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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 broadband poly-harmonic behavioral model for microwave mixers operating in the linear regime. It is extracted from large-signal vector measurements and predicts the response with respect to an arbitrary local oscillator (LO) phase. The model is capable of estimating the performance of the converted signals and the main mixing products for an intermediate frequency that spans within an a priori defined bandwidth. This paper gives a detailed model analytical treatment along with a discussion of its properties and the description of the characterization method. The model validation is achieved by the characterization of a subharmonic mixer implemented in the hybrid technology that operates with a 2.229-GHz LO, an intermediate frequency bandwidth of 732–754 MHz, and a corresponding radio frequency bandwidth of 5.191–5.211 GHz. Independent experimental validation is achieved by an image rejection mixer composed of two nominally identical mixers, individually characterized by the proposed technique. Validation is concluded with experimental data, demonstrating the model’s capability to deal with a phase-modulated LO signal. [ABSTRACT FROM PUBLISHER]

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

This paper presents a new bandwidth tuning theory for Butterworth-response resonator filters. The presented theory shows that the bandwidth of odd-order Butterworth filters can be varied by adjusting only two interresonator coupling structures while maintaining a perfect impedance matching at the center frequency. In other words, this paper presents an analytic approach to reduce the number of tunable coupling structures when designing a bandwidth-tunable resonator filter. Theories for third- and fifth-order direct-coupled filters are discussed in detail, and it is shown that only two interresonator coupling structures are required to be tunable. In addition, for verifying the new bandwidth tuning method, a fifth-order cylindrical cavity filter has been designed, fabricated, and measured. The fabricated filter has an 11:1 bandwidth tuning range. [ABSTRACT FROM AUTHOR]

This paper presents a novel quarter-mode packaged bandpass filter with four transmission zeros (TZs) in substrate-integrated waveguide (SIW) technology. The filter has an insertion loss of 2.85 dB at 30 GHz and fractional bandwidth of 20%. The design methodology of the TZs was first demonstrated to increase the attenuations of the filter stopband. The quarter-mode SIW resonators were analyzed with high-mode suppression by properly setting their feed points. The packaged filter was consistent between the simulation and measurement results and offers the advantages of compact configuration and easy integration with other devices. Mode suppressions of up to 110 GHz were also provided. The proposed concept is attractive for designing miniaturized and high-performance-packaged filters for 3-D millimeter-wave transceiver systems. [ABSTRACT FROM AUTHOR]

This paper addresses the mechanisms of wideband power amplifiers’ efficiency degradation in comparison with their narrowband operation. It starts by identifying some possible causes for this performance degradation, showing that the baseband terminations are dominant. A detailed explanation for the efficiency degradation is then presented, considering the scenarios where the most important baseband components fall before or after the resonance imposed by the bias and matching networks. A theoretical model that is able to describe this performance degradation is also presented. Finally, the proposed theory is validated through two implemented power amplifiers with the same fundamental and harmonic terminations, but with different baseband networks, showing that an optimized bias network design can improve the efficiency performance of a PA. [ABSTRACT FROM AUTHOR]

In this paper, an extensive review of the most up-to-date papers on microwave Doherty power amplifiers is presented. The main applications are discussed, together with the employed semiconductor technologies. The different research trends, all aimed to improve the advantages of the Doherty scheme and to solve its inherent drawbacks, are presented. The first considered topic is the maximization of efficiency and/or linearity, where analog and digital techniques are exploited. Another important trend is the bandwidth enlargement of the Doherty architecture, that involves a large number of papers. Multi-band, multi-mode solutions are also considered, using either fixed or reconfigurable solutions. The final section is dedicated to the most significant Doherty integrated implementations. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of a novel class of substrate-integrated waveguide (SIW) filters, based on partially air-filled cavity resonators. Removing the dielectric in a portion of the SIW cavity allows obtaining dual-mode cavities: such cavities represent a doublet, used as the building blocks in the design of filters. A thorough modal analysis of the air-filled resonant cavity based on transmission lines’ representation and a detailed study of the doublet permit to demonstrate a full control of the operation frequency, pass bandwidth, spurious-free region, and position of the transmission zeros of the filter. This paper presents the design, fabrication, and measurement of several two-pole filters based on this concept, with the aim to show the capabilities of the proposed structure and of the design technique. A five-pole filter is also presented, to describe the extension of the proposed approach to higher order filters. [ABSTRACT FROM PUBLISHER]

