Search

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

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]

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

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

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

In this paper, a guided-wave structure, the half-mode composite waveguide (HMCW) is proposed and presented. Similar to the conventional mode composite wave- guide (MCW), the HMCW also has an inner and outer waveguides, each working in its half-mode operation, respectively. In the HMCW structure, the signal propagates in the inner waveguide with quasi- $\text{TE}_{0.5-0}$ mode and along the outer waveguide with the quasi-TEM mode. The HMCW’s half-mode operation principle, impedance, loss, and propagation characteristics including higher order modes are analyzed. Compared to its full-size counterpart, the HMCW only occupies half the space, when operating within the same frequency band. Simulation results show that the transmission loss of the HMCW is comparable to that of the full-size MCW. Thus, it is also suitable for both low- and high-frequency design and applications. To measure and integrate the HMCW with other planar circuits, a joint feeding network for the HMCW is also proposed. Its circuit prototype is fabricated on three layers of substrate using a multilayer substrate integration technique. This joint feeding network can simultaneously excite the inner and outer waveguides, respectively, in an independent manner. In measurements, both the inner and outer waveguides are transitioned to microtrip lines, and a good matching is achieved from 4.4 to 11.2 GHz with a relative bandwidth of 87.2% for the outer waveguide at low frequency and from 18.6 to 32.6 GHz with a relative bandwidth of 54.7% for the inner waveguide at high frequency, respectively. [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 presents a method to obtain the characteristic impedance ( Z\text {C} ) and the complex permittivity ( \hat \varepsilon ) of single-ended and edge-coupled interconnects on printed circuit board (PCB) technology. For this purpose, experimentally determined propagation constant ( $\gamma $ ) data are used in combination with the frequency-dependent resistance ( $R$ ) and inductance ( $L$ ). Due to the difficulty of directly obtaining $R$ and $L$ from measurements, closed-form equations are used to perform the corresponding calculation. In this regard, the current distribution effects are considered within the cross section of the signal traces and the ground plane. The proposal was validated for both, single-ended and edge-coupled PCB interconnects considering three cases: standard, medium-loss, and in low-loss materials. The results show that the extracted data are in agreement with values reported in material datasheets at 4 GHz. In this regard, the method is a good alternative to characterize planar transmission lines on PCB technology within the whole frequency range where the S-parameter measurements are performed. [ABSTRACT FROM AUTHOR]

Non-Foster elements are highly desired to overcome the bandwidth limit of electrically small antennas, cloaking, and metamaterials. However, they are prone to be unstable and thus it is quite challenging to implement non-Foster circuits in practice. Hence a rigorous and effective method of analyzing the stability should always be the priority when designing a non-Foster network. This paper applies normalized determinant function to analyze the stability of non-Foster circuits. A floating-version negative capacitor based on Linvill’s negative impedance converter is taken as the example. Factors affecting the stability in the practical design are thoroughly investigated, including device parasitics, dc biasing, distributed transmission line in the layout and load impedance. Circuit parameters are substituted with practical values to reduce the complexity of calculation. Finally, experiments are conducted to verify the analysis. [ABSTRACT FROM AUTHOR]

This paper investigates L-shaped iris (LSI) embedded in substrate integrated waveguide (SIW) structures. A lumped element equivalent circuit is utilized to thoroughly discuss the iris behavior in a wide frequency band. This structure has one more degree of freedom and design parameter compared with the conventional iris structures; therefore, it enables design flexibility with enhanced performance. The LSI is utilized to realize a two-pole evanescent-mode filter with an enhanced stopband and a dual-band filter combining evanescent and ordinary modes excitation. Moreover, a prescribed filtering function is demonstrated using the lumped element analysis not only including evanescent-mode pole, but also close-in transmission zero. The proposed LSI promises to substitute the conventional posts in (SIW) filter design. [ABSTRACT FROM PUBLISHER]

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

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

This paper 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]

