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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 proposes a design scheme of concurrent dual-band Doherty power amplifier (DPA) which can be reconfigured to two different pairs of concurrent dual bands for multiband and carrier aggregation applications. In addition to the reconfiguration of frequencies of operation, the output power back-off (OPBO) region for efficiency enhancement can also be reconfigured in this DPA. As a proof of concept, a reconfigurable and concurrent dual-band DPA is designed to operate at 1500 and 2140 MHz in the first concurrent dual band, whereas on reconfiguration it will operate concurrently at 1850 and 2350 MHz. While operating in the first concurrent dual band, the DPA has an enhanced efficiency region up to 6-dB OPBO level and, after reconfiguration to the second concurrent dual band, this region extend up to 9-dB OPBO level. The proposed DPA is tested using continuous wave (CW) signals in single mode as well as in concurrent mode. Measurement results using CWsignals in single mode reveal a drain efficiency of 52%–56% at 6-dB OPBO in the first concurrent dual band. Similarly, in the second concurrent dual band, a drain efficiency of 43%–48% is achieved at around 9-dB OPBO. The peak drain efficiency at saturation is better than 60% in all the four operating bands. The measured aggregated drain efficiencies are 49% and 44% in the first and second concurrent dual bands for 6 and 9 dB OPBO level, respectively. The measured carrier to the third-order intermodulation distortion is better than 17 dBc for all of the operating bands. [ABSTRACT FROM PUBLISHER]

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]

This paper proposes a simple and effective method to designing wide-stopband bandpass filters and diplexers using uniform impedance resonators. Microstrip terminated parallel coupled lines are utilized to generate the filtering functions. By adjustment of the electrical lengths of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be obtained. Appropriate positioning of these zeros enables the suppression of spurious frequencies. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for both homogeneous and inhomogeneous mediums are given in detail. Different combinations of the frequency position of the transmission zeros can provide various characteristics. To extend the stopband bandwidth, one or more transmission zeros can be distributed on different harmonic frequencies. To demonstrate the proposed method, two bandpass filters and a diplexer are designed and fabricated. The measured results are in good agreement with the simulated ones. The first filter provides a high attenuation of 40 dB up to 6.8 times the fundamental frequency $(f_{{{0}}})$ and the second filter provides a lower attenuation of 28 dB, but this time extending up to $14.9f_{{{0}}}$ . [ABSTRACT FROM AUTHOR]

This paper introduces models of the time-domain echoes generated by faults in transmission lines excited by test signals, e.g., as in applications of time-domain reflectometry (TDR). Faults considered here include local modifications of the propagation characteristics of a transmission line. It is shown that the responses of faults are strongly dispersive in nature, which implies that the peak of their echo is far from providing an accurate measure of the severity of the fault, as it heavily depends on the frequency content of the test signal as well as on the length of the fault. It is argued that fault detection in transmission lines is an ill-posed problem that requires a priori knowledge on the fault itself. These results are important for applications of TDR methods, particularly for early warning monitoring of potentially critical faults from their onset, since it is shown that echoes from faults tested at relatively low frequencies can lead to underestimate their actual severity. [ABSTRACT FROM PUBLISHER]

In this paper, a new class of wideband phase shifters on multimode resonator is proposed and developed. Compared with its conventional counterparts, these new phase shifters have a few advantageous features such as simple structure, intrinsic wideband characteristic, large phase-shift value, and easy adjustment in phase shift. The phase properties of multimode resonator are at first studied to derive the quantitative relationship between the phase slope and their respective resonant frequencies. On the one hand, a prescribed wideband phase shift can be achieved by adjusting the impedance ratio Rz of the multimode resonator and the electrical length of the reference line. On the other hand, the wide operating band can be intrinsically obtained over a frequency range covered by multiple resonant frequencies in the multimode resonator. In this context, the transmission-line models of the proposed phase shifters are deduced and synthesized to design these phase shifters with a prescribed phase shift value and return loss within the operating band. Moreover, the synthesized model can be directly mapped into all the physical dimensions, thus allowing for a quick design process. Finally, two 180° wideband phase shifters are designed, fabricated, and tested to verify the proposed design method and predicted frequency responses. [ABSTRACT FROM PUBLISHER]