This paper presents a frequency- and bandwidth-tunable bandstop filter using substrate-integrated wave- guide (SIW) resonators. For designing such a filter, this paper also presents a tunable coupling structure between a microstrip line and an SIW resonator for obtaining the bandwidth tuning capability. The coupling structure has two coupling slots between the microstrip line and the resonator, and the phase shift between the two slots determines the overall external coupling value of the resonator. This external coupling value can be controlled by making use of a phase shifter, which in turn makes it possible to adjust the bandwidth of a bandstop filter. A thorough mathematical analysis is shown using the equivalent circuit model of the presented coupling structure, and it has been verified by measuring an SIW resonator containing the presented structure. The presented tunable coupling structure has also been applied to a design of bandstop filter that can be tuned from 2.8 to 3.4 GHz. The measured results at 3.1 GHz show that the bandwidth can be tuned from 0 (all-pass) to 96 MHz reaching the attenuation level of 44 dB. [ABSTRACT FROM PUBLISHER]

This paper demonstrates a high-efficiency dual-band RF power amplifier (PA) for sub-6 GHz 5G carrier aggregation. The dual-band PA is tested with modulated signals generated by a new algorithm designed to provide realistic waveforms for carrier aggregation scenarios, allowing flexible complex (IQ) modulated sequences with arbitrary peak-to-average power ratio (PAPR), bandwidth, and band distribution. A single-stage PA is designed with a packaged 6-W transistor and a diplexer-like output matching network that separates the two bands into two outputs. It achieves an output power of 36.7 and 37.1 dBm and a power-added efficiency (PAE) of 40.4% and 39.9% at 3.5 and 5.5 GHz, respectively. Under concurrent, dual-band drive with 10-MHz, 6-dB PAPR signals and with digital predistortion applied to varying frequency notch bandwidths, an average PAE of 25.6%, a normalized mean square error of 2.4%/1.0%, and an adjacent channel power ratio of −46.8/−48 dBc in the two bands (3.5/5.5 GHz) is measured. [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 new miniaturized ultra-wideband (UWB) multilayer balanced bandpass filter (BPF) using the liquid-crystal polymer technology. The design is based on the use of two baluns and uses the transversal signal-interference concept for the realization of differential-mode (DM) passband and common-mode (CM) stopband. The broadside coupled stripline structure is adopted in this paper to realize UWB performances and pure TEM mode. The fabricated prototype is self-packaged, light in weight, and cost effective with a small footprint. The demonstrated balanced BPF achieves the excellent DM and CM responses within the entire bandwidth, centered at 6.85 GHz. The simulation and measurement results show good agreement. [ABSTRACT FROM AUTHOR]

This paper presents geometrical-based wideband circuit models for different configurations of loaded slotline and loaded coplanar waveguide (CPW). It investigates, first, the strip-loaded slotline and then extends the developed model to strip and split-ring resonator (SRR)-loaded CPW. The proposed models successfully describe the behavior of several structures of interest in the literature and provide new insights on the design procedure. They operate over the entire frequency range if higher order modes are not generated without the need for fitting parameters. This paper also presents three applications, of which the design relies on the proposed modeling methodology. They are a third order maximally flat low-pass filter with 1.4-GHz cutoff frequency, a 3-GHz slow wave structure with a slow wave factor larger than 2 in the linear range of the dispersion relation, and a balanced composite right-/left-handed SRR-loaded CPW with 100% (2.31–7.1 GHz) fractional bandwidth. Experimental results, which are in a very good agreement with the electromagnetic simulations, confirm the proposed theory. [ABSTRACT FROM AUTHOR]

In this paper, we describe the design of the first reported full W-band (75–110 GHz) power amplifier (PA) monolithic microwave integrated circuits (MMICs) based on gallium nitride technology. The discussed MMICs come in two versions. Over a bandwidth (BW) of 70–110 GHz, the three-stage PA can deliver, on average, 25.6 dBm with a power-added efficiency (PAE) of 6.5%, while the four-stage PA is able to generate 27 dBm with a PAE of 6.1%. A peak output power of 28.6 dBm is achieved at 80 GHz with a PAE of 8.6%, which corresponds to a power density of 2.6 W/mm. The significant BW was achieved partially by incorporating a novel type of broadband radial stub into the design, which can provide nearly a twofold rejection-BW improvement over the conventional version. To the best of our knowledge, no other solid-state circuit can deliver such power levels over the complete W-band. [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]

