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

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

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

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

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

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

In this paper, $N$ -way Gysel power dividers with arbitrary power-dividing ratio are studied by using node voltage and current method for the first time. Closed-form analytical equations are derived for the design of the proposed Gysel power divider with arbitrary power division on arbitrary terminated impedance. Parameters that might influence the frequency bandwidth are investigated and optimized to achieve balanced performance. For verification, 3-way and 6-way Gysel power dividers are, respectively, designed, fabricated, and measured at a center frequency of 3.45 GHz, with dividing ratio 1:1:1, 1:2:3, 1:1:1:1:1:1:1, and 1:1.2:1.2:1.5:1.5:2, respectively. Good agreements can be observed among expected, simulated, and measured results, indicating the validity of the proposed strategies. [ABSTRACT FROM AUTHOR]

In this paper, a high-efficiency Doherty power amplifier (DPA) using the complex combining load (CCL) with noninfinity peaking impedance for broadband operation is presented. By applying the CCL, the load impedance of the carrier amplifier at saturation power level can be compensated at different operation frequencies. Considering the influences of the output impedance of the peaking PA on the carrier PA, a detailed analysis of the optimal noninfinity peaking output impedance with the CCL is carried out on the whole operation frequency range. Theoretical analysis of the output power and drain efficiency (DE) reveals that the CCL can offer a new degree of freedom for extending the bandwidth of the DPA. Based on the proposed theory, a modified DPA working over the frequency band of 1.1–2.4 GHz (bandwidth of 74%) is designed and fabricated based on GaN HEMT devices. Experimental results exhibit 6-dB output back-off drain efficiencies of 43.8%–54.9% and saturated drain efficiencies of 55.4%–68% can be obtained. The saturated output power of the DPA is 43.3–45.4 dBm with a gain of 9.5–11.1 dB across the whole operation band. When driven with long-term evolution modulated signals with 6.5-dB peak-to-average power ratio, the DPA exhibits an adjacent channel leakage ratio better than −49 dBc while maintaining a DE of 44% after digital predistortion linearization. [ABSTRACT FROM AUTHOR]

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

A new microstrip balanced-to-unbalanced power divider with dual bandpass filtering response is presented in this paper. The generalized mixed-mode scattering matrix for the filtering balanced-to-unbalanced power divider is derived to guide the design. Differential-mode (DM) dual-band filtering response is analyzed under the odd-mode excitation to show that the frequency ratio ($k = f_{2}/f_{1}$) and bandwidth of these two passbands could be flexibly controlled. For the even-mode excitation, two intrinsic transmission zeros generated by additional open-ended stub are introduced, aiming to achieve the enhancement of in-band common-mode (CM) suppression. In addition, good in-band isolation and port matching are realized by introducing a grounded resistor. To validate the design concept, two prototypes centering at 1 and 2.5 GHz ($k = 2.5$), as well as 0.76 and 2.75 GHz ($k = 3.62$) are implemented following the given design procedure. Tested results of the two fabricated circuits, well agreeing with the simulated ones, exhibit high performances in terms of DM response, in-band CM suppression, port-to-port isolation, and port matching. [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]

CMOS RF switches support watt-level RF output power while enabling signal processing with high speed. Typically, RF FET switches offer a tradeoff between a power handling and modulation bandwidth. This paper investigates the cause of compression in a FET switch, and the analysis suggests the optimization of the gate driving impedance for a stacked-FET switch. A design methodology is presented to realize watt-level power handling with high fractional bandwidth (FBW). The measurements demonstrate a BPSK modulator that can handle up to 10 W with wide FBW. The high-power, low-insertion loss, and high-modulation bandwidth demonstrate record performance. [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, 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]

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 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 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]

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]

A method enabling the codesign of a high-efficiency power amplifier (PA) and a ring-resonator microstrip bandpass filter is proposed in this paper. Even–odd-mode analysis and a series of continuous modes (SCMs) are combined to realize broadband or multiband impedance matching as well as the suppression of undesired signals. The proposed codesign method can achieve both broadband and multiband frequency responses, and the designed component is relatively easy to analyze and fabricate due to its microstrip structure. For verification, a broadband and triband PA-filter components are designed and fabricated separately. The first component operates across 0.8–3.2 GHz (120%) with 39.7–42.9-dBm maximum output power and 57%–74% drain efficiency (DE). The second component, which has three passbands, covers several commercial frequencies with a measured output power of 39.6–41.3 dBm and DE from 62% to 68%. When these two components are driven by a 20-MHz long-term evolution signal with a peak-to-average power ratio of 6.2 dB, adjacent channel leakage ratios from −26.4 to −33.8 dBc and from −29.4 to −33.1 dBc are measured, respectively. [ABSTRACT FROM AUTHOR]

