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In this paper, an area-efficient LNA with on-chip input matching circuit utilizing an active inductor is presented. The active inductor is implemented based on the gyrator structure and its noise is improved by employing a feed-forward path (FFP). The overall low-noise performance of the LNA is achieved by cancelling the inductor noise through an additional FFP. It is shown that the proposed LNA circuit is capable of achieving low-noise performance with wideband tuning at the input in a small die area. A 0.32- to 1-GHz LNA has been designed and fabricated in a standard 0.18-\mum CMOS technology. The LNA occupies a die area of less than 0.1 mm^2. The measured results show noise figure of 2.2–2.7 dB (2.2–2.4 dB for the UHF band), return loss of better than 10 dB (13 dB for the UHF band), and voltage gain of higher than 18 dB over the entire frequency band. The LNA draws 8.5 mA from a 1.8-V supply. [ABSTRACT FROM PUBLISHER]

A novel dual-band coupled-line coupler with an arbitrary coupling coefficient is proposed and investigated in this paper. The coupler has a simple structure and can realize a wide range of the same coupling coefficient over two designated frequencies. The mathematical design formula is also developed, which not only provides a straightforward design procedure, but also reveals the attractive features of the proposed coupler, including: 1) the same coupling coefficient in the dual frequency bands; 2) the sole dependence of a coupling coefficient on the ratio of the impedances of even and odd modes; and 3) a large range of the ratio of the dual frequencies. Two prototypes of the proposed couplers, one operating at 2.4/5.8 GHz with a -\10-dB coupling coefficient and the other working at 0.9/1.8 GHz with a -\15-dB coupling coefficient, have been designed, fabricated, and measured. The measured results demonstrate that the bandwidths for the 2.4- and 5.8-GHz bands are 22% and 19.8%, respectively, and that for the 0.9- and 1.8-GHz bands are 28.4% and 15.8%, respectively. Good correlation between the measured results and those of the theoretically designed justifies the proposed coupler circuit and the design theory. [ABSTRACT FROM PUBLISHER]

This paper presents a multi-channel frequency-modulated continuous-wave (FMCW) radar sensor operating in the frequency range from 91 to 97 GHz. The millimeter-wave radar sensor utilizes an SiGe chipset comprising a single signal-generation chip and multiple monostatic transceiver (TRX) chips, which are based on a 200-GHz fT HBT technology. The front end is built on an RF soft substrate in chip-on-board technology and employs a nonuniformly distributed antenna array to improve the angular resolution. The synthesis of ten virtual antennas achieved by a multiple-input multiple-output technique allows the virtual array aperture to be maximized. The fundamental-wave voltage-controlled oscillator achieves a single-sideband phase noise of -\88 dBc/Hz at 1-MHz offset frequency. The TX provides a saturated output power of 6.5 dBm, and the mixer within the TRX achieves a gain and a double sideband noise figure of 11.5 and 12 dB, respectively. Possible applications include radar sensing for range and angle detection, material characterization, and imaging. [ABSTRACT FROM AUTHOR]

In this paper, W-band flip-chip-assembled CMOS chip modules with transition compensation are presented, a three-stage amplifier, a balanced amplifier, and a down-converted Gilbert-cell subharmonic mixer are included in the chip set. The flip-chip process on ceramic integrated passive devices (CIPD) with a bump size of 30 \mum \,\times\,30 \mum \,\times\,27 \mum is developed for millimeter-wave applications. Without the flip-chip transition compensation, the frequency of the return loss of each chip is shifted, which deviates from the bare die measurement results. By applying the compensation network in the transition, the dips of the return loss are tuned back closer to the bare die measurement results. Moreover, a W-band amplifier flip-chip-assembled with a CPW-fed Yagi–Uda antenna on a CIPD and a W-band flip-chip-assembled receiver are presented for SiP integration. The effect of dicing edge variation is also included in the flip-chip model to achieve reasonable agreement between simulated and measured scattering parameters. To the best of our knowledge, this is the first demonstration of a CMOS chip set with flip-chip interconnects in the W-band for a system-in-package. [ABSTRACT FROM AUTHOR]

This paper introduces a novel method to generate an auxiliary third-order intermodulation (IM3) signal, which can be used in the linearization of power amplifiers (PAs) by canceling the output IM3 power. This auxiliary signal is simply achieved by exploiting the input reflected power of the main device, rather than obtained by conventional methods as driving a highly nonlinear device or subtracting the fundamental power from the output signal. It is demonstrated that substantial IM3 power can be reflected to the source with little reflected fundamental power under some input matching conditions of the device, and this feature can be utilized in the design of monolithic microwave integrated circuits (MMICs) targeting excellent linearity. A 25-GHz pHEMT power amplifier is designed and fabricated to exemplify the proposed technique. With the linearization, the OIP3 of the proposed PA increases by 14 dB from 25 to 39 dBm, and the output power enhances significantly, from 5 to 14 dBm with -40-dBc IM3 distortion and from 9 to 14 dBm with -40-dBc adjacent channel power ratio. [ABSTRACT FROM AUTHOR]