A self-biased CMOS analog mixer for ultra-wideband (UWB) applications is presented in this paper. The proposed mixer is complementary and self-biased, and has lower power consumption, superior isolation, and larger bandwidth. The proposed low-power, down conversion mixer is designed and fabricated in UMC 0.18\mu \textm CMOS technology. The measurement results show that it can operate at UWB frequencies that range from 1 to 6 GHz. The proposed mixer provides a maximum conversion gain of 13 dB, −4.5 dBm of third-order input intercept point, and a minimum double sideband noise figure of 12 dB. The maximum values of the measured local oscillator LO-to-RF, RF-to-IF, and LO-to-IF isolations are 50, 45, and 52 dB, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents a nonlinear resonator circuit based on the Duffing equation to enhance the bandwidth of wireless power harvesting and wireless power transfer systems. The Duffing resonator circuit can be implemented with passive components. In this paper, analysis of an electrical Duffing resonator is presented. The detailed discussion of the Duffing resonator’s properties is provided. As a proof of principle, a wireless power harvester employing such a nonlinear resonator has been designed and tested. It is shown that the Duffing resonator circuit enhances the bandwidth of the harvester by 2.7 times compared with a harvester using a linear resonator with the same quality factor, while achieving a similar amplitude level near the resonance frequency. Furthermore, the bandwidth of the nonlinear resonator is independent of its quality factor ( $Q$ ). [ABSTRACT FROM PUBLISHER]

This paper presents a study of the design, fabrication, and electromagnetic (EM) characterization of 3-D printed conical inductors for broadband radio frequency applications. A process flow for the design and fabrication of these components using stereolithographic 3-D printing in combination with electroless copper plating is proposed. A whole set of the samples corresponding to different geometrical parameters has been designed and fabricated using the proposed process flow. These parameters include the cone angle, the number of turns of the spiral, the metal width, and metal pitch. Experimental measurements and EM simulations have been carried out to determine the performance of conical inductors in terms of the equivalent inductance, the quality factor, and the frequency of the first resonance. The obtained results are discussed and correlated with the geometrical parameters of the samples and technological parameters of the fabrication process. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) systems working at several megahertz (MHz) are widely considered as a promising solution for a mid-range transfer of a medium amount of power. The soft-switching-based Class E power amplifier (PA) and rectifier are known to be suitable for high-frequency applications, which may potentially improve the performance of the MHz WPT systems. Meanwhile, the efficiency and output power of the Class E PA are sensitive to its loading condition, particularly when there is variation in the relative position of the coupling coils, namely a changed mutual inductance between the coils. Thus the purpose of this paper is to propose and discuss circuit and design improvements that maintain a high efficiency and output power of the MHz WPT systems over a wide range of mutual inductance, when the Class E PA and the Class E rectifier are employed. Besides, the suppression of the harmonic contents, i.e., the electromagnetic interference problem, is also considered in the circuit design. Both the simulation and experimental results show that the newly added and optimally designed $\pi $ matching network obviously improves the drops of the efficiency and output power of the Class E PA and the overall WPT system when the mutual inductance varies. The reduction of the total harmonic distortion in the input voltage of the coupling coils is also significant, from the original 52.9% to 9.6%. The circuit and design improvements discussed in this paper could serve as a general and practical solution for building high-performance MHz WPT systems. [ABSTRACT FROM PUBLISHER]

This Mini-Special Issue of this Transactions includes 6 expanded papers from the fifth IEEE MTT-S International Wireless Symposium (IEEE IWS’2018) held in Chengdu, Sichuan, China, May 6–10, 2018. [ABSTRACT FROM AUTHOR]

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

This paper is focused on the automated and unattended optimization of a type of planar wideband bandpass filters by means of aggressive space mapping (ASM). The considered filters are microstrip filters implemented through a combination of shunt connected stepped impedance resonators (SIRs) and grounded stubs coupled through admittance inverters. The most relevant and novel aspect of this paper is the fact that the filter layout is automatically generated from filter specifications, i.e., central frequency, fractional bandwidth, in-band ripple and order, without the need of any external aid to the design process. To achieve this layout generation, filter optimization has been divided into two independent ASM processes. The first one generates the filter schematic (circuit element values) providing the required specifications. This first iterative process is necessary since, due to the narrow band operation of the admittance inverters, the target specifications are achieved by compensating the effects of such narrow band operation. The purpose of the second ASM algorithm is to automatically generate the layout from the filter schematic resulting from the first ASM process. To validate the new two-step ASM optimization tool, two sets of filter specifications (inputs of the developed tool), are considered. The generated filter layouts exhibit frequency responses that satisfy the specifications, and are in excellent agreement with the responses of the schematics. [ABSTRACT FROM AUTHOR]