In this paper, an efficient free-positioning wireless power transfer (WPT) system for charging multiple devices is proposed. For the system, a planar transmitting (Tx) coil that consists of a spiral coil and concentric multiple parallel loops and switchable impedance matching networks (IMNs) at a transmitter are developed. Using the Tx coil, mutual inductance between the Tx coil and the receiving (Rx) spiral coils is made uniform in the effective charging area. The parallel loops are placed in the interior of the Tx coil, and the magnetic field is enhanced and controlled by adjusting the space in each parallel loop. For optimal design of the coil, an analysis method using an equivalent circuit is explained in detail. It is found that the current of one loop of a parallel loop is more than the input current and negative current flows on the other loop, while the total current of each parallel loop is constant. An array of parallel capacitors with a switch as the switchable IMN is used for the maximum power transfer efficiency corresponding to the number of devices. The reflection coefficients of the fabricated WPT system are under −10 dB at 6.78 MHz, regardless of the number of devices and positions. The WPT system has the maximum power transfer efficiencies of 93% for two devices and simultaneously transfers uniform power to up to four devices with high efficiency. [ABSTRACT FROM PUBLISHER]

This paper presents the design and thorough on-wafer characterization of two G-band low-noise amplifiers (LNAs) implemented using 0.13- \mu \textm silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) with peak fT/f\max of 300/500 GHz. The impact of the substrate network and optimized via interconnections on the SiGe HBT performance is investigated to ensure that maximum performance is extracted from each SiGe HBT. The two LNAs are separately implemented using only cascode pairs and only common-emitter (CE) SiGe HBTs to determine which configuration yields better performance in a multistage G-band LNA. The cascode LNA achieves a peak gain of 24.0 dB at 158 GHz with a mean noise figure (NF) of 8.2 dB from 145 to 165 GHz, while the CE LNA achieves a 17.2 dB of gain at 183 GHz with a mean NF of 8.0 dB across 165–200 GHz. A novel implementation of blackbody noise sources for on-wafer Y-factor NF measurements reduces the waveguide length needed to transition between the antenna and the probe, which significantly reduces the sensitivity to jitter. To the authors’ knowledge, these LNAs achieve the lowest reported NF of all SiGe LNAs at these frequencies to date, and the results demonstrate that SiGe HBTs are viable options for millimeter-wave performance-constrained applications. [ABSTRACT FROM PUBLISHER]

In the last decades, several analytical approaches for linear RF modeling and design have been introduced. In general, using these approaches, source and load reflection coefficients are calculated for designing input and output matching networks. This reflection coefficient is set to achieve a specific target such as maximum output power and minimum noise or an intermediate condition. The most common linear design approach is the use of S-parameters. However, S-parameters cannot model the nonlinear behavior of amplifiers. Nonlinear RF systems such as power amplifiers are typically designed using nonlinear models and/or load-pull measurements. Recently, X-parameters have been presented to model nonlinear device behavior. In this paper, a new design approach based on X-parameters has been introduced and will be verified by simulations and experimental results. Also, it will be indicated that this method speeds up the design procedure when compared with the load-pull method. Using this approach, we can calculate the load reflection coefficient at the fundamental frequency for minimizing a specific harmonic output power. Finally, the application of this approach in minimizing a specific harmonic in the output signal and increasing the dynamic range of the amplifier will be investigated. [ABSTRACT FROM PUBLISHER]

A methodology of using five discrete mushroom-like loadings to reduce the mutual coupling of a closely spaced four-element multiple-input multiple-output antenna system is presented in this paper. The occurrence of the loadings concentrates part of the near fields of the substrate integrated cavity-backed slot (SICBS) antenna element and changes the near-field distribution between each antenna elements, so that the mutual coupling between the antenna elements can be greatly reduced. The loaded four-element SICBS antenna system with an overall size of 1.2\lambda 0 \times 1.2\lambda 0 \times 0.11\lambda 0 ( \lambda 0 is the free-space wavelength at the 2.4 GHz) realizes the mutual coupling reduction of 14 dB between the antenna elements along the diagonal lines with identical polarization, while keeping the mutual coupling of the orthogonally placed adjacent elements unchanged over the band of 2.4–2.485 GHz. With the mutual coupling lower than −35 dB between each antenna element pair, the envelope correlation coefficient is less than 0.005 across the operating bandwidth of 2.4–2.485 GHz. [ABSTRACT FROM PUBLISHER]

In this paper, a network approach for the analysis of a wireless resonant energy link consisting of $N$ inductively coupled $LC$ resonators is proposed. By using an artificial transmission line approach, the wireless link is modeled as a transmission line described by effective parameters. It is shown that the analyzed system exhibits a passband filter behavior. More specifically, the reported results demonstrate that in the wireless link passband the effective parameters assume negative values resulting in a negative phase delay. Useful design formulas are derived and validated by comparisons with the experimental data. [ABSTRACT FROM PUBLISHER]