In this paper, a compact vital signal sensing method using oscillation frequency deviation at 2.4-GHz industrial–scientific–medical band is proposed to detect vital signals, such as heartbeat and respiration signal. The oscillation circuit of the proposed vital sensor system has been realized by a planar resonator, which functions as a positive feedback element, as well as a near-field radiator to sense vital signals, simultaneously. The periodic movement of a body by respiration exercise causes the impedance variation of the radiator within the near-field range. The impedance variation results in a corresponding change in the oscillation frequency, and this variation has been utilized for sensing of the vital signals. In addition, a surface acoustic wave filter and power detector have been used to increase the sensitivity of the system and to transform the frequency variation to voltage waveform. The experimental results show that the proposed vital sensor placed 20 mm from the body can detect the heartbeat waveform very accurately. [ABSTRACT FROM AUTHOR]

A novel wideband receiver RF front-end, including a resistive negative feedback wideband low-noise amplifier (LNA) with feedforward noise and distortion cancellation and a current commutating down conversion passive mixer with biquad trans-impedance amplifier, is presented in this paper. In comparison to conventional resistive negative feedback LNAs, theory analysis and experimental results for the proposed LNA circuit shows improved performance parameters, including voltage gain, noise figure (NF), and input-referred third-order intercept point (IIP3), especially helpful for wideband LNA design in modern deep-submicrometer CMOS. A wideband receiver RF front-end fabricated in 0.13-\mu\m CMOS, based on the proposed feedforward noise and distortion-cancellation resistive-feedback LNA, has 42–48-dB conversion gain with 0.8–12-MHz tunable IF -3-dB bandwidth and 12-dB adjacent channel selectivity at 2fp, -14-dBm IIP3, and 3-dB NF double-sideband with 10-kHz flicker-noise corner frequency. [ABSTRACT FROM AUTHOR]

This paper demonstrates extremely miniaturized bandpass filters based on asymmetric coupled lines and equal reactance. By reactively loading asymmetric coupled lines while the first and the last inverters are eliminated, the proposed method overcomes the limitation of previous methods to achieve extreme miniaturization. Furthermore, the utilization of asymmetric coupled lines allows the method to miniaturize a filter with equal reactance, which provides a great advantage of low-cost fabrication. A complete set of design equations for an arbitrary number of filter order is provided for both shunt-capacitive and series-inductive loading methods. Experimental results for various miniaturized filters at 0.9 GHz are provided. An unprecedented miniaturization rate of more than 91% is demonstrated for a third-order parallel coupled-line filter. [ABSTRACT FROM AUTHOR]

In this paper, a passive half-quadrature hybrid (HQH) is presented for multiphase signal generation at radio frequencies. Utilizing capacitance ratios as the primary design parameters, the proposed hybrid exhibits excellent magnitude and phase balance even in the presence of process and temperature variations. Therefore, it is well suited for integrated-circuit designs with on-chip capacitive elements. Using a standard 0.18-\mu\ m CMOS process, the HQH circuit is integrated with a 5.6-GHz quadrature voltage-controlled oscillator (QVCO) and four down-conversion mixers for demonstration. As the QVCO oscillation frequency sweeps from 5.4 to 5.8 GHz, the measurement results indicate a root-mean-square (rms) magnitude error less than 0.5 dB and an rms phase error ranging from 4^\circ to 7^\circ at the half-quadrature outputs without any feedback correction. [ABSTRACT FROM PUBLISHER]

A comprehensive method of designing a broadband Doherty power amplifier is presented in this paper. The essential limitations of bandwidth extension of a Doherty power amplifier are discussed based on the proposed structure of the Doherty power amplifier, which also takes the output matching networks of both sub-amplifiers into account. The broadband matching is realized by applying the simplified real frequency technique with the desired frequency-dependent optimum impedances. GaN transistors were selected to implement the circuit structure. [ABSTRACT FROM PUBLISHER]

This paper presents the design of a direct-injection divide-by-3 frequency divider operating at the K-band. The divider is implemented in a 0.18-\mu\ m CMOS process. The measured free-running frequency of the divider is 7.96 GHz. By utilizing a floating-source differential injector and without a varactor tuning in the divider core, the total locking range is 3.2 GHz with a power consumption of 8.28 mW from a supply voltage of 0.9 V. The total power consumption of the buffers is 9.54 mW from a supply voltage of 1.8 V. The measured phase noise of the divider is -141.3 dBc/Hz at 1-MHz offset when the input referred signal with a phase noise of -132.8 dBc/Hz at 1-MHz offset from 24 GHz. The phase-noise difference of 8.5 dB is close to the theoretical value of 9.5 dB for division-by-3. The output power of the divider is more than -11 dBm over the whole locking range. [ABSTRACT FROM PUBLISHER]