This paper presents a novel class of substrate integrated waveguide (SIW) filters, based on periodic perforations of the dielectric layer. The perforations allow to reduce the local effective dielectric permittivity, thus creating waveguide sections below cutoff. This effect is exploited to implement immittance inverters through analytical formulas, providing simple design rules for the direct synthesis of the filters. The proposed solution is demonstrated through the design and testing of several filters with different topologies (including half-mode SIW and folded structures). The comparison with classical iris-type SIW filters demonstrates that the proposed filters exhibit better performance in terms of sensitivity to fabrication inaccuracies and rejection bandwidth, at the cost of a slightly larger size. [ABSTRACT FROM AUTHOR]

This paper presents the design and development of highly linear, wide bandwidth mixers. We propose a linearization technique that combines the optimum drain bias condition and multiple-gated transistors for resistive mixers. An on-chip three-line edge-coupled Marchand balun is designed to have low phase and amplitude imbalance for canceling out the even order intermodulation products. Two mixer prototypes: a single-balanced (SB) mixer and a double-balanced (DB) mixer are designed to prove the concepts. The experimental results demonstrate that the SB prototype mixer has a measured conversion loss of less than 11 dB and third-order input intercept point (IIP3) range of 27–33 dBm at 15-dBm LO drive from 7 to 34 GHz. The DB mixer exhibits a conversion loss of less than 11 dB and IIP3 range of 31–35 dBm from 7–26 GHz at 17-dBm LO drive. Both prototypes achieve a high port-to-port isolation of over 30 dB within the operation bandwidth. To the best of our knowledge, the mixers have the highest linearity over the widest bandwidth ever reported. [ABSTRACT FROM PUBLISHER]

Spectral signature barcodes functional at the $S$ frequency band are presented in this paper. The barcodes are implemented by loading a coplanar waveguide transmission line by means of multiple S-shaped split ring resonators (S-SRRs), each one tuned to a different frequency. The main particularity of this paper is the fact that more than two logic states (i.e., three or four, depending on the implementation) are assigned to each resonant element. By this means, the total number of bits of the barcode (for a given number of resonators) is increased, as compared with previous approaches based on two logic states per resonator. This multistate functionality is achieved by rotating the S-SRRs. Such rotation modulates the line-to-resonator coupling intensity, and consequently the notch depth at the S-SRR fundamental resonance. Therefore, by considering three or four fixed rotation angles (or orientations) between the line axis and the S-SRR (for the tri- and four-state multiresonator barcodes, respectively), intermediate levels between the maximum and minimum attenuation are achieved. This multistate strategy only exploits a single frequency per resonant element (the fundamental one). Therefore, the data capacity per bandwidth are improved as compared with two-state-based barcodes or to multistate barcodes that use two frequencies per resonant element. As illustrative examples, two different four-state multiresonator barcodes with eight S-SRRs (providing 4^{8}= 65.536 different codes, or 16 bits) and with nine S-SRRs (equivalent to 18 bits), occupying a spectral bandwidth of 1 GHz and less than 6.75 and 8.2 cm2, respectively, are designed, fabricated, and characterized. [ABSTRACT FROM AUTHOR]

Transmitters based on nonlinear radio-frequency (RF) modulators and switched-mode power amplifiers are systems that, at least theoretically, can provide high linearity and energy-efficient generation of RF signals at the same time. However, the nonlinear memory-affected behavior remains an issue hindering practical applications. This paper shows that it is possible to model the nonlinear memory of such circuits based on time-domain observations and how to use this information in computationally efficient time-domain RF circuit models. In contrast to other works, this model covers the full bandwidth of the active device (dc–10 GHz) and it uses hierarchical data structuring to adaptively find a compact model without prior knowledge of the circuit’s memory depth. The data for this work were gained from a laboratory setup, designed to be used as an LTE transmitter for a signal bandwidth of 20 MHz at a fixed center frequency of 2.5 GHz. [ABSTRACT FROM PUBLISHER]