This paper proposes a broadband coplanar waveguide (CPW)-to-rectangular waveguide (RWG) transition using stub resonators. The reflection coefficient of the proposed transition is less than −20 dB in the frequency band ranging from 8.6 to 12.6 GHz, which almost covers the whole X-band (8.2–12.4 GHz). As compared with the miniaturized CPW-to-RWG transition using the inductance-compensated slotline, the reflection coefficient is reduced from −15 to −20 dB and the size is maintained at 8.6 mm. In order to reduce the circuit size, a compact CPW-to-RWG transition using right-angled stub resonators is proposed. The circuit size is reduced from 8.6 to 7.8 mm while the broadband response of the −20-dB reflection coefficient is maintained. In order to verify the simulation results, three back-to-back CPW-to-RWG transitions are fabricated and measured by which the measurement results agree with the simulation results. [ABSTRACT FROM PUBLISHER]

\epsilon -near-zero (ENZ), \mu -near-zero (MNZ), and \epsilon -and- \mu . The wave impedance Z=({\mu /{\epsilon }})^{1/2} , though, is different for the different materials. For the EMNZ, the impedance can remain finite, in contrast to the ENZ and MNZ materials. Therefore, the electric and magnetic fields within the EMNZ can remain coupled, unlike the ENZ and MNZ. This paper presents an analysis of dispersivity in an EMNZ layer under the condition of balance \mu _{r}=\epsilon _{r}$ . One possible application for this condition is seen in the analysis of transmission and reflection from an EMNZ–free space interface, which reveals that a perfect match condition is possible for normal incidence, while for any other incidence angle, this interface is a perfect reflector. [ABSTRACT FROM PUBLISHER]

The design strategies and the implementation of a two-stage concurrent dual-band (DB) microwave harmonic-tuned power amplifier (PA) are presented in this paper. The power stage and the driver stage of this circuit are designed to operate under DB class-F conditions and DB inverse class-F conditions, respectively. The proposed DB harmonic control network of the power stage is implemented by combining a composite right/left-handed transmission line and a DB biasing line with harmonic tuning. A novel DB interstage matching network is developed to transfer the optimum fundamental output impedances of the driver stage to optimum fundamental input impedances of the power stage, as well as suppress the third harmonics at two frequency bands of interest. In the nonconcurrent mode (CM), the measured output power of the two-stage DB PA achieves two peaks of 40.2 and 40 dBm at 1.62 and 2.08 GHz with the maximum power-added efficiencies (PAEs) of 71.5% and 73%, respectively. In the CM, the maximum average PAE is up to 62%. To our best knowledge, the implementation of the two-stage concurrent DB harmonic-tuned PA is reported for the first time in the literature. [ABSTRACT FROM PUBLISHER]

This paper proposes a frequency-agile Doherty amplifier capable of efficiently amplifying multiband wireless signals located at widely spaced frequencies. Starting with the study of the load modulation concept in the Doherty technique and the various frequency-dependent components involved in its realization, this paper suggests a simplified and effective design methodology for the development of frequency-agile and reconfigurable Doherty amplifiers using a small number of electronically tunable devices. As a proof of concept, a reconfigurable Doherty power amplifier (PA) prototype is designed and fabricated to operate at 1.9, 2.14, and 2.6 GHz. The measurement results obtained using a continuous-wave signal revealed drain efficiencies of approximately 70% and 60% at the peak power and 6 dB back-off power, respectively, for the three targeted operating frequencies. In addition, the reconfigurable Doherty amplifier was successfully linearized when driven with 20-MHz wavelength code-division multiple access and longterm evolution signals, using a Volterra-based digital predistrtion algorithm which exploits a pruned Volterra series. [ABSTRACT FROM AUTHOR]

Practical implementation of monolithic hybrid transformer duplexers have been limited by the poor common-mode isolation. In this paper, a differential hybrid transformer duplexer that covers 3GPP bands I, II, III, and IX between 1.7 and 2.2 GHz is introduced. It achieves a differential to differential isolation of 60 dB in the transmit (TX) band and 40 dB in the receive (RX) band, and a differential to common-mode isolation of 60 dB in both bands. The duplexer with a cascaded low-noise amplifier (LNA) achieves a noise figure of 5.6 dB in the RX path and an insertion loss of 3.7 dB in the TX path. The duplexer and LNA are implemented in a 90-nm CMOS process, consume 20 mA, and occupy an active area of 0.6 \ mm^2. [ABSTRACT FROM AUTHOR]

