations is here used to calculate the admittance matrix of a thin anisotropic material. This admittance matrix is then imposed to be that of an equivalent circuit with lumped parameters. Thus, it is possible to synthetize the AMSL tensors containing the specific constants to be used in commercial software tools. The adoption of the AMSL method in FEM simulations avoids a fine discretization inside the thin conductive anisotropic material required at high frequency. Simple tests are finally carried out to validate the proposed method. [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]

This paper presents the practical realization of a power divider and a 90° hybrid directional coupler in an empty substrate-integrated coaxial line (ESICL) for C-band frequency applications. This new type of transmission line is very promising in terms of electric performance, bandwidth, integration with other planar circuits, and manufacturing simplicity. The ESICL has been designed for obtaining a wide monomode bandwidth with a characteristic impedance of 50 $\Omega $. Furthermore, an improvement of the efficient transition between the ESICL and the grounded coplanar waveguide, used as feeding line, has been also proposed. The passive devices built using this technology are reduced in mass and volume, keeping robustness, and providing a well-balanced power division, as well as reduced losses and high isolation in the whole operational bandwidth. Two prototypes have been manufactured and the experimental results are in good agreement with the simulated designs. [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]

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]

This paper presents a linear Doherty power amplifier (DPA) topology suitable for low-powered small cell and multiantenna fifth generation transceivers. The proposed topology relies on augmenting the conventional two-way DPA with a linearization amplifier (LA) in order to enhance its efficiency versus linearity tradeoff when driven with wideband modulated signals. For this, a study of the interactions between the LA and DPA circuitries is conducted, and a design strategy is developed to determine the circuit’s parameters that maximize the adjacent channel leakage ratio (ACLR) improvement while minimizing its power overhead. For validation purpose, this strategy is applied to design a proof of concept prototype with a center frequency of 800 MHz and an output peak envelope power of 12 W. Compared with the case where the LA is not integrated, more than 11-dB improvement of the ACLR was obtained at the prototype output when driven with modulated signals of up to 40 MHz of modulation bandwidth. Furthermore, an ACLR of about −45 dBc or better was maintained over a wide average power range. [ABSTRACT FROM PUBLISHER]

This paper presents a single spark-gap switch (SGS)-based high-power bipolar pulse generator (BPG) for many applications, such as high-power electromagnetic (HPEM) effect tests. Here, we propose an inverted U-shaped parallel transmission line structure to implement the single-SGS-based BPG. Unlike the previously reported BPGs based on synchronized operation of two SGSs, the proposed BPG does not require simultaneous or synchronized closure of the two switches. Detailed dimension parameters obtained by electromagnetic simulation. The proposed BPG was manufactured and tested for validation. The experimental results demonstrated that the BPG produced a bipolar pulse with a peak-to-peak amplitude of 44.9 kV and a pulsewidth of 2.27 ns, where the SGS was filled with nitrogen gas of 16 atm and the turn-ON voltage was 56 kV. For applications of HPEM effect tests, we discuss methodologies to control the amplitude and pulsewidth of generated bipolar pulses in the proposed BPG. [ABSTRACT FROM PUBLISHER]