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

This paper analyzes the joint effects of in-phase and quadrature (I/Q) imbalance and power amplifier (PA) distortion for RF multiple input multiple output (MIMO) transmitters in the presence of crosstalk. This paper proposes candidate models for the digital predistortion of static I/Q imbalanced sources exciting a dynamic MIMO Volterra system. The proposed models are enhanced using a novel technique based on subsample resolution to account for dynamic I/Q imbalance distortions. Finally, the computational complexity of the proposed models is analyzed for implementation suitability in digital platforms. It is shown that the error spectrum for the proposed models in subsample resolution reaches the noise floor of the measurements. The proposed models achieve a normalized mean squared error of −50 dB and an adjacent channel power ratio of −57 dB for signal bandwidths upto 65 MHz and crosstalk levels ranging to −10 dB. These results demonstrate the effectiveness of the proposed techniques in the joint mitigation of I/Q imbalance and PA distortion with crosstalk for a typical $2\times 2$ MIMO telecommunication setup. [ABSTRACT FROM PUBLISHER]

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

A new cavity-based method to measure the complex permittivity of dielectric materials is presented here. The method uses a double-ridged waveguide for the cavity instead of the widely used rectangular waveguides, thus enhancing the operational frequency bandwidth by twofold. The bandwidth enhancement is advantageous when measuring the permittivities of frequency dispersive specimens. Building on the perturbation theory, this paper develops the measurement equations required for permittivity extraction. The measurement errors induced by the approximations in the perturbation theory are evaluated using numerical simulations, and the errors are quantified for different specimen sizes and dielectric constants. The experimental results are also presented. The complex permittivities of three common plastic specimens are measured at frequencies of around 3, 5, and 8 GHz using one double-ridged cavity. For comparison purposes, the same samples are also measured using two rectangular cavities operating in the S- and X-bands. Good agreement in the measured permittivity values is observed. [ABSTRACT FROM PUBLISHER]

These instructions give guidelines for preparing papers for this publication. Presents information for authors publishing in this journal. [ABSTRACT FROM AUTHOR]

This paper presents three millimeter-wave (mm-wave) continuous-mode power amplifiers (PAs) for fifth-generation (5G) MIMO applications, including a two-stage differential continuous-mode Class-F−1 PA in 130-nm SiGe process, a single-stage differential continuous-mode hybrid Class-F/F−1 PA in 45-nm SOI CMOS process, and a two-stage differential continuous-mode hybrid Class-F/F−1 PA in 45-nm SOI CMOS process. The first PA design covers 19–29.5 GHz, while the other two designs cover 23–41 GHz, all covering multiple 5G bands (24/28/37/39 GHz). All the presented PA designs are based on a proposed transformer-based continuous-mode harmonically tuned PA output network. This network provides proper harmonic impedance terminations for the fundamental, second-order, and third-order harmonic impedances, which supports continuous-mode Class-F−1 or hybrid Class-F/F−1 PA operations to achieve ultrawide bandwidth yet high efficiency. The first PA design achieves a wide $P_{\mathrm {sat}}~1$ -dB bandwidth of 19–29.5 GHz (43.3%) and high peak power-added efficiency (PAE) (43.5%). The second design achieves an ultrawide $P_{\mathrm {sat}}~1$ -dB bandwidth of 23.5–41 GHz (53.3%) and high peak PAE (46%). Moreover, it achieves 43.4% PAE and 18.6-dBm $P_{\mathrm {sat}}$ at 27 GHz, 40.2% PAE and 18.6-dBm $P_{\mathrm {sat}}$ at 37 GHz, and 41.2% PAE and 18.5-dBm $P_{\mathrm {sat}}$ at 39 GHz, respectively. The third PA design also achieves an ultrawide $P_{\mathrm {sat}}~1$ -dB bandwidth of 23.5–41 GHz (53.3%) and high peak PAE (43.2%). It achieves 43% PAE and 18.9-dBm $P_{\mathrm {sat}}$ at 27 GHz, 37% PAE and 19-dBm $P_{\mathrm {sat}}$ at 37 GHz, and 36% PAE and 18.9-dBm $P_{\mathrm {sat}}$ at 39 GHz, respectively. Extensive 64-/256-QAM modulation tests demonstrate the high PA linearity. Our proposed PA designs outperform the reported mm-wave silicon-based 5G PAs in terms of high efficiency over an ultrawide bandwidth. [ABSTRACT FROM AUTHOR]