This paper presents a novel class of multilayered ultra-broadband bandpass filters based on high-impedance slotline resonators. The equivalent circuit and electrical properties of the proposed high-impedance slotline resonator realized on a low-permittivity substrate are first discussed. To largely remove the radiation losses of the devised high-impedance slotline resonator, two identical shunt-connected folded low-impedance slotline sections are utilized to replace one short-circuited high-impedance slotline section. Through the synthesis design of an ultra-broadband microstrip-to-microstrip vertical transition, the effective impedance of the conceived shunt-connected low-impedance slotline sections is confirmed and the impedance variations of this proposed high-impedance slotline resonator are quantitatively determined by the means of the extracted turns ratios of the employed transformers. To further demonstrate the effectiveness of the engineered slotline resonator in terms of radiation reduction and verify its equivalent circuit model, a new type of multilayered high-order bandpass filters with ultra-broadband Chebyshev equiripple filtering response is theoretically presented. Furthermore, for experimental validation purposes, a 2-GHz two-layered bandpass filter prototype is fabricated and measured. It exhibits a seven-pole ultra-broadband filtering response, high in-band amplitude/group-delay flatness, highly reduced radiation losses, and sharp-rejection upper-stopband characteristics. [ABSTRACT FROM AUTHOR]

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

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

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

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

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

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

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

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]

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]

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

With rapidly increasing switching speeds and surge current requirements, placement of local decoupling capacitors is becoming critically important in high-speed low-power designs. In this paper, utilizing the driving-point impedance (viewed from the device pin) as a metric, a new method is presented for the placement of decoupling capacitors in parallel-plate power ground pairs of high-speed circuits. In the proposed approach, instead of using the traditional trial-and-error method to identify an appropriate placement distance, the process is formulated in the form of a transcendental function. The resulting function is solved using Newton–Raphson (N-R) iterations to give a direct solution for the distance. Also, an analytical representation based on Hankel functions for the driving point impedance and its derivatives is developed to speed up the N-R iterations. The proposed method is validated by comparing the results with the full-wave electromagnetic simulations. [ABSTRACT FROM PUBLISHER]

In this paper, a model for the input impedance of a hot-wire electro-explosive device (EED) based on differential-mode measurements is proposed. The model represents the EED using three transmission line segments in cascade. The characteristics of each segment are estimated according to data reported in the literature and to measurements of the differential-mode input impedance of actual EEDs in the ultrahigh frequency range. The experimental procedure and model are presented in detail. In addition, the impedance measurements and the predictions of the proposed model are compared with previous results reported in the literature. [ABSTRACT FROM PUBLISHER]

This paper presents a compact and wideband millimeter-wave antenna-coupled detector, with a Schottky diode directly integrated across the feeding terminals of a planar dipole. An integrated wideband dipole is proposed, as a radiator as well as a radio frequency choke. It contains a pair of folded strips for broadening the bandwidth and a pair of U-slot resonators for sidelobe reduction, both of which facilitate the compact design. To form unidirectional radiation with a low profile, a hybrid reactive impedance surface is presented, which can simultaneously enhance the gain and impedance bandwidths covering the full Ka-band. An equivalent circuit model is provided to illustrate the operating mechanism of this antenna-coupled detector, and the mounting effect caused by the diode is examined. A Ka-band prototype with dimensions of about 1.12\lambda 0\times 1.12\lambda 0\times 0.08\lambda 0 is fabricated and characterized, exhibiting a responsivity between 1500 and 3800 V/W over the full Ka-band. The proposed design has the advantages of broad bandwidth, low profile, small footprint, and mechanically stable structure. It can be fabricated using low-cost printed circuit technology, and can easily be configured into a planar 2-D array, making it suitable for low-cost sensing and imaging applications based on small unmanned aerial vehicles. [ABSTRACT FROM PUBLISHER]

Modulation of load impedance is an effective way to maintain efficient power amplifier (PA) operation over high dynamic range modulated signals. For high efficiency, a load modulation approach can be applied to inherently efficient classes of PAs such as those with harmonic tuning: Class J, Class F, and Inverse Class F. This paper presents an analysis of harmonically tuned (HT) amplifiers operating under load modulation conditions, deriving the optimal loading trajectories for these multiple classes of operation. Because these load trajectories are complex, it is then shown—through a series of analysis, simulations, and measurements—that HT amplifiers are better suited for outphasing systems, than conventional amplifiers such as Class B. A design methodology is proposed and validated through design and measurement of a 900-MHz outphasing system, comprising of two Gallium Nitride Class J branch PAs, delivering 44.6 dBm with 75% PAE at saturation, while mantaining PAE above 60% over a 7-dB output power back-off. [ABSTRACT FROM PUBLISHER]