Recently, X-parameters have been introduced to model active device nonlinear behavior. In addition to providing a measurement-based tool to numerically predict nonlinear device behavior in computer-aided design, they can also provide the designer of nonlinear circuits an analytical design tool. Exploiting this design tool aspect, this work presents an application that combines the nonlinear vector network analyzer PNA-X and a passive tuner to extract a transistor load-independent X-parameter model, focused around targeted circuit impedances for optimal performance. Furthermore, an experimental search algorithm, based on X-parameters analytical computations and developed by Peláez-Pérez , has been used and experimentally validated in this paper, aimed to speed up the characterization and design process, minimizing the number of load–pull measurements necessary to provide an accurate transistor X-parameter model for use in analytical and/or numerical circuit design. [ABSTRACT FROM PUBLISHER]

Two high selectivity fifth-order wideband bandpass filters (BPFs) with multiple transmission zeros based on transversal signal-interaction concepts are proposed in this paper. Two transmission paths consisting of a shorted stub and two open coupled lines are used to realize signal transmission from Port 1 to Port 2. Two fifth-order wideband passbands with six and ten transmission zeros from 0 GHz to 2f0 (f0 is center frequency of the passband) can be achieved respectively due to the superposition of signals of the two transmission paths. Two prototypes with 3-dB fractional bandwidths of 61.7% (2.07–3.92 GHz) and 48.2% (2.3–3.76 GHz) are designed and fabricated for demonstration. Good agreement can be observed between simulated and measured performances. [ABSTRACT FROM AUTHOR]

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]

This paper is focused on the design of generalized composite right/left handed (CRLH) transmission lines in a fully planar configuration, that is, without the use of surface-mount components. These artificial lines exhibit multiple, alternating backward and forward-transmission bands, and are therefore useful for the synthesis of multi-band microwave components. Specifically, a quad-band power splitter, a quad-band branch line hybrid coupler and a dual-bandpass filter, all of them based on fourth-order CRLH lines (i.e., lines exhibiting 2 left-handed and 2 right-handed bands alternating), are presented in this paper. The accurate circuit models, including parasitics, of the structures under consideration (based on electrically small planar resonators), as well as the detailed procedure for the synthesis of these lines using such circuit models, are given. It will be shown that satisfactory results in terms of performance and size can be obtained through the proposed approach, fully compatible with planar technology. [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]

This paper provides a theoretical framework for passivity characterization of symmetric rational macromodels. These may be obtained for linear and time-invariant reciprocal structures if structural symmetry is preserved during the rational fitting stage of the macromodel generation. Standard Hamiltonian-based methods can be used to characterize any passivity violation of such macromodels. Recent developments have suggested, however, that the same results may be obtained at a reduced computational cost, using so-called "half-size" passivity test matrices. In this paper, we generalize such results by providing a complete theoretical framework. In addition to imaginary Hamiltonian eigenvalues, we present a complete characterization of associated eigenvectors, allowing for precise localization of passivity violations. Since half-size matrices are also used for computing the eigenvectors, the overall computational cost is reduced up to a factor of eight. Several numerical examples validate and confirm the theoretical developments. [ABSTRACT FROM AUTHOR]

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

In this paper, a 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]

This paper introduces a one-port method for estimating model parameters of vector network analyzer calibration standards. The method involves measuring the standards through an asymmetrical passive network connected in direct mode and then in reverse mode, and using these measurements to compute the S-parameters of the network. The free parameters of the calibration standards are estimated by minimizing a figure of merit based on the expected equality of the S-parameters of the network when used in direct and reverse modes. The capabilities of the method are demonstrated through simulations, and real measurements are used to estimate the actual offset delay of a 50- \Omega calibration load that is assigned zero delay by the manufacturer. The estimated delay is 38.8 ps with a $1\sigma $ uncertainty of 2.1 ps for this particular load. This result is verified through measurements of a terminated airline. The measurements agree better with theoretical models of the airline when the reference plane is calibrated using the new estimate for the load delay. [ABSTRACT FROM PUBLISHER]