This paper presents a frequency-agile in-band full-duplex (FD) receiver based on a switched-capacitor continuous-mode vector modulator (VM). The passive VM presented in this paper provides simultaneous downmixing, attenuation, and phase shifting and is used to generate a baseband canceler signal for self-interference (SI) cancelation. A prototype FD receiver is implemented in CMOS 130 nm technology. The receiver is tunable from 0.1 to 0.95 GHz. In FD mode at 900 MHz, the receiver has an effective input-referred third-order intercept power (IIP3) of +7 dBm, SI-to-noise-and-distortion-ratio (SINDR) of ≈ +65.3 dB at −27.5 dBm SI in 15 MHz bandwidth, and noise figure (NF) degradation of less than 1 dB. [ABSTRACT FROM AUTHOR]

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

This paper presents the first demonstration of nanowatt-level CMOS wakeup receiver (WuRx) front ends (FEs) that utilize microelectromechanical system (MEMS)-based matching networks (MNs). The first FE uses a fully MEMS-based MN (MMN) that operates at 88.8 MHz. It consists of a large array of lithium niobate resonators that are fabricated on the same die. Measurements of the integrated WuRx FE with the MMN indicate that its loaded voltage gain achieves a bandwidth of 0.78 MHz with a quality factor of 114. The second FE uses a hybrid MN (HMN) that operates at 457 MHz. It consists of an aluminum nitride laterally vibrating resonator as well as eight discrete inductors and capacitors surrounding the MEMS device. Measurements of the integrated WuRx FE with the HMN indicate that it achieves a sensitivity of −54 dBm with 7 nW of average dc power consumption without a digital correlator. [ABSTRACT FROM AUTHOR]

In this paper, a novel triplexer using the substrate-integrated suspended line technology is proposed. Two matching circuits are designed to connect the three filter channels for the triplexer construction. The used bandpass filters are composed of a low-pass filter and a high-pass filter, and they have advantages of high controllability and low insertion loss. For the proposed triplexer, two adjacent filter channels compose a duplexer. Based on the design consideration, the triplexer can be extended to a multiplexer. The proposed design is further improved by using a patterned suspended substrate for loss reduction. The triplexer achieves good isolations among the three ports and low insertion losses of 1.4/1.3/0.8 dB for the three channels of 0.8, 2.5, and 5.8 GHz, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the first experimental assessment of a highly integrated dual-band dual-polarized antenna tile designed for synthetic aperture radar (SAR) digital beamforming (DBF) satellite applications. The demonstrator described in this paper is the first comprehensive experimental validation of an RF module providing the X-band and Ka-band (9.6- and 35.75-GHz) operation with custom downconversion stages. All the antennas, transitions, and downconversion chips are integrated in the same antenna tile fabricated using a customized 15-layer high density interconnect process. The designed tile goes to the limits of the proposed technology and for the high trace density and for the size of the vertical transitions. The proposed results represent the state of the art in terms of compactness for a DBF SAR RF module even though the demonstrator was manufactured with a standard low-cost technology. The experimental assessment proves the validity of the proposed manufacturing and integration approaches showing a substantial agreement between the performance of the individual blocks and of the integrated system. [ABSTRACT FROM AUTHOR]

This paper presents, to the best of the authors’ knowledge, the first realizations of the Gysel-type power combiner/divider in ridge waveguide technology with two different configurations. Gysel combiners exhibit wider bandwidths than traditional combiners, while offering compact designs when implemented in ridge waveguide, compared with traditional waveguide combiners. In addition, Gysel combiners provide relaxed requirements on the power handling capability of the terminating loads in the case of fault conditions, which may result from imbalance between different inputs. The ridge waveguide designs offer better power handling capabilities, especially in comparison with planar designs. These advantages are shown with two different realizations, in top–bottom and side-by-side configurations, exhibiting very wide bandwidths while occupying very compact volumes. These two designs have been simulated, fabricated, and tested. Excellent test results have been obtained, confirming the validity of the concept. [ABSTRACT FROM AUTHOR]

Recently, microwave imaging under random field illuminations has attracted many interests. This paper theoretically analyzes and experimentally implements a qualitative microwave radar imaging system suitable for 2-D object. It can be customized on the demands of the desired object size and imaging resolution. Based on random illuminations generated by a minimum number of antenna elements, an analytical equation can be used to reconstruct the image of the object in near real time. The simple-structured and cost-effective imaging system can be implemented in microwave, millimeter-wave, and even sub-THz frequency bands, having promising potentials for various microwave imaging applications. [ABSTRACT FROM AUTHOR]