This paper presents a 17 GHz to 35 GHz broadband power amplifier (PA) using 0.15-\mum GaAs pHEMT technology. The synthesized transformer using microstrip line matching technique is proposed in this PA design to enhance the broadband frequency response and minimize the chip size. The design procedures are also presented. A high efficiency broadband PA in commercial 0.15 \mum GaAs pHEMT process with the best P1\,dBof 22 dBm, Psat of 23.5 dBm, and PAE of 40% are demonstrated to verify the design concepts. This PA has the highest PAE, smallest chip size, and wide fractional bandwidth among the broadband GaAs HEMT PAs from K to Ka band. [ABSTRACT FROM PUBLISHER]

When solving the transmission-line equations using high-order finite-difference methods, it is extremely important to have appropriate procedures to enforce boundary conditions as well as the continuity of the fields at material interfaces where the material parameters are discontinuous. This paper presents general procedures to accomplish these two tasks on both uniform and nonuniform grids. The proposed procedures can be used to achieve high-order convergence on coarse grids even in the extreme case of analyzing a dispersive Lorentz material interfaced with vacuum and excited at the plasma frequency of the Lorentz material. [ABSTRACT FROM PUBLISHER]

In this paper, the design and fabrication of a miniaturized 4-W power amplifier for the WiMAX frequency band (\2.3-\2.7∼\GHz) is presented. The selected active device is a commercially available GaN HEMT chip from TriQuint Semiconducotr Inc., Hillsboro, OR. The optimum input and output impedances of the GaN HEMT at fundamental frequency are extracted using a custom designed tuning jig. A novel output matching network for class-F operation is proposed and designed using the measured impedances. For integration in a small package, the input and output matching networks are implemented using spiral inductors and interdigital capacitors, and their dimensions were determined using electromagnetic simulation. The fabricated power amplifier is \ 4.4\times \ 4.4∼\ mm^2 and has an efficiency above 50% and harmonic suppression above 40 dBc for second and third harmonics at an output power of 36 dBm. [ABSTRACT FROM AUTHOR]

A novel fast switching noise-cancelling low-noise amplifier (LNA) is presented in this paper using 0.13-\mum CMOS for 3.1–10.6-GHz ultra-wideband applications. A new noise-cancelling topology is employed to simultaneously achieve a sub-4-dB flat noise figure and a high gain of 16.6 dB for frequencies up to 10 GHz. Fast on and off power switching is achieved by bypassing the large dc-bias resistors that lead to long charging time constants, allowing the output voltage to settle within only 1.3 ns for switching frequencies as high as 200 MHz. The phase noise and jitter added by the switched LNA was characterized, and the measured output integrated rms jitter is about 750 fs from 10 Hz to 1 MHz, while the input integrated rms jitter is 420 fs. The circuit consumes 18 mW of dc power in the on state. When the circuit is switched on and off with a 50% duty cycle, the power consumption is less than 10 mW. It occupies an active chip area of less than 0.5 mm^2. [ABSTRACT FROM PUBLISHER]

A new methodology for designing and implementing high-efficiency broadband Class-E power amplifiers (PAs) using high-order low-pass filter-prototype is proposed in this paper. A GaN transistor is used in this work, which is carefully modeled and characterized to prescribe the optimal output impedance for the broadband Class-E operation. A sixth-order low-pass filter-matching network is designed and implemented for the output matching, which provides optimized fundamental and harmonic impedances within an octave bandwidth (L-band). Simulation and experimental results show that an optimal Class-E PA is realized from 1.2 to 2 GHz (50%) with a measured efficiency of 80%–89%, which is the highest reported today for such a bandwidth. An overall PA bandwidth of 0.9–2.2 GHz (84%) is measured with 10–20-W output power, 10–13-dB gain, and 63%–89% efficiency throughout the band. Furthermore, the Class-E PA is characterized through measurements using constant-envelop global system for mobile communications signals, indicating a favorable adjacent channel power ratio from -40 to -50 dBc within the entire bandwidth. [ABSTRACT FROM PUBLISHER]

This paper presents a modified parallel-circuit class-E amplifier that accommodates devices with larger output capacitances, recovering the class-E operating conditions. The finite inductor in the parallel circuit topology is replaced by a more suitable network composed of a series inductor and additional subharmonic resonators. Analysis of the class-E amplifier allows to determine the required frequency-domain response of this new network. Derivation of the circuit elements of the proposed network is shown in detail, and a design procedure for this modified class-E is provided. The analysis is validated by simulation and design of a test board. Measurements of the test board showed a drain efficiency of 80.7%, power-added efficiency of 78.6%, and output power of 4.91 W at 434 MHz, exhibiting levels of efficiency similar to that obtained by other amplifiers using the same device, but at much lower frequencies. According to the authors' knowledge, this study represents the first systematic approach to design class-E power amplifers at UHF using devices with larger COUT by taking into account the use of arbitrary finite-feed class-E topologies. [ABSTRACT FROM PUBLISHER]