This paper presents a high-efficiency gallium nitride Doherty power amplifier (DPA) using an integrated compensating reactance (CR) for broadband operation. With an additional quarter-wavelength transmission line integrated in the peaking amplifier output, a CR is generated to compensate the load impedance of the carrier amplifier in the low-power region and thus enhance the back-off efficiency over a wide frequency range without affecting the Doherty load modulation at saturation. For this purpose, a peaking output matching network (OMN) is employed to convert the output impedance of the peaking device into quasi-short circuit when it is off and achieve proper impedance matching when it is on. A two-point matching technique using the transmission ( $ABCD$ ) matrix is employed to design such desired OMN. Measurement results show that the DPA has a 6-dB back-off efficiency of 50%–55% and a saturated efficiency of 57%–71% over the frequency band of 1.7–2.8 GHz (49% fractional bandwidth). When driven by a 20-MHz long term evolution modulated signal at 6.5-dB back-off power, the DPA can achieve an average efficiency of more than 50% with high linearity after linearization over the design frequency band. [ABSTRACT FROM PUBLISHER]

This paper presents an integrated four-way power-combining multiplier for 200–230-GHz applications in an advanced 90-nm silicon germanium HBT technology. The active multiplier is implemented using balanced transistor pairs driven by pseudodifferential power amplifiers (PAs) at 100–120 GHz and the outputs at 200–240 GHz are power combined using reactive $\lambda $ /4 impedance transformation networks. A single multiplier breakout results in an output power of 1.8 dBm at 245 GHz with a peak conversion gain of −15.5 dB. The power-combining multiplier achieves an output power of 8 dBm at 215 GHz and >5 dBm at 200–230 GHz. A peak conversion gain of 1.6 dB is achieved at an output power of $\sim 0$ dBm at 215 GHz. The four-way combined multiplier occupies 3.63 mm2, including pads, and consumes 1.2 A from a 1.8 V supply mainly due to the differential 100–120-GHz PAs. To the best of our knowledge, this is the highest output power achieved in multipliers and amplifiers among all silicon-based technology to-date at frequencies above 200 GHz and with a record wide bandwidth. [ABSTRACT FROM PUBLISHER]

This paper presents the implementation of a broadband quasi-circulator through a cascading distributed balun using a 90-nm CMOS process. The isolation, \vert \textS31\vert , of the proposed three-port quasi-circulator can be acquired through the phase cancelation technique, by connecting an additional distributed amplifier in parallel between ports 1 and 3. The thorough analysis based on an eight-port chain matrix and scattering matrix is presented for refining the circuit parameters in the initial design. Measured results show that the proposed quasi-circulator attains a broad operation bandwidth ranging from 10 to 67 GHz. Moreover, the quasi-circulator also has good insertion gain of 0.5 to 4.8 dB, as well as isolation \vert \textS31\vert , which is better than 23 dB. Consequently, the proposed quasi-circulator delivers wide bandwidth performance, good port-to-port isolations, good insertion gain, and high linearity based on the cascading distributed balun with phase cancelation technique. [ABSTRACT FROM PUBLISHER]

This paper proposes accurate CMOS device de-embedding and modeling methods. For millimeter-wave circuit design, accurate simulation models are required. For this reason, an accurate measurement is a key technique for device characterization, and de-embedding and modeling methods are also very important. In this work, a three-parameter pad model based on L-2L de-embedding method and a transistor model with frequency and bias dependency are proposed. The pad model is derived from the assumption that the capacitance of PADs becomes constant at high frequencies. In the transistor modeling, parasitic elements are extracted mathematically. A five-stage low-noise amplifier is fabricated by 65–nm CMOS technology to confirm the accuracy of simulation, and the simulation and measurement results match well with each other. [ABSTRACT FROM AUTHOR]

This paper presents a general sequentially coupled wideband bandpass filter and its direct synthesis and design theory. The filter can achieve the same number of controllable transmission zeros (TZs) as that of resonators above the passband. Each resonator consists of a pair of shunt connected capacitively loaded stub and a grounded inductive stub. Resonators are connected through a short section of transmission line with designated electric length. The short connecting lines allow the filter a wide spurious free stopband. For given specifications and prescribed TZs, the elementary lumped element circuit model can be directly synthesized. Three basic lumped element circuit building blocks are approximated by legitimate distributed element circuits with which the wideband distributed element circuit can be systematically obtained. To demonstrate the performance of the proposed filter configuration and the effectiveness of the developed theory, a fourth and an eighth order of filter prototypes were designed and measured, showing the promising potential for practical applications. [ABSTRACT FROM PUBLISHER]

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]