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

In this paper, we propose a method for designing a dual-channel balanced filter and a dual-channel balun filter based on the quad-mode dielectric resonator (DR) for the first time. By sharing one common quad-mode DR, two balanced filters or two balun filters are integrated as one single-cavity configuration, featuring compact size and high integration. A cylindrical DR with two short ends is investigated to construct the quad-mode DR. By properly arranging input and output feeding probes, two modes of the DR are only excited by the feeding probes of one channel and the other two modes are excited by that of the other channel. Accordingly, signals cannot be transmitted between the two channels, resulting in high isolation. Moreover, the required out-of-phase characteristics of the balanced and balun filters can be obtained by the inherent electromagnetic field properties of the DR without adding additional circuits, featuring a simple structure. For demonstration, a dual-channel balanced filter and a dual-channel balun filter are designed and fabricated, showing excellent balanced or balun filter performance of each channel as well as high isolation between the two channels. As compared to the other reported DR balanced and balun filters, the proposed designs exhibit a significant size reduction, which are attractive in wireless systems. [ABSTRACT FROM AUTHOR]

This paper presents the design and measurement of an interpolation-based low noise and variable gain cell (IBA-cell) in the 60-GHz band, using a 40-nm CMOS technology. The interpolation-based gain cell is designed for an innovative analog beamforming front end, where the array pattern is not only controlled in the phase domain, but also wins the flexibility in the magnitude domain. The circuit specifications are first derived for the application at 60 GHz. Techniques to combine low noise figure (NF) with variable gain tuning are presented focusing on the NF and linearity (IIP3) on the example of a 60-GHz low noise amplifier and variable gain amplifier. Subsequently, the design and measurement of the whole gain cell (IBA-cell) integrated into a single chip are reported with the technique of a cross-coupled feedback loop to reduce the phase variations over the gain tuning states and enhance the variations of IIP3. The IBA-cell achieves 15.8-dB maximum gain and 6.5-dB NF at 57 GHz with the gain tuning range from −2 to 15.8 dB and IIP3 varying from −11.3 to −16 dBm over the gain control range. The IBA-cell consumes a dc power of maximum 54 mA from 1.1 V. [ABSTRACT FROM AUTHOR]

Circular corrugated waveguides are often used in fusion applications at single, multiple, or broadband millimeter frequencies due to their low ohmic loss, expected large frequency bandwidth, and direct coupling to free-space Gaussian modes. For single-frequency corrugated waveguide systems, transmission line components can be optimized to the desired frequency. For broadband or multiple-frequency applications, this is not possible. The goal of this paper is to demonstrate that the frequency bandwidth of circular corrugated waveguides can be compromised by diffraction losses to miter bends and gaps. It is shown that if the corrugation depth differs significantly from $\lambda $ /4, a theory can substantially underpredict the gap and miter bend losses. The simulations are also shown to compare favorably to experimental measurements. To improve the transmission line performance in large frequency bandwidth systems, such as 33–165 GHz reflectometry, reducing the number of miter bends may, therefore, be necessary. For the improvement of performance in narrower frequency bandwidth or multiple-frequency systems, especially high-powered systems, wavelength-dependent techniques may be applicable. One such application is shown for a Bragg reflection technique to reduce the thermal load to insulating ceramic rings in a dc break component for multiple-frequency ITER electron cyclotron heating transmission lines. [ABSTRACT FROM AUTHOR]

This paper presents a systematic design procedure of microstrip higher order tunable bandpass filters (BPFs) that can realize a constant absolute frequency bandwidth (ABW) and transmission zeros (TZs) with the minimum number of varactors and a single controlled dc-bias voltage. To this end, intrinsic frequency dependence of interresonator couplings is employed instead of external controls, but the design has faced a difficulty of realizing ideal frequency curves of coupling coefficients at all the coupling regions, including nonadjacent couplings. To overcome such a difficulty, this paper introduces a frequency-curve shape design approach considering upward- or downward-curved convex that is dependent on the types of interresonator coupling. As illustrative examples, fourth- and sixth-order tunable BPFs are proposed and designed, starting from a coupling-matrix synthesis. Their structural parameters can be efficiently designed with the proposed design method. The frequency agility with keeping a constant ABW, acceptable low insertion loss, a good in-band return loss level, and TZs is numerically and experimentally demonstrated for both fourth- and sixth-order tunable BPFs. [ABSTRACT FROM AUTHOR]