In this paper, a digital Doherty power amplifier (PA) with improved efficiency performance over a wide power range is proposed. The efficiency enhancement is achieved by using a digitally controlled dynamic input power distribution scheme implemented to improve the active load modulation mechanism and to minimize the drive power waste into the peaking branch at backed-off power levels. Furthermore, the proposed distribution scheme causes the premature saturation of the carrier amplifier of the proposed Doherty PA and results in an extended range of high back-off efficiency. A comprehensive study of the operational principle of the proposed efficiency-extended digital Doherty PA is provided to demonstrate its merits and to enlighten its operation. In particular, the current and power profiles of the proposed digital Doherty PA are exposed and its efficiency characteristics analyzed. For experimental validation, the proposed Doherty PA is implemented within the dual-input digitally driven architecture based on a 10-W gallium–nitride transistor. Using a one-carrier Worldwide Interoperability for Microwave Access signal with a 9-dB peak-to-average power ratio and 10-MHz bandwidth, the digitally linearized efficiency-extended Doherty PA exhibited an excellent drain efficiency of 50% along with -38 dB of relative constellation error. The efficiency enhancement is 7% in comparison to a conventional fully analog Doherty PA. [ABSTRACT FROM AUTHOR]

New design formulas for impedance-transforming 3-dB Marchand baluns are proposed. They are about the even- and odd-mode impedances of the coupled transmission-line sections of the Marchand baluns and determined by coupling coefficients together with termination impedances. The particular property proposed in this paper is to choose the coupling coefficient arbitrarily, resulting in infinite sets of design formulas available. This is quite different from the conventional design approach in which only one coupling coefficient is possible. For the perfect isolation of the Marchand balun, an isolation circuit (IC) is needed, being composed of two 90^\circ transmission-line sections and resistance(s). Sufficient area to build such a long IC is, however, inherently not available. For this, ways to reduce the IC size are also suggested. To validate them, a microstrip Marchand balun terminated in 130 and 70 \Omega is designed at a design center frequency of 1.5 GHz and tested. The measured results are in good agreement with prediction, showing that power divisions are 3.57 and 3.262 dB, return losses at all ports are better than 21 dB, and the isolation is better than 20 dB around the design center frequency. The measured phase difference between two balanced signals is \180^\circ\pm \2^\circ in about 50% bandwidth. [ABSTRACT FROM AUTHOR]

In this paper, we propose and develop a partially shielded tunable filter structure using a varactor-loaded split-ring resonator. The novel physical topology of the filter is suitable for vertical stacking of filters and enables a compact multilayer tunable filter for applications requiring a very wide tuning range. The capacitance range and ratio needed to achieve the designated tuning range are presented, and analytical solutions are given for the second and third higher order modes for synthesis in the spurious-free filter operation range. Two prototypes are developed. A partially shielded tunable filter using varactor-loaded split-ring resonators is developed to verify the design method and to demonstrate the wide tuning range of a tunable filter. To further extend the tuning range, a filter bank with three stacked tunable filters at different frequency bands are designed and developed. With slight overlap between neighboring bands, a continuous tuning range of more than 6:1 is achieved. [ABSTRACT FROM AUTHOR]

Recent research has demonstrated the use of plasmonic nanoparticles (e.g., a silver or a gold nanosphere) as circuit elements. In these metallic nanoparticles, an electromagnetic wave at optical frequencies excites conduction electrons resulting in a plasmon resonance. The derived values of circuit components are based on the observation that the small size of the particle compared to the wavelength leads to lumped-impedance representations under the quasi-static approximation. In this paper, we show that circuit representations based on quasi-static approximations can often result in large errors for typical nanosphere sizes. To remedy this issue, we present a new approach based on time-varying fields, which uses vector wave functions to explicitly derive accurate resonance frequency and impedance expressions for these metallic nanospheres at and around the plasmon resonance. In particular, the proposed approach accurately predicts the dependence of the resonance frequency on the size of the nanoparticle and yields more accurate expressions for the equivalent L and C lumped elements compared to the quasi-static model. The new impedance approach is still compatible with the process of cascading nanoparticles in series and parallel combinations to synthesize more complex nanocircuits. A comparison with Mie and full-wave finite-element simulation results demonstrates that our model provides accurate closed-form expressions, thereby extending the range of the impedance representation to larger radii nanoparticles. [ABSTRACT FROM AUTHOR]