This paper presents a millimeter-wave (mm-wave) packaging design for E-band long-haul point-to-point communications. A broadband flip-chip interconnect with standard \75~\mu\m pad pitch is developed on an alumina substrate. To meet the application requirement, a microstrip line to WR-12 waveguide (WG) transition is proposed. The transition has no back-short cavity or modified WG involved. A back-to-back transition measurement is conducted to characterize the performance. Results show that the working bandwidth is from 69.5 to 87 GHz and the insertion loss at 77 GHz is less than 0.5 dB. A 40-nm CMOS power amplifier is packaged and measured with the proposed packaging design. The entire packaging loss is only 2.5 dB from pads to WG, including the loss of a 10-mm microstrip line. The simulated and measured results are in good agreement. The gain and peak output power are 13.4 dB and 17.6 dBm. The silicon temperature is measured as \44.4 ^\circ\C after saturated output for 30 min. The performance is close to probe measurement after deembedding the packaging loss. Comparison between bondwire and flip-chip packaging is discussed and both are verified in mm-wave packaging design. [ABSTRACT FROM PUBLISHER]

In this paper, a new characterization method, which allows the determination of the time constants of traps in AlGaN/GaN high electron-mobility transistors is proposed. The approach is based on the current transient method for assessing the time constants that are involved in real working conditions. To do that the dc filling pulses, which are classically used in this method, are replaced by RF filling pulses, which reproduce the real large-signal conditions. To investigate the impact of large-signal working conditions on the trapping phenomena, on-wafer single-pulse load–pull characterizations are carried out at different temperatures and for two different output load impedances: maximum of power-added efficiency and mismatched impedance. The results obtained show the deep impact of the load-line excursion on the current collapse of the detrapping drain current. A comparison between the single-pulse RF load–pull characterization and single-pulse dc measurement is finally presented. [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]

Tensor impedance transmitarrays consist of tensor impedance surfaces, separated by dielectric spacers. In this paper, we present a design method for realizing tensor impedance transmitarrays that are capable of controlling the reflection and transmission of circularly polarized waves, referred to as chiral polarization control. To achieve this, we implement a multi-conductor transmission-line (MTL) model to characterize how vertically and horizontally polarized waves are transmitted and reflected through the surface and to synthesize the desired tensor impedances, which comprise the array. Using this MTL model, we show how to synthesize two different chiral transmitarrays. This includes a polarization rotator, which rotates any linear polarization by 90^\circ and a circular polarization selective surface (CPSS), which transmits one hand of circular polarization while reflecting the other. This is verified with full-wave simulation showing that our proposed model works. We also fabricate and measure the CPSS at X-band based on our design procedure. To measure the CPSS, we use a novel four-port quasi-optical system to characterize both the reflection and transmission of vertically and horizontally polarized fields off of the surface. We achieve a good agreement with our simulated results though we have -\1.7 dB more loss than expected due to the use of FR-4 as our substrate. [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 proposes a novel cooperative composite energy harvesting system that consists in the association of a traditional passive UHF Radio Frequency Identification (RFID) chip with an Electromagnetic Energy Harvesting Circuit (EEH-C). The objective is to exploit the i-v nonlinearity of the rectifier by applying a signal with time-varying envelope in order to improve the RF-to-dc conversion efficiency. Thanks to a multisource configuration, i.e., an RFID reader at 0.868 GHz and an external source at 2.45 GHz, the EEH-C is able to rectify the 3^rd harmonic product of the RFID chip, in addition to the 2.45 GHz signal, without compromising the RFID communication. Additionally, digitally modulated signals are used at 2.45 GHz to further enhance the harvesting efficiency of the EEH-C. From theory, simulations and measurement it is demonstrated that the exploitation of the three nonlinear effects of rectifying circuits, i.e., (i) impedance power dependency, (ii) harmonic signals production, and (iii) waveform dependency can greatly improve the conversion efficiency of the EEH-C. [ABSTRACT FROM PUBLISHER]

This paper presents the design and characterization of dc–dc converters operating at microwave frequencies. The converters are based on GaN transistor class-E power amplifiers (PAs) and rectifiers. Three topologies are presented, which are: 1) a PA and synchronous rectifier, requiring two RF inputs; 2) a PA and self-synchronous rectifier with a single RF input; and 3) a power oscillator with a self-synchronous rectifier with no required RF inputs. The synchronous 1.2-GHz class-\E^2 converter reaches a maximum efficiency of 72% at 4.6 W. By replacing the RF input at the rectifier gate with a specific termination, a self-synchronous circuit demonstrates 75% efficiency at 4.6 W, with a maximum output power of 13 W at 58% efficiency. In the third topology, the PA is replaced by a power oscillator by providing correct feedback for class-E operation, resulting in a circuit requiring no RF inputs. This oscillating self-synchronous dc–dc converter is demonstrated at 900 MHz with an efficiency of 79% at 28 V and 12.8-W output power. Self-synchronous class-E transistor rectifier operation is analyzed theoretically in the time domain and validated with harmonic-balance simulations using an improved nonlinear model for a GaN HEMT. The simplified theoretical analysis provides a useful starting point for high-efficiency self-synchronous power rectifier design, which can, in turn, be extended to high-efficiency oscillating power inverter design. [ABSTRACT FROM AUTHOR]