This paper introduces a transformer-based, dual-coupled, triple-mode voltage-controlled oscillator (VCO) using a transformer-based fourth-order tank with tunable transconductance feedback between the primary and secondary coils. The tank impedance can be reshaped by the transconductors through the tuning of their biasing currents. By controlling the bias currents, the VCO has three different operational modes, capable of generating a single frequency in either the 3- or 5-GHz band as well as two frequencies in the 3- and 5-GHz bands simultaneously. The measured phase noise at 1-MHz offset frequency is -109.5 and -118.8 dBc/Hz when the oscillator oscillates at a single frequency of 5.24 or 3.22 GHz, respectively. The phase noise is -104.3 and -112.6 dBc/Hz, respectively, when the oscillator oscillates at 5.34 and 3.03 GHz simultaneously. The triple-mode VCO was fabricated in a 0.13-\mum CMOS process, occupies a core area of 0.16 mm^2, and dissipates 5.6 mW from a 1.2-V supply. [ABSTRACT FROM AUTHOR]

This paper presents a frequency-sweep technique based on model-order reduction and finite elements, for the broadband analysis of structures fed by waveguides (WGs) possessing frequency-dependent modal field patterns. Standard order reduction requires the matrices and right-hand sides (RHSs) to exhibit affine frequency parameterization. This precondition is violated when the transverse fields of the WG modes vary with frequency. The proposed solution involves two steps. First, a reduced-order model (ROM) for the WG is constructed. It enables the accurate yet inexpensive computation of propagation characteristics. Second, order reduction is applied to the driven problem, wherein the reduced WG model is utilized to construct affine approximations to the matrices and RHSs. Since this process requires operations on reduced-order matrices only, it is computationally cheap and enables offline/online decomposition. Both impedance and scattering formulations are considered. For the latter, an alternative to the transfinite element method is proposed, which does not employ modal field patterns as shape functions. It avoids interior resonances and computes scattering parameters more efficiently when only a limited set of excitations is of interest. The resulting algebraic system is of somewhat larger dimension but easier to assemble. Its simple structure greatly facilitates the construction of the ROM. [ABSTRACT FROM PUBLISHER]

A compact quad-band bandpass filter using quad-mode stepped impedance resonator (QMSIR) is investigated in this paper. To get suitable coupling within the four passbands, the multiple coupling circuits between the input/output ports and QMSIR are applied. Based on the symmetry of the QMSIR, even- and odd-mode theory is used to analyze the equivalent circuits of the QMSIR. Design equations are derived, and they are used to guide the design of the circuits. Four passbands can be easily tuned by its physical dimensions. Upper stopband is improved by adding the open-loop SIRs at both I/O ports. Transmission zeros among each passbands are generated, resulting in high isolation and frequency selectivity. An experimental circuit is fabricated and evaluated to validate the design concept. The measurement results are in good agreement with the full-wave simulation results. [ABSTRACT FROM PUBLISHER]

This paper presents the design and comparison of three $K$ -band sensing oscillators in the standard 0.25- \mu \text{m} SiGe:C BiCMOS technology featuring an open stub, a shunt stub, and a combination of both. The different stub types are combined with the capacitive and/or inductive elements of the particular oscillator and serve as the sensing elements in the respective setup. The input impedances of the stubs depend on the permittivity of the medium. Therefore, the oscillation frequencies and the output power correspond to the dielectric material under test (MUT). The sensor response to different dielectric properties has been investigated using different compositions of methanol-ethanol solutions. In the conducted experiments, the proposed architectures show a maximum frequency shift of 5% (27.8–26.4 GHz) for a change in permittivity of 2.4 (4.1–6.5) of the MUT. Each of three sensors has a chip area of 0.6 mm2 and consumes less than a 12-mW power. The proposed sensor is a potential component for future low-power frontends to perform minimally invasive investigations of biomaterials. [ABSTRACT FROM PUBLISHER]