In this paper, we present the design of nanostructured multilayer absorbers, carried out with the aid of a genetic algorithm (GA). Waveguide measurements are performed to recover the dielectric properties of micrographite single-walled carbon nanotube, micrographite walled carbon nanotube, carbon nanofiber, and fullerene-based composite materials. Conductive fillers are uniformly dispersed in an epoxy resin at different weight percentages (1, 3, 5 wt.%). The electromagnetic (EM) analysis is performed embedding the forward/backward propagation matrix formalism in an in-house GA, thus able to carry out optimization upon oblique incidence over a finite angular range. Developed code minimizes both the reflection and the transmission coefficients under the thickness minimization constraint. Comparison between micrographite and nanopowders absorbers is presented and discussed, when a broadband quasi-perfect absorber is achieved among the X-band combining the two filler families, i.e., exhibiting a loss factor greater than 90% in most of the band, for a thickness of about 1 cm. It is demonstrated that the nanofillers with higher aspect ratio mainly contribute to the EM absorption. Findings are of interest in both radar-absorbing material and shielding structures. [ABSTRACT FROM AUTHOR]

A design methodology for a concurrent dual-band Doherty power amplifier (PA) with frequency-dependent backoff power ranges is presented in this paper. Based on a dual-band T-shaped network and a coupled line network, different dual-band components needed in Doherty PA topology, including a 3-dB branch-line coupler, an offset line, and a quarter-wavelength transformer, are developed. Two prototypes with balanced and imbalanced backoff power range modes are implemented to verify the feasibility. Continuous wave signal test results show that the proposed dual-band PA successfully achieves a power-added efficiency of 33% and 30% at the 6-dB backoff point from the saturated output power at 880 and 1960 MHz, respectively. To meet linearity requirements, the PA nonlinear behavior is characterized by using digital multitone signals, which categorize the distortions of a concurrent dual-band PA into intermodulation and cross-modulation. Finally, a 2-D digital predistortion technique is used to compensate for the nonlinearity of PA in dual bands. Two two-tone signals are applied to the dual bands for linearization, and the experimental results show that this technique achieves improvements of better than 19.1 and 24.6 dB for the intermodulation and cross-modulation in the dual bands, respectively. [ABSTRACT FROM AUTHOR]

A new dual-band 90° coupler using coupled transmission lines is proposed in this paper. As the coupler consists of only three quarter-wave coupled-line sections, it occupies less circuit area as compared to other existing dual-band branch-line couplers. A desired dual-band operation can be achieved by proper design of the coupling level for those coupled-line sections. Moreover, the coupler's configuration contains a degree of freedom so that its design is “customizable,” allowing itself to be conveniently realized on a variety of circuit and substrate technologies. As a result, it is suitable for use in many practical applications. [ABSTRACT FROM PUBLISHER]

This paper presents a compact highly linear tunable second-order quasi-elliptic filter with constant 3-dB bandwidth. The proposed filter is thoroughly analyzed to clearly describe the filter equivalent circuit and the tuning mechanism involved. In addition, the tunable resonator configuration employed is shown to improve filter linearity, especially for low bias voltages where distortion is normally stronger. A quasi-elliptic tunable filter was designed, built, and tested for illustration and verification. With a 3-dB bandwidth variation of only 4.6%, the filter had a frequency coverage from 1.45 to 1.96 GHz, an insertion loss better than 2.5 dB, and measured IIP3 > 43 dBm throughout. The experimental results are in excellent agreement to theory and simulations. [ABSTRACT FROM PUBLISHER]

This paper proposes a systematic approach for the elimination of spurious oscillations in circuits with multiple active elements. The procedure is based on detecting the sensitive parts (nodes or branches) of the complex circuit at which we can have a strong control of the dynamics responsible for the instability. To do so, stability analyses based on pole-zero identification are performed at multiple observation ports. Once sensitive locations are detected, stabilization is achieved by adding series or shunt stabilization networks at the suitable node or branch. Standard techniques from linear control theory (pole placement strategies) are used to automatically calculate the values of the stabilization elements ensuring circuit stability. Here, the methodology is applied to the stabilization of a two-stage Ku-band high-power amplifier for active antenna space applications. [ABSTRACT FROM AUTHOR]

In this paper, an analysis of a power amplifier manipulated using a second harmonic (PA-2HM) is described using a remarkable correlation between the fundamental and second harmonic impedances. The output loading condition, made up of an optimum fundamental impedance mapped to the conditional second harmonic reactance, allows us to achieve a high-efficiency power amplifier (PA) with a simple output matching circuit. For the analysis, the output voltage and current waveforms are modeled in terms of their output loading in order to extend the output power and efficiency. Specific PA-2HM cases, inverse Class-F and Class-J modes, are analyzed using different second harmonic reactance conditions. The allowable second harmonic reactance for maintaining maximum efficiency has been found to be spread throughout a wide range. To justify the analysis, a harmonic load–pull simulation and measurement are conducted and compared with analysis results. For verification, a commercially available 60-W gallium–nitride (GaN) device was used for different types of PA (inverse Class-F and Class-J) with appropriate second harmonic impedance. In terms of the output power and drain efficiency, the measured results are in good agreement with not only computer-aided design simulations, but also with our analysis and load–pull results. [ABSTRACT FROM AUTHOR]