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

This paper presents a new kind of highly flexible frequency-agile bandpass filters (FA-BPFs) based on the novel synchronously tuned dual-mode resonator (STDR). The bandwidth (BW), BW variation tendency, passband selectivity (stopband rejection level), and frequency tuning range of the filter can be predefined individually. Benefiting from the unique characteristics of the STDR, the FA-BPF with very simple and highly flexible design/control procedures is achieved. Due to the proposed geometry, two self-adaptive transmission zeros are introduced and move with the passband. The predefined mechanism is investigated in detail, and the simple design and predefined procedures are summarized. Then, three 0.75–1.7 GHz single-band examples with elliptic response are developed to achieve three predefined absolute BWs (ABW). The design techniques and filter superiority are confirmed by the experiments. Moreover, aiming at China 2G/3G/4G cellular wireless/mobile communication system (up to band 40:0.825–2.65 GHz), a novel intrinsically switchable single-/dual-band FA-BPF is presented based on the proposed STDR. An example with a constant ABW1 dB and a fractional bandwidth1 dB (FBW1 dB is designed to validate the theory and analysis. The FA-BPF is able to operate as a highly selective dual-band FA-BPF with 0.76–1.78 GHz/1.61–2.63 GHz tuning ranges, and also can be switched to single-band operation with the continuous tuning range of 0.76–2.63 GHz. [ABSTRACT FROM PUBLISHER]

This paper presents a design strategy to enhance the bandwidth of three-stage Doherty power amplifier (DPA) with operation upto 12-dB back-off. Based on the proposed strategy, a broadband 48-W DPA is designed and implemented using packaged CREE GaN transistors. The measured drain efficiency of 50%–61.8% at 12-dB back-off and 51.9%–66.2% at 6-dB back-off is obtained over the frequency range of 600–900 MHz. Over this 300-MHz band, the drain efficiency is between 51.1% and 78% at saturation. This corresponds to 40% fractional bandwidth. The three-stage DPA is also linearized with a three carrier 15-MHz WCDMA signal with a PAPR of 10.6 dB at various frequencies within operating band and shows the output signal qualifies spectral mask specifications. [ABSTRACT FROM PUBLISHER]

This paper introduces a method giving dimensions of inline evanescent-mode ridge waveguide bandpass filters. Evanescent mode couplings are evaluated individually, without optimization of the entire filter. This is obtained through an improved network model of the evanescent-mode coupling, together with novel analytical formulas to correct the resonators slope parameters. Unlike prior works based on full-wave optimization of the overall structure, this method is fast and leads to accurate bandwidth results. Several filter examples are included to support the design method. A prototype filter has been manufactured and the RF measurements are in good agreement with theory. [ABSTRACT FROM PUBLISHER]

This paper presents a Doherty power amplifier (DPA) based on asymmetric cells using an even input power drive and an appropriate peak fundamental current ratio (FCR) between the peaking amplifier and the carrier amplifier. Using an appropriate output combiner and an even input power drive for the DPA, not only better load modulation but also enhanced power gain can be achieved. After providing an analysis for the fundamental currents, a design guide for the proposed DPA using the peak FCR is presented. For verification, conventional and proposed DPAs were designed using GaN-HEMTs for the 2.14-GHz band. Using a downlink long-term evolution signal having a peak-to-average power ratio of 6.5 dB, comparably better performances were achieved than the conventional DPAs, such as a high power-added efficiency of 55.7% and a power gain of as high as 16.6 dB, at an average output power level of 36.9 dBm. [ABSTRACT FROM PUBLISHER]