This paper addresses design and implementation of integrated rectifier-antennas (rectennas) for wireless powering at low incident power densities, from 25 to 200 \mu\W/cm^2. Source–pull nonlinear measurement of the rectifying devices is compared to harmonic-balance simulations. Optimal diode RF and dc impedances for most efficient rectification, as a function of input power, are obtained. This allows optimized antenna design, which can eliminate or simplify matching networks and improve overall efficiency. As an example of the design methodology, Schottky diodes were characterized at 1.96 GHz and an antenna is matched to the optimal complex impedance for the most efficient rectifier. For incident power density range of interest, the optimal impedance is 137+ j149\ \Omega, with an RF to dc conversion efficiency of the rectifying circuit alone of 63% and total rectenna efficiency of 54%. [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]

This paper presents an analysis of ideal power amplifier (PA) efficiency maximization subject to a finite set of arbitrary complex harmonic terminations, extending previous results where only purely reactive harmonic terminations were treated. Maximum efficiency and corresponding fundamental output power and load impedance are analyzed as a function of harmonic termination(s). For a PA restricted to second harmonic drain waveform shaping, maximum efficiency as a function of second harmonic termination is treated for cases of both purely real and complex fundamental frequency impedances. For the case of a PA restricted to second and third harmonic drain waveform shaping, peak efficiency as a function of third harmonic impedance with an ideal second harmonic termination is analyzed. Additionally, the sensitivity of PA efficiency with respect to the magnitude and phase of the second and third harmonic load reflection coefficients is examined. The analysis is extended to include device and package parasitics. The paper concludes with a discussion of how the presented general analysis method provides useful insights to the PA designer. [ABSTRACT FROM AUTHOR]

Approximate analytical formulae are presented for calculating the characteristic impedance of elevated coplanar waveguides (CPWs). In such a structure, both the signal and ground traces are suspended above a substrate using airbridge technology. The analysis of this structure is formulated in terms of partial capacitances obtained through conformal mapping techniques. The paper highlights the limitations of previously published formulae. Furthermore, the paper presents a method to overcome these limitations over a limited range of practical geometries. Comparisons between measured, simulated, and calculated results are included, and excellent agreement is obtained for a wide range of geometries. In addition, the effects of CPW-to-elevated coplanar waveguide transitions and supporting posts on the characteristics of elevated lines are analyzed. Good agreement is obtained for a relatively complex fabricated structure which is nonuniform at nine points in the direction of signal propagation. The fabrication of elevated CPW structures is also discussed. [ABSTRACT FROM AUTHOR]

In this paper, a synthesis method by applying the Taylor series is proposed to design a variety of low-pass mixed lumped and distributed circuit networks, including the low-pass filters and low-passing impedance transformers. First, the principle of applying the Taylor polynomials for these mixed circuit networks is discussed. Herein, the trigonometric functions, commonly used to characterize distributed circuits, are expressed in the form of polynomials by the application of Taylor polynomials. Therefore, the transfer function of the mixed networks is simplified from a multivariable to a polynomial form. Following this, a generic circuit structure is proposed to design either a low-pass filter or a low-passing impedance transformer with specified port impedances. The desired filtering function uses the similar method to transform the trigonometric function into a format of polynomials. Under the equalization of the transfer function and filtering function, all the unknown design parameters are obtained. As two examples, a low-pass filter and a low-passing impedance transformer are synthesized, designed, and fabricated to experimentally verify the proposed design approach. [ABSTRACT FROM PUBLISHER]

In this paper, we systematically investigate the electromagnetic (EM) field of a stripline dipole coil element backed by various shielding plates, which are characterized by surface impedance. The initial analysis is based on a 2-D finite-element-method model, where the considered surface impedance was categorized in terms of magnitude and phase. It has been demonstrated that the shielding plate can be approximately modeled by the magnitude of a complex surface impedance if the absolute EM field distribution is considered. Additionally, as the magnitude of the surface impedance increases, the magnetic and electric fields excited by the stripline tend to distribute in a broader manner. Thus, the transversal homogeneity of the B1 field of a stripline coil can be improved by a shielding plate with a high surface impedance, which has been verified by 3-D models based on single- and multi-coil elements. For the experimental validation, two shielding plates—a copper-plated substrate and a high-impedance surface, which exhibits a small and large surface impedance, respectively—are considered. An excellent agreement of field distributions between numerical simulation and measurement has been observed. [ABSTRACT FROM PUBLISHER]