This paper presents an exact closed-form design method for dual-band unequal Gysel power divider with arbitrary termination resistance. To obtain the unequal property, branch lines with different characteristic impedances attached to a short-circuit terminated stub and an open-circuit terminated stub are needed. Arbitrary termination resistance matching can be achieved without additional output transformers. Line impedance analysis shows the proposed structure can support large power-dividing ratio (up to 6) with wide frequency ratio range (1.5–2.4). Power operation analysis shows that it maintains Gysel divider's high power-handling advantage over Wilkinson divider. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical method to design a dual-band filter using the short-circuit terminated half-wavelength stepped-impedance resonator (SIR). The SIR has an advantage to easily control the first and second resonances by adjusting its structural parameters. In the proposed method, the structural parameters of the SIR are obtained analytically according to the two passband center frequencies and bandwidths of the filter. As a result, the achievable specifications of the dual-band filter can be rapidly determined. The coupling between adjacent SIRs is realized by a short-circuited stub, which is characterized as a K-inverter network. The dual-frequency transformer incorporated with the tapped-line input/output structure is used for the external coupling. Applying the analytical equations in the design process, a dual-band filter can be easily and quickly realized. More importantly, compared to the published dual-band filters, the proposed method is easier to design, especially for a relatively high-order dual-band filter. Two fourth-order and one sixth-order dual-band filters are designed and fabricated to demonstrate the proposed method. [ABSTRACT FROM PUBLISHER]

In this paper, a high-efficiency envelope-tracking (ET) transmitter incorporating a novel efficiency-boosting function is proposed and implemented. An inverse Class-F power amplifier is utilized and optimized using the proposed output loading condition, which enhances its efficiency at the high probability region. This matching network can be conveniently implemented by controlling the nonlinear capacitance of the power transistor. For an accurate analysis, the output waveforms are modeled in terms of the nonlinear capacitance, and the efficiency and output power are subsequently analyzed and successfully optimized. For a high-efficiency envelope amplifier (EA), we propose a new EA utilizing a 2-bit switching stage in place of a 1-bit switching stage. This proposed architecture effectively reduces the ripple current, improving the efficiency of the EA. To verify our analysis, we have fully implemented a 3.54-GHz high-efficiency ET transmitter including a digital processing block. The experimental results show that the ET transmitter using a commercial 60-W peak-envelope-power GaN device operates at a drain efficiency of 44% and power-added efficiency of 39.6% with a gain of 10.1 dB at an average output power of 40 dBm for a 10-MHz third-generation long-term evolution signal with 8.5-dB peak-to-average power ratio. Using a digital pre-distortion function, the adjacent channel leakage ratio is less than -\47.5 dBc. [ABSTRACT FROM AUTHOR]

This paper analyzes the noise and gain measurement of microwave differential amplifiers using two passive baluns. A general model of the baluns is considered, including potential losses and phase/amplitude unbalances. This analysis allows de-embedding the actual gain and noise performance of the isolated amplifier by using single-ended measurements of the cascaded system and baluns. Finally, measured results from two amplifier prototypes are used to validate the theoretical principles. [ABSTRACT FROM AUTHOR]

In this paper, compact ultra-wideband (UWB) bandpass filters with ultra-narrow dual- and quad-notched bands are proposed using the broadside-coupled microstrip/coplanar waveguide (CPW) structure. The multiple-modes UWB operation is obtained through the CPW detached-mode resonator (DMR) and broadside-coupled microstrip/CPW transition. To avoid the existing interferences such as the wireless local-area network signals (i.e., 5.2- and 5.8-GHz bands) in the UWB passband simultaneously, dual-notched bands can be finely employed and independently adjusted by the embedded quarter-wavelength (\lambda/4) CPW resonators and the \lambda/4 meander slot-line inserted in the DMR, respectively. To further cancel the interferences from the 3.5-GHz worldwide interoperability for microwave access and 6.8-GHz RF identification communication, the \lambda/4 meander defected microstrip structure is employed. Based on the structures mentioned above, a series of UWB bandpass filters with dual- and quad-notched bands are then designed and fabricated. With good passband/stopband performances, compact size, and low cost, the proposed filters are attractive for the practical applications. [ABSTRACT FROM PUBLISHER]

This paper presents the design, analysis, and measurement of a pseudodifferential distributed power amplifier in a 0.13-\mum SiGe BiCMOS process. To mitigate the large loaded transmission line loss due to bipolar base resistance, emitter degeneration is used and an optimal small-signal design point is selected for maximum gain-bandwidth product. To enhance the efficiency of distributed amplifiers (DAs), a stage-scaling technique is proposed to utilize more voltage swing while reducing the total current consumption. The output power and efficiency of the amplifier are evaluated as a function of two scaling coefficients. The fabricated distributed power amplifier achieves a small-signal gain of 10 dB and a 3-dB bandwidth of 110 GHz. The measured midband saturated output power is 17.5 dBm with a peak power-added efficiency (PAE) of 13.2% and the 3-dB output power bandwidth is greater than 77 GHz. The amplifier consumes 119 mA from a 3-V supply and occupies an area of 2.08 mm \,\times\, 1.05 mm. Compared to a uniform nonscaled DA fabricated in the same process, the stage-scaled amplifier achieves the same output power with higher collector efficiency and PAE over the entire measured frequency range. [ABSTRACT FROM AUTHOR]