In this paper, a novel design method of generalized dual-band unequal filtering power divider (DUFPD) is proposed. Using this method, the power divider (PD) could be designed to realize the dual-band filtering response with arbitrary power division, arbitrary frequency ratio, arbitrary real terminated impedances, independently controllable bandwidth, and excellent isolation. To satisfy these characteristics, a proper dual-band filtering structure is selected to replace the conventional quarter-wave length transmission line in the PD. In addition, a single resistor structure is utilized to obtain effective isolation between the output ports. Furthermore, the complete design procedures and analytical equations of the proposed generalized DUFPD are presented based on the circuit and transmission line theories. To demonstrate the validity of the proposed design method, a DUFPD with different real terminated impedances is designed, fabricated, and measured. We show that there is a good agreement between the simulated and measured results. [ABSTRACT FROM PUBLISHER]

In this paper, we developed three designs of dual-band coupled-line couplers with wide separation between bands. Coupler A was constructed using three cascaded coupled-line sections with a band ratio fH/fL of up to 7. Coupler B, with a stub-tapped coupled line, was developed for compactness and has advantages of high band ratio and controllable bandwidth. Couplers A and B are most suited for weak coupling applications. Coupler C was developed for achieving strong coupling while maintaining a high band ratio, and it was constructed using a coupled-line section connected by two uncoupled lines at its two ends. Coupler C has advantages of high band ratio, strong forward-wave coupling, compact size, and easy fabrication. Coupler A, operating at 0.84 and 5.17 GHz with fH/fL = 6.15 / and a coupling of −10 dB, and Couplers B and C, operating at 0.7 and 2.6 GHz with fH/fL = 3.71 and couplings of −11 and −3 dB, respectively, were fabricated for demonstration. The measured results validate their superior dual-band performance. [ABSTRACT FROM PUBLISHER]

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 two integrated concurrent dual-band class-J power amplifiers (PAs) in AlGaAs–InGaAs pHEMT technology. Design flexibility of class-J space is employed to explore the availability of a dual-band PA where the center frequency of the second band is twice the center frequency of the first band ( f2=2f1 ). The theoretical formulations are developed for f2=2f1 case, for which it is not feasible to obtain high efficiencies using class-F−1, class-F, and other high-efficiency modes. A proof of concept 5/10-GHz class-J PA is manufactured in a 0.1- \mu \textm GaAs pHEMT technology. The proposed PA delivers 26.9- and 26-dBm output power with peak power added efficiencies (PAEs) of 49% and 46% at 5 and 10 GHz, respectively. Another 6/16-GHz ( f2\neq 2f1 ) dual-band concurrent class-J PA with a PAE of more than 50% in both bands is also fabricated in a 0.25- \mu \textm GaAs pHEMT technology. The designed dual-band class-J PA delivers 26- and 25.5-dBm output power at 6 and 16 GHz, respectively. [ABSTRACT FROM PUBLISHER]

This paper reports the first co-design configuration of a power amplifier (PA) in cascade with a high-Q bandpass filter. By matching the filter's input port directly to the transistor's drain node, the conventional output matching network (OMN) of a PA is entirely eliminated. This leads to smaller size/volume, minimized loss, and enhanced overall performance. To enable this co-design method, the matching-filter synthesis theory is proposed and investigated in detail in this paper. Based on this theory, a 3% bandwidth (centered at 3.03 GHz) two-pole filter, implemented using high-Q evanescent-mode cavity resonators, is designed as the PA OMN to provide optimized fundamental and harmonic impedances for a commercial 10-W GaN transistor. Simulation and measured results show that the co-designed PA-filter module yields a desired Chybeshev filter behavior while maintaining excellent PA performance in the passband with 72% efficiency, 10-W output power, >10-dB gain, and 60-dBm output third-order intercept point. This co-designed module experimentally presents a 8% higher overall efficiency compared to a control group developed using a conventional independent PA and filter, which further validates the effectiveness of this method. [ABSTRACT FROM PUBLISHER]