A primary factor affecting optimum performance of microwave multipliers employing nonlinear devices is the proper termination of the fundamental and other harmonic frequency components. The objective of this paper is to present a quantitative analysis leading to the assessment of optimum terminating impedances in the design of active frequency multipliers with special attention given to harmonics other than those desired. The analysis includes computer modeled HEMT data and supporting measured data for corresponding circuit realizations. Circuit designs are presented utilizing HEMT transistors as the active element to verify modeled results. Based on available literature, the results demonstrate, for the first time, the quantitative effects of harmonic termination on active multiplier conversion gain and fundamental and higher harmonic suppression. An experimental design reveals an improvement in multiplier gain of 124% over the conventional approach and data is presented which quantitatively illustrates the advantages of impedance termination considerations under optimal bias conditions. [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]

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]

A reactance-compensation technique has been introduced recently for the design of wideband class-E power amplifiers (PAs). With this technique, the load resistance can be transformed to an optimal complex drain impedance in a broad frequency band. One potential problem of this technique is that an additional network is often needed to transform 50 \Omega to the optimum load resistance, which is typically at a lower value. This paper proposes a method to improve the reactance compensation technique. By using the proposed method, the required low-value load resistance is up to four times the original value. This is achieved not by adding more components, but by simply changing the order and values of them. With the proposed method, the additional resistance matching network is no longer needed in many cases, or can be significantly simplified in other cases. To validate the theory, two broadband class-E amplifiers were designed using the original technique and the proposed method, respectively. The performances of the two amplifiers are compared. By using similar complexity of matching networks, the PA designed using the original method can achieve better than 70% power-added efficiency for a fractional bandwidth of 42%. The PA designed using the proposed method can achieve above 70% efficiency for a bandwidth of 51%. The proposed method can be used in the design of many other types of amplifiers. [ABSTRACT FROM PUBLISHER]

A tunable highly integrated bandpass–bandstop filter (BSF) cascade that is capable of dynamically relocating its transmission zeros arbitrarily close to its passband without causing parasitic resonances and additional mismatch loss is demonstrated in this paper. An arbitrary phase BSF that enables a compact cascade topology and an extension of the classical coupling matrix synthesis for filters terminated with a complex impedance are the key advantages of the proposed bandpass–BSF cascade. Independent and simultaneous tuning of the passband center frequency, bandwidth, and transmission zeros are possible in this topology. The proposed cascade synthesis approach is experimentally validated using commercially available lumped elements. In these implementations the transmission zeros can be placed on the skirt of the bandpass filter and can be used to create high isolation (50-dB notch 4.7% away from the passband edge), increase the selectivity of the passband, and tune the fractional bandwidth from 3% to 9% without additional mismatch loss. [ABSTRACT FROM AUTHOR]

This paper extends the conventional coupling matrix theory for passive filters to the design of “filter-amplifiers,” which have both filtering and amplification functionality. For this approach, extra elements are added to the standard coupling matrix to represent the transistor. Based on the specification of the filter and small-signal parameters of the transistor, the active $N + 3$ coupling matrix for the “filter-amplifier” can be synthesized. Adopting the active coupling matrix, the last resonator of the filter (adjacent to the transistor) and the coupling between them are modified mathematically to provide a Chebyshev response with amplification. Although the transistor has a complex impedance, it can be matched to the filter input by the choice of the coupling structure and the resonator frequency. This is particularly useful as the filter resonators can be of a different construction (e.g., waveguide) to the amplifier (e.g., microstrip). Here, an X-band filter-amplifier is implemented as an example, but the technique is general. [ABSTRACT FROM AUTHOR]

This paper presents a novel method for designing Gysel power dividers with arbitrary power-division ratios as well as filtering responses. A coupling structure is utilized to replace the quarter-wavelength microstrip line in the power divider. By altering the coupling strength, the power ratio can be arbitrarily controlled with the highest ratio of 10:1. Furthermore, the coupling structures enable the filtering function of the power divider. Two transmission zeros are created near the passband edges, resulting in high-selectivity quasi-elliptic responses. Theoretical analysis is carried out, and closed-form equations are derived based on circuit theory and transmission line theory. For demonstration, three filtering Gysel power dividers are implemented with different power-division ratios (1:1, 3:1, and 10:1). In all of these circuits, power splitting and bandpass filtering functions are observed with good performance. Comparisons of the measured and simulated results are presented to verify the theoretical predications. [ABSTRACT FROM AUTHOR]