A method for the design of a new class of distributed low-pass filters enables exact realization of the series short-circuited transmission lines, which are normally approximated via unit elements in other filter realizations. The filters are based upon basic sections using a pair of coupled lines, which are terminated at one end in open-circuited stubs. The approach enables realization of transmission zeros at the quarter-wave frequency, hence giving improved stopband performance. A complete design theory starting from a distributed generalized Chebyshev low-pass prototype filter is presented. A design example demonstrates excellent performance in good agreement with theory. [ABSTRACT FROM AUTHOR]

This paper reports a fully integrated 40-nm CMOS power amplifier (PA) for E-band applications. A neutralized bootstrapped cascode amplifier (NBCA) topology is proposed to enhance the power gain and output power at millimeter wave (mm-Wave) frequencies while maintaining the stability. A broadband 4-way differential parallel-series power combiner is employed to further increase the output power. Besides, both interstage and input passive networks are optimized to improve the bandwidth and common-mode stability. Occupying 0.25 mm^2, the proposed PA achieves a measured output power of 22.6 dBm with 19.3% peak power-added efficiency (PAEMAX). The 2-stage PA has a measured power gain of 25.3 dB. [ABSTRACT FROM PUBLISHER]

In order to realize series-fed millimeter-wave hollow waveguide array antennas, small slots or holes can be used to couple a defined amount of power from the main feed line to the radiating elements. Due to the small size of these structures, they are challenging to manufacture. Moreover, if the size of the required slots or holes are smaller than the available drill, they are not realizable at all. This paper describes a coupling structure, which uses laser-cutting to realize a small slot, while all the other parts of the waveguide circuit can be milled in split-block technology. A deployment in harsh environments such as fusion experiments is feasible, as the whole structure can be built from metal. By design, it is possible to configure the coupling slots, and thus, adjust or modify the tapering of the array antenna. A theoretical model of the proposed structure is given and measurements of W-band prototypes are presented. The manufactured slots achieve coupling factors ranging from -\24.2 dB to -\9.4 dB. Measurements prove the applicability of the proposed design in broadband feed networks as the coupling values are nearly frequency independent with a deviation from the mean coupling ranging from \pm \0.6 dB to \pm \0.9 dB in the whole W-band. The maximum phase variability between the evaluated slots is \pm \10^\circ . [ABSTRACT FROM PUBLISHER]

This paper presents a controllable mode design method for a concurrent dual-mode power amplifier (PA). The principle of the controllable mode combination is proposed by investigating the characteristics of different highly efficient PA modes, which is analyzed from frequency response of the low-pass matching circuit. Then a dual-mode PA with Class-\bf F^-\bf 1 and Class-J mode is taken for example to verify this mode combination concept. A GaN device PA with 10-W output is designed at two frequency ranges of 1.9\sim2.0 GHz and 2.3\sim2.6 GHz. Measurement results show an output power of 40.2\sim42.9 dBm and drain efficiency of 75.6\sim80.3% and 76.6\sim68.8% in two frequency bands. It also provides a broadband operation with drain efficiency of 60\sim80.3% over 1.7\sim2.8 GHz. To evaluate its modulated signal performance with concurrent multiband and broadband applications, dual-band signals (20 MHz + 20 MHz) with 140- and 300-MHz frequency spacing and 100-MHz long-term evolution advanced (LTE-A) signals at two modes are both employed. With digital pre-distortion algorithm, adjacent channel leakage ratio lower than -47.5, -48.6 and -46.1 dBc are achieved, indicating its excellent performance in mobile communication systems. [ABSTRACT FROM PUBLISHER]