This paper expounds a three-way Doherty power amplifier (3W-DPA) as a solution to the need for high-efficiency wideband power amplifiers when driven by multi-standard signals. The paper begins with a theoretical analysis of 3W-DPA architecture from which the governing equations are derived. This analysis enables the identification of circuit parameters for maximizing bandwidth. A comprehensive methodology was devised to address the practical design challenges resulting from the transistor nonidealities: nonlinear input capacitance, transistor package, and output capacitance. Based on this methodology, a fully analog 30-W 3W-DPA was designed and implemented using GaN packaged transistors. The 3W-DPA prototype maintained an average drain efficiency of 55% at an output back-off of up to 9 dB, over the frequency range of 0.73–0.98 GHz. The 3W-DPA was successfully linearized when driven with 20-MHz four-carrier wideband code division multiple access (WCMDA) signals. 830- and 900-MHz power-added efficiencies of 47% and 53% was achieved at 32- and 35-dBm average output power, corresponding to a peak-to-average power ratio of 11.7 and 7.14 dB, respectively. [ABSTRACT FROM PUBLISHER]

The conventional Doherty power amplifier (DPA) theory is limited to single carrier operations, leading to a nongeneric structure. This paper presents a new analysis that generalizes the conventional DPA (CDPA) theory for increased efficiency and bandwidth. We demonstrate that by introducing a theoretical parameter $\alpha$ at the output combiner, we can redefine the relationships among the output combiner elements for a greater level of design flexibility than it was possible in the CDPA. We also show that previously published works in this area can be considered as special cases of the proposed general theory. As a demonstrator, a specific design, named reduced- $\alpha$ DPA, realized using GaN HEMTs is provided to illustrate the robustness of the approach. This design proves effective for further improving the performance of the previously published 2.14-/2.655-GHz dual-band parallel DPA. A maximum drain efficiency of 84% and 67% at an average of 43-dBm peak and 6-dB back-off power levels, respectively, was measured with continuous wave signals. To quantify the linearity performance, the proposed DPA was tested using wideband CDMA and long-term evolution signals where the adjacent channel leakage ratio was recorded at −25 dBc with an average output power of 38.7 and 36.5 dBm at 2.14 and 2.655 GHz, respectively. [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]

In this paper, a coupled-line balanced-to-single-ended out-of-phase power divider is proposed. Configured by three quarter-wavelength coupled lines, the proposed power divider is compact and able to enhance the bandwidth of differential-mode power dividing, isolation, common-mode suppression, and phase difference between the output ports. Furthermore, enhancing the bandwidth for common-mode suppression using additional quarter-wavelength open stubs is discussed. Analytical solution of the parameters for specified bandwidth can be achieved using odd- and even-mode analysis. Analytical and practical bandwidth limitation has been analyzed, and it is shown that the bandwidths can be controlled by the odd- and even-mode impedance of the coupled lines. For demonstration, a prototype of size 15 mm \times95 mm ( 0.15~\lambda _{g} \times 0.95~\lambda _{g} ) achieves an operating bandwidth ( \vert S_{ddAA}\vert < -20$ dB) of 30% with the minimum insertion loss of 0.1 dB. [ABSTRACT FROM AUTHOR]

This paper presents the design and implementation of a distributed class-J power amplifier (DJPA) in a 0.25- \mu \textm AlGaAs–InGaAs pHEMT technology. Class-J mode of operation is introduced in design of distributed power amplifiers (DPAs) to achieve high power added efficiencies (PAEs) over wide frequency ranges. Extensive load–pull (LP) and source–pull (SP) simulations are performed to show that class-J PAs are less sensitive to proper termination of higher order harmonics, and high PAE and output power can be obtained even if the second, third, fourth, and fifth harmonics comprise a real impedance. This is essential in DPAs as the higher order harmonics of the frequencies at lower side of the band may fall in the desired bandwidth. Based on LP and SP observations, a proof-of-concept 1.5–10-GHz monolithic microwave integrated circuit DJPA is designed and fabricated. Chip dimensions are $2.15\times 2.15$ mm2, and 29–30.7-dBm output power with 33–44% PAE is achieved over the frequency range. The large-signal power gain is greater than 10 dB while the PA maintains an average small-signal gain of 13 dB over the bandwidth. [ABSTRACT FROM AUTHOR]