The extended continuous class-F mode RF power amplifier (PA) is presented for the first time. The introduction and experimental validation of this novel PA mode demonstrates a new design space over a wide band of frequencies. This paper will show that high output power and drain efficiency, equivalent to the class-F mode, can be maintained by varying the reactive components of fundamental and second harmonic impedances in accordance with the new formulation of the voltage waveform. Additionally it will be shown that, by varying both phase and magnitude of the fundamental and second harmonic impedances, a yet wider design space can be achieved, where the efficiency is maintained at a level greater than a certain target value. For the validation of this new theory, an experimental investigation was carried out on GaAs pseudomorphic HEMT devices and demonstrates that high output power and drain efficiency between 75%–83% can be achieved over a wide range of fundamental and second harmonic loads. [ABSTRACT FROM AUTHOR]

This paper presents a new design of wide slot antenna for various wideband applications. The proposed printed antenna consists of a slot and a turning stub, both formed by a binomial curve function; thus, various bandwidths (BWs) can be obtained based on the structure with different binomial curves. Some key parameters affecting the antenna performance have been analyzed and discussed in detail as an antenna design guideline. To validate the theoretical design, six prototypes of various binomial-curved slot antennas were designed, fabricated, and measured. Good agreement between the simulated results and the measured ones is observed. The results demonstrate that the proposed type of antenna can obtain a BW range from 9.8% to 99.7% for VSWR \leq 2 by selecting various binomial-curved slots, which may provide a convenience for various wideband antenna designs. Moreover, the proposed type of antenna owns a simple structure and a stable gain of about 3–5.5 dBi, which is very suitable for wideband wireless system applications. [ABSTRACT FROM AUTHOR]

A novel way capable of improving low-frequency performance of Vivaldi antennas is presented in this paper. Traditional Vivaldi antennas are modified via introducing the loading structure, i.e., circular-shape-load or slot-load, to match the termination. This modified antenna has been demonstrated to have the impedance bandwidth of over 25:1. It also exhibits symmetric radiation patterns in both the E- and H-plane in addition to the gain varying from 3 to 12 dBi in the measurement bandwidth of 4–50 GHz. [ABSTRACT FROM AUTHOR]

This paper focuses on the analysis and the design methodology of the step-impedance phase-inverter rat-race coupler on a silicon-based process. The issues of impedance limitation and bandwidth are discussed in detail. Our proposed concept utilizes a high silicon dielectric constant, phase-inverter structure, step-impedance technique, and Chebyshev response to make the rat-race coupler more compact (\sim \!\ 64\% reduction) and highly balanced over a wide operating bandwidth. Moreover, the inter-digital coplanar stripline used in the step-impedance section effectively reduces the characteristic impedance of the transmission line for large size shrinkage and insertion-loss reduction. The demonstrated step-impedance rat-race coupler directly on silicon substrate has \ 6-\sim \ 7-\ dB insertion loss from 5 to 15 GHz and small variations in amplitude/phase balance. Compared with our previous work, the proposed rat-race coupler achieves a 3-dB improvement in the insertion loss. Thus, a 0.13-\mu\ m CMOS Gilbert down-converter with a miniature phase-inverter rat-race coupler at the RF path for wideband single-to-differential signal conversion achieves a noise figure of 16 dB. [ABSTRACT FROM AUTHOR]

Net-type resonators with dual- and tri-mode electrical behaviors have been presented and analyzed theoretically in this paper. The proposed net-type resonator is constructed by a short-ended and several open-ended transmission-line sections, which has the advantages of small size and more flexible resonant frequency allocation and is therefore particularly suitable for applications to the design of microwave devices. To verify the usefulness of the proposed resonators, three experimental examples, including a dual-mode bandpass filter, a dual-passband filter, and a triplexer, have been designed and fabricated with microstrip technology. Each of the designed circuits occupies a very small size and has a good upper stopand performance. All measured results are in good agreement with the full-wave simulation results. [ABSTRACT FROM AUTHOR]

In this paper, we conduct a thorough analysis of the nonlinear behavior of diode power probes and demonstrate how memory effects can alter power measurements of signals with wide modulation bandwidths and high values of peak-to-average power ratio. We show analytically, by simulations, and with measurements, that commonly used single-tone calibration procedures for diode power probes can provide erroneous values when measuring modulated signals used in many new wireless standards. We show that high values of peak-to-average-power ratio can degrade the calibration results due to the low-frequency response imposed by the power probe's baseband circuit impedance. This effect is first theoretically demonstrated by use of a Volterra series, and then validated by simulations and measurements with a diode power probe circuit. This study provides engineers with guidelines for techniques for correction of diode power probe measurements. [ABSTRACT FROM AUTHOR]