In this paper, a multiple stubs loaded ring resonator (MSLRR) is proposed to design directly coupled multi-band bandpass filters (BPFs) with mixed electric and magnetic coupling (MEMC). The proposed MSLRR exhibits multiple-mode resonant behavior. The increased number of loaded stubs excite many more useful resonant modes, but these resonant modes can be still independently controlled. As examples, a dual-band BPF, a tri-band BPF, a quad-band BPF, and a quint-band BPF using different types of MSLRRs are designed and fabricated. The passband frequencies and return losses (RLs) of these multi-band BPFs can be independently controlled. A dual-mode open loop resonator is then introduced in the quint-band BPF to enhance the sixth resonant mode of the MSLRR to produce the sixth passband so that a sext-band BPF is also presented. Multiple transmission zeros due to the cancelling effect of MEMC and virtual grounds in the MSLRR can be observed around the passbands resulting in sharp passband selectivity and high band-to-band isolation. Moreover, all of the fabricated multi-band BPFs have compact sizes, good RLs, and low insertion losses. Good agreements are observed between the simulated and measured results. [ABSTRACT FROM PUBLISHER]

In emerging and future copper access networks, the trend goes towards exploiting higher transmission bandwidths on shorter twisted-pair cables. Methods to accurately determine relevant transmission-line parameters are a prerequisite to exploit the potential of these short-to-medium range access lines. In this paper, we propose a model-based space-frequency optimization approach initially developed for microwave applications. By utilizing the concept of capacitive length, two major advances are achieved. First, we overcome the requirement of a priori information of physical line length. Second, the number of parameters is reduced compared to prior art. We introduce two estimators to illustrate the concept. A low-complexity estimator with only two parameters per spatial unit primarily targets higher frequencies. A wideband estimator with three parameters per spatial unit extends to the lower frequencies used by operational digital subscriber line services. Performance and limitations of the approach are illustrated by both computer simulations and measurements. [ABSTRACT FROM PUBLISHER]

This paper proposes a design methodology for multi-octave planar push–pull power amplifiers (PPPAs) to tackle the challenges associated with the integration of planar balanced to unbalanced transformers (baluns) with packaged transistors characterized by significant parasitics. This methodology relies on carefully selecting the balun’s placement and adding external matching networks to separately control the odd- and even-mode impedances presented to the power amplifier (PA) to ensure high-efficiency operation over a broad range of frequencies. Proper second harmonic impedances are obtained by placing the balun in close proximity to the transistors’ terminals and repurposing the packaged transistors’ leads into a coupled-line with a high coupling coefficient. Furthermore, adequate odd-mode terminations are realized using broadband matching networks at the unbalanced side of the baluns. Following this methodology, an 85-W PPPA was designed using off-the-shelf packaged gallium–nitride high electron-mobility transistors. The fabricated PA demonstrated drain efficiency and output power above 45% and 46.5 dBm, respectively, over the frequency band spanning from 0.45 to 1.95 GHz. Furthermore, the fabricated PA was successfully linearized using digital predistortion when driven with single- and multi-band modulated signals. Overall, the fabricated PA had the best reported power, efficiency, bandwidth, and second harmonic rejection combination for a multi-octave PPPA designed with input and output baluns using packaged off-the-shelf transistors. [ABSTRACT FROM PUBLISHER]

This paper presents a 77-GHz radar system using a transmitter (Tx) and receiver (Rx) integrated with on-chip waveguide feeders in 65-nm CMOS. The newly proposed on-chip waveguide feeder shows the insertion loss of about 2 dB and more than 30% bandwidth. Additionally, both the Tx and Rx are integrated with internal \times10 frequency multipliers. Therefore, a radar system can be easily implemented without sensitive millimeter-wave packaging technology by mounting the Tx and Rx chips on the waveguide aperture. The interconnections for the low-frequency reference and baseband signals can be realized on the low-cost FR-4 printed circuit board. The radar system shows 9-dBm output power and 13-dB down-conversion gain from the waveguide port. [ABSTRACT FROM PUBLISHER]

This paper presents a novel frequency-agile filtering power divider with constant absolute bandwidth and high selectivity. The proposed design utilizes four coupled resonators to obtain the two functions of power division and filtering. Synthesis of the filtering power divider is carried out and the design guidelines are given. Varactors are then loaded to the resonators to enable frequency tuning. By using capacitors as well as magnetic and electric coupling to obtain required external quality factors and coupling coefficients, a constant absolute bandwidth is maintained when tuning the frequency. To demonstrate the validity of the proposed design, a circuit was fabricated. Experimental results show that the operating frequency can be changed from 0.62 to 0.85 GHz with the 3-dB absolute bandwidth of 60 \pm 2.5 MHz. Moreover, transmission zeros are generated near the passband, resulting in high selectivity for each tuning state. Comparisons between the measured and simulated results are presented and good agreement is observed. [ABSTRACT FROM PUBLISHER]