This paper presents a V -band 1.2-V wideband power amplifier (PA) with a compact four-way radial power combiner in a 90-nm CMOS process. A transformer-based radial power combiner with a 1-dB insertion loss at 60 GHz and a 0.043-mm ^{\mathrm { {2}}} compact size is designed for high-output-power combining and wideband load-pull matching. This PA achieves the saturated output power ( P_{\mathrm { {SAT}}}) of 20.6 dBm, the maximum power-added efficiency ( \textit PAE\mathrm { {max}}) of 20.3%, and a 20.1-dB small-signal gain ( S\mathrm { {21}}) at 60 GHz. The PA maintains a flat 20-dBm P\mathrm { {SAT}} with \textit PAE\mathrm { {max}} better than 17.3% within 50–64 GHz, and it has a 3-dB bandwidth (BW) of 24.5 GHz (41.8–66.3 GHz). The chip area without pads is 0.432 mm ^\mathrm 2 . To the best of the author’s knowledge, this $V$ -band PA with a flat frequency response of 20-dBm P\mathrm { {SAT}} presents the widest large-signal BW (50–64 GHz) compared with the reported 60-GHz CMOS high-output PAs. [ABSTRACT FROM AUTHOR]

This paper presents a general coaxial-conical-coaxial transmission line transition with a built-in impedance taper that can explicitly be chosen or optimized. The presented transition has a smooth profile, which is advantageous for peak power handling, and provides more degrees of freedom and greater flexibility to optimize devices compared with other transitions between conical and coaxial lines or coaxial lines of different sizes. The method is validated by designing and fabricating an eight-way coaxial line combiner, 0.55 $\lambda $ long and $0.26~\lambda $ in diameter, with a measured reflection coefficient of better than −22 dB over a 115% bandwidth (BW), and better than −12 dB over a 130% BW. [ABSTRACT FROM AUTHOR]

In this paper, a thorough design procedure for concurrent design of integrated antiparallel Schottky-diode-based limiter and low noise amplifier (LNA) is presented. The optimum number of limiter branches, the size and number of diodes in each branch, width of the transmission line loaded by diode branches, and design considerations for input transistor of the LNA are discussed in detail. To improve power handling of the limiter with a minimum impact on overall noise figure (NF), a novel limiter structure is proposed where transistors are utilized in a limiter topology. A design procedure is also introduced for the transistor-based limiter-LNA. Developed methodologies are employed to design and fabricate a diode-based and transistor-based limiter-LNA in a 0.1- \mu \textm AlGaAs/InGaAs pHEMT process. Measurement results show that the diode-based limiter-LNA tolerates up to 2-W continuous wave (CW) input power without failure, while transistor-based limiter-LNA is capable of handling 5-W CW input power. Measured average gain and NF for the diode-based limiter-LNA are 21 and 2.3 dB over 28–38-GHz frequency range, while the transistor-based limiter-LNA achieves an average 18-dB small-signal gain and 2.5-dB NF over the 30–38-GHz bandwidth. [ABSTRACT FROM AUTHOR]

A design method for the bandpass filters with even number of resonators is presented for compacter size and wider bandwidth. The design method is based on the conventional filters with two resonators defined as a scattering parameter at a given frequency and a characteristic impedance of a 0^\circ lumped-element equivalent circuit. The filter designed in this paper can be terminated in equal impedances and may have ripple responses at the same time for the wider bandwidths. Since the filter suggested in this paper has advantages that both Butterworth and Chebyshev filters possess, it is called a Butter–Cheby filter to distinguish from conventional filters. For better performance of the Butter–Cheby filter, a way to make transmission zeros is also discussed. To verify the design method, a Butter–Cheby filter with four resonators having 0.01-dB ripple is fabricated with distributed and lumped elements and measured at a design center frequency of 1 GHz. The measured results are in good agreement with the prediction, achieving less than 0.4-dB insertion loss, more than 20-dB return loss, and a transmission zero of 2 GHz. [ABSTRACT FROM PUBLISHER]

In this paper, a simple and effective method is proposed for designing tunable diplexers with constant fractional bandwidth using dual-mode resonators. The proposed method directly connects two independently designed dual-mode bandpass filters and forms a tunable diplexer without any additional matching network at the common port, thus bringing significant design flexibility to the diplexer design process. Also, an alternative design process is proposed to characterize the coupling in the dual-mode resonator and external quality factors at the input/output, making it much easier for constant bandwidth designs. A second- and fourth-order diplexer consisting of dual-mode stepped-impedance microstrip resonators are designed and fabricated to demonstrate this method. The second-order diplexer is tuned using silicon varactor diodes, and covers 1.9–3.4 GHz with an insertion loss of 3.0–5.0 dB. Constant fractional bandwidths of \sim6% and \sim4.5% are obtained for the two frequency channels, respectively. In addition, due to the employment of the stepped-impedance dual-mode resonator, the second-order tunable diplexer occupies a compact area of 0.037\lambda0\times 0.158\lambda0, where \lambda0 is the free-space wavelength at the lowest frequency that the diplexer can be tuned. Simulations and measurements are presented with excellent agreement. Application areas are in multi-standard communication systems. [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]