The goal of the work presented in this paper is to demonstrate an efficient method of amplifying multiple concurrent signals over a large bandwidth using a supply modulation approach. A single-stage octave bandwidth (2–4 GHz) power amplifier (PA) with greater than 10-W output power and drain efficiency ranging from 48%–60% is presented. The amplifier is tested with several reduced-bandwidth supply modulation trajectories that are constructed as an even-termed power series of a 10-MHz LTE signal envelope. A greater than 30% point increase in $\eta _{D}$ is achieved while maintaining less than −45-dB ACPR with digital predistortion (DPD). Two 10-MHz LTE signals with 800-MHz spacing are then amplified using a similar bandwidth-reduction technique. A greater than 20% point increase in $\eta _{D}$ is seen with an improvement in linearity through the use of multidimensional DPD. The method presented here can be extended to more than two concurrent signals of arbitrary spacing for a PA with large RF bandwidth. [ABSTRACT FROM AUTHOR]

This paper presents a center frequency and bandwidth reconfiguration mechanism for waveguide microwave bandpass filters. The filters are designed to be used in the output section of a satellite communication system. While the center frequency of a bandpass filter can be tuned by changing the lengths of the filter resonators, the coupling irises as practical realizations of the impedance inverters cannot easily be adapted to a new value. The novel approach chosen in this paper is to replace the impedance inverters by a novel type of coupling structure. This coupling structure allows adjustment of the coupling by changing the length of a transmission line, which is equivalent to changing the resonant frequency of a coupling resonator. Design equations are presented to transform an impedance inverter into the proposed coupling structure. A synthesis procedure for bandwidth reconfigurable filters is proposed. The feasibility of coupling adaptation is proven based on a full-wave model of the coupling structure. The synthesis process is applied to a four-pole Chebyshev sidewall-coupled circular waveguide filter with 54- and 72-MHz bandwidth settings. The filter is built up and measured. The measured results prove that the filter can be tuned to both bandwidths over a center frequency range of 200 MHz with excellent return loss and insertion loss. [ABSTRACT FROM PUBLISHER]

This paper presents a transformer-based poly-phase network to generate fully differential quadrature signals with low loss, compact area, and high-precision magnitude and phase balance over an ultra-wide bandwidth. A fully differential high-coupling 8-port folded transformer-based quadrature hybrid serves as the basic building block for the poly-phase unit stage to achieve significant size reduction and low loss. Multiple poly-phase unit stages can be cascaded to form the multistage poly-phase network to substantially extend the quadrature signal generation bandwidth. The designs of the high-coupling transformer-based quadrature hybrid, the poly-phase unit stage, and the multistage transformer-based poly-phase network are presented with the closed-form design equations in this paper. As a proof-of-concept design, a 3-stage transformer-based poly-phase network is implemented in a standard 65 nm bulk CMOS process with a core area of 772 \mum\,\times\,925 \mum. Measurement results of this poly-phase network over 3 independent samples demonstrate that the output In-Phase and Quadrature (I/Q) magnitude mismatch is less than 1 dB from 2.8 GHz to 21.8 GHz with a passive loss of 3.65 dB at 6.4 GHz. The measured output I/Q phase error is less than 10^\circ from 0.1 GHz to 24 GHz. The effective Image Rejection Ratio (IRR) based on the measured I/Q balancing is more than 30 dB from 3.7 GHz to 22.5 GHz. The 3-stage transformer-based poly-phase network design achieves high-quality quadrature signal generation over a first-ever one-decade bandwidth together with low-loss and compact area. [ABSTRACT FROM PUBLISHER]

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

Compact balanced bandpass filters based on a combination of multisection mirrored stepped-impedance resonators and interdigital capacitors are presented in this paper. The considered filter topology is useful to achieve wide bandwidths for the differential mode, with broad stop bands for that mode, as well as very efficient common-mode suppression. By conveniently adjusting the transmission zeros for both operation modes, the differential- and common-mode stopbands can be extended up to significantly high frequencies. Filter size and this differential- and common-mode stopband performance are the main relevant characteristics of the proposed balanced filters. The potential of the approach is illustrated by the design of a prototype order-5 balanced bandpass filter, with central frequency f0 = 1.8 GHz, 48% fractional bandwidth (corresponding to 55.4% −3-dB bandwidth), and 0.04-dB ripple level. The filter is automatically synthesized by means of an aggressive space-mapping software tool, specifically developed, and two (pre- and post-) optimization algorithms, necessary to determine the transmission-zero frequencies. The designed filter is as small as 0.48\lambda g \times 0.51\lambda g , where \lambda g is the guided wavelength at the central filter frequency, and the differential-mode stopband extends up to at least 6.5 GHz with more than 22-dB rejection. The common-mode suppression is better than 28 dB from dc up to at least 6.5 GHz. [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]