This paper presents the design of concurrent multiband Doherty power amplifiers (MB-DPA) based on a newly developed multiband impedance inverter network (MB-IIN). The design concept can theoretically be applied to a large number of frequency bands. To support the design of MB-DPAs, a detailed realization of the MB-IIN is introduced for the first time. For verifying the proposed MB-IIN design technique, tri-band and quad-band DPAs for 950, 1500, 2140, and 2650 MHz are designed, implemented, and characterized. Measurement results show good performance in terms of efficiency, linearity, and especially the pronounced Doherty behavior in all targeted bands, demonstrating the prospective applications of the developed MB-IIN in the design of concurrent multiband Doherty power amplifiers for wireless communications. [ABSTRACT FROM AUTHOR]

A microwave three-channel selector, showing twofold symmetry using tri-operational mode synthesized transmission lines, is proposed and investigated in this paper. On one hand, just like a typical triplexer, the three-channel selector provides independent transmission paths at three different frequencies; however, on the other hand, the twofold symmetry makes each of the ports able to serve as the common input. The arrangement of the proposed channel selector is unique and can be applied to synthesize a tri-mode heterogeneous integrated beam-switching/Van Atta/phase-conjugating array. The operational principle is introduced first, followed by the details of the synthesized lines as the core building blocks; design formulas are discussed along with the results. Experimental validation verifies the design concept, and discussions on its potential applications are provided. [ABSTRACT FROM AUTHOR]

In this paper, the line-offset offset-open offset-short (LZZ) calibration technique for vector network analyzers (VNA) is introduced. The LZZ uses as calibration standards a fully known transmission line and two offset reflecting loads. The mathematical formulation of the LZZ is based on the use of ABCD-parameters for modeling the imperfect VNA as well as calibration standards. As a result, it is shown that the error coefficients characterizing the imperfect VNA can be calculated by comparing the estimated impedance of the two loads with the characteristic impedance of the transmission line. In order to validate the proposed method, the line–reflect–line (LRL) and the line–reflect–reflect–match (LRRM) calibration techniques are used. A high correlation between the S-parameters of a heterostructure field-effect transistor corrected with the LRL, LRRM, and LZZ techniques up to 45 GHz is achieved. [ABSTRACT FROM PUBLISHER]

The evolution of the mobile handset in support of fourth-generation and beyond technology requirements continues to introduce significant challenges. Tunable systems promise improvements in performance and flexibility with the significant potential to relax limitations currently imposed on traditional RF components and systems. This paper introduces novel techniques based on tunable systems that enable the handset to learn the complex impedance at any stage of its RF front-end in real-time. The proposed approaches are based on utilizing readily available information from the receiver or can be easily obtained with simple perturbations of the system. The added flexibility of this previously unavailable information enables the implementation of new smart handset applications including improved handset performance. The methods are presented through simulations and measurements. [ABSTRACT FROM PUBLISHER]

This paper presents a novel high performance ultra-wideband (UWB) bandpass filter that satisfies FCC UWB specifications. The filter is based on a composite right/left handed (CRLH) structure consisting of an asymmetric unit-cell with a short circuited inductive stub that exhibits stopband rejection level greater than 25 dB at both the lower and upper band edges while maintaining an insertion-loss of less than 0.5 dB across its passband. In addition, a simple and effective technique is proposed to create and control sharp rejection notch-bands within the filter's passband in order to provide interference immunity from undesired radio signals, such as wireless local area networks (WLAN) that co-exist within the UWB spectrum. The proposed technique was verified practically to validate the design methodology. The experimental results of the prototype circuit are presented and compared with the simulation results. The dimensions of the proposed filter are 0.37\lambda\times 0.10\lambda (i.e., 16.4\times 4.8\ mm^2). The filter's characteristics and compact size make it suitable for UWB systems. [ABSTRACT FROM AUTHOR]