This paper presents a modified Doherty configuration with extended bandwidth. The narrow band feature of the conventional Doherty amplifier is discussed in the view of the broadband matching. To extend the bandwidth, the post-matching architecture is employed in the proposed design. Meanwhile, broadband low-order impedance inverters are adopted to replace the quarter-wavelength transmission lines. Low-pass filter topologies are used to realize both the post matching network and the impedance inverters. A modified Doherty Power amplifier was designed and fabricated based on commercial GaN HEMT devices to validate the broadband characteristics of this configuration. The 6-dB backoff efficiencies of 47%–57% are obtained from 1.7 to 2.6 GHz (41.9% fractional bandwidth) and the measured maximum output power ranges from 44.9 to 46.3 dBm in the designed band. In particular, more than 40% efficiencies are measured at 10-dB backoff throughout the operation band. [ABSTRACT FROM PUBLISHER]

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

A microwave Doherty power amplifier (DPA) consists of a carrier amplifier (CA), a peaking amplifier (PA), and an impedance inverting network. In this paper, a novel DPA topology with neither the impedance inverting network nor offset lines is proposed. This topology enables the enhancement of amplifier bandwidth and achieves a more compact amplifier size. To remove the impedance inverting network and to realize high efficiency at large back-off power level, the output-matching network of the CA is designed to realize high performance both at a low signal power level in the off-state of the PA and at the saturated signal power level. A 1.9-GHz series-connected load Doherty power amplifier without an impedance inverting network is designed and fabricated using GaN HEMTs. The amplifier achieves a power-added efficiency (PAE) of 50% under a 6-dB output back-off from a 34-dBm saturated output power with a PAE of 59%. A maximum PAE higher than 44% is obtained over a frequency range of 1.63–1.98 GHz. [ABSTRACT FROM AUTHOR]

This paper describes a fully integrated E-band power amplifier (PA) in 40-nm CMOS. The design and layout of the unit PA stage is optimized to achieve high output power while maintaining high power gain. A broadband parallel-series power combiner is proposed to provide the PA stage optimum load impedance across the complete E-band. The complete PA achieves a measured saturated output power of 20.9 dBm with more than 15-GHz small-signal -3-dB bandwidth and 22% power-added efficiency (PAE) at 0.9-V supply. The in-band variation of -1-dB compressed power (P1\ {dB}) is only \pm0.25 dB. This is the first reported silicon-based PA that covers both 71–76- and 81–86-GHz bands with uniform gain, output power, and PAE. [ABSTRACT FROM AUTHOR]

This paper presents a wideband vector-sum phase shifter (VSPS) that operates over the entire WR-3 band (220–320 GHz). Compared to conventional VSPSs with double Gilbert cells, the proposed phase shifter employs a single Gilbert-cell structure for vector modulation. This reduces the output current combining ratio from 8:2 to 4:2, and boosts the impedance at the combining node, thus facilitating wideband output matching at upper millimeter-wave and terahertz bands. The simplified structure leads to a reduction in dc power consumption and chip area without sacrificing the 360^\circ phase-shifting property. Lossy matching is applied at the Gilbert-cell output to further increase bandwidth and stability at the expense of relatively high loss. The phase shifter is implemented using a 250-nm InP DHBT technology that provides f T and f \max exceeding 370 and 650 GHz, respectively. The measurements exhibit a wideband phase shift with continuous 360^\circ coverage and average insertion loss ranging from 11.8 to 15.6 dB for the entire WR-3 band. The root mean square amplitude and phase error among different phase states are less than 1.2 dB and 10.2^\circ, respectively. The input-referred 1-dB compression is measured at \0.7 dBm on average. The dc power consumption is 21.8–42.0 mW at different phase states. [ABSTRACT FROM PUBLISHER]

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]