This paper presents a direct carrier six-port modulator. To allow arbitrary load impedances to be used and for suppression of carrier leakage, a new circuit architecture with a technique to suppress carrier leakage is proposed and implemented. A theoretical model of the proposed modulator is derived. A prototype modulator utilizing diodes for impedance generation is designed and fabricated for a center frequency of 7.5 GHz for verification of the proposed technique. Measurements show good modulation properties when a 16 quadrature amplitude modulation signal at 100 Msymbol/s is generated, as well as good carrier leakage suppression. [ABSTRACT FROM AUTHOR]

In this paper, a single-stage 60-GHz frequency tripler is presented with -\1.1-dB conversion gain in a 0.15-\mu\ m pseudomorphic HEMT process. When the input power backs off, unlike most of its counterparts, the conversion gain of the proposed tripler degrades very little. This feature is achieved by adjusting load impedances independently for the first and third harmonic. Besides the enhancement of the third harmonic power, substantial fundamental power is also generated without additional power consumption and is further used to drive an auxiliary diode tripler. The third harmonic power from the original field-effect transistor (FET) and the auxiliary diode tripler are combined with the conversion gain further enhanced, and the power dynamic range is also extended due to the power contributed from the auxiliary tripler. Quantitative analysis for the harmonic loading effect of the FET tripler and the bias selection for the diode tripler are conducted by using the equivalent-circuit models. The theories are verified by computer-aided design simulations and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents, for the first time, the novel design of a dual-band crossover. The proposed circuit features planar implementation with moderate line impedance, compact layout, and widely separated frequency bands. Moreover, simple and explicit closed-form expressions are available for the exact evaluation of the line impedances. For verification, both simulated and measured results of a microstrip crossover operating at 800 MHz and 1.2 GHz are given. [ABSTRACT FROM AUTHOR]

In this paper a two-stage 2-GHz GaN HEMT amplifier with 15-W output power, 28-dB power gain, and 70% power-added efficiency (PAE) is presented. [ABSTRACT FROM AUTHOR]

Passive RF identification (RFID) tags are traditionally assumed to be downlink limited since typical tag sensitivity is considerably poorer than reader sensitivity, due to stringent power limitations. On the other hand, semipassive tags are generally uplink limited because of improvement in tag sensitivity for battery-assisted tags. In this paper, it is demonstrated that judicious choice and use of integrated circuit impedance for backscatter modulation will be needed to simultaneously maximize tag uplink and downlink ranges as passive tag designs improve. Optimal backscatter modulation indices for amplitude shift keying are derived for range maximization of next-generation low-power RFID tags. [ABSTRACT FROM AUTHOR]

This paper presents an approach to maximize the efficiency of a Doherty power amplifier (PA) with the knee voltage effect. Since the carrier PA with 2Ropt, which is the usual matching impedance for a carrier PA at a low power region, does not reach to the saturated operation at the 6-dB back-off power level, the maximum efficiency could not be achieved. However, the carrier amplifier can be driven into the saturation using the load impedance larger than 2Ropt and can deliver the maximum efficiency even under the knee voltage effect. The optimized design for the maximum efficiency at the back-off level is derived. The optimized amplifier is analyzed and simulated in terms of its load modulation behavior, efficiency, and output power, then compared with the conventional Doherty PA. The enhanced performance is demonstrated by the Doherty PA built using CREE's GaN HEMT CGH40045 devices at 2.655 GHz. For worldwide interoperability for microwave access applications with a 7.8-dB peak-to-average power ratio, the proposed PA delivers an efficiency of 49.3% at an output power of 42 dBm with an acceptable linearity of -23.1 dBc. The linearity is improved to -43 dBc by employing a digital feedback predistortion technique, satisfying the system linearity specification. [ABSTRACT FROM AUTHOR]

New ultra-wideband high-order Marchand baluns with one microstrip unbalanced port and two microstrip balanced ports are proposed in this paper. The proposed Marchand baluns are synthesized based on an S-plane high-pass prototype using the Richards' transformation. The responses of the synthesized high-order Marchand baluns are exactly predicted at all real frequencies. All circuit elements are commensurate, which means the electrical lengths of all transmission line elements are a quarter-wavelength long at the center frequency. Two fifth-order Marchand baluns with reflection coefficients of -20.53 and -21.71 dB corresponding to 131% and 152% bandwidth, respectively, are synthesized and realized using the combinations of microstrip lines, slotlines, and coplanar striplines. Simulated and measured results are presented. [ABSTRACT FROM AUTHOR]

In this paper, differential low-noise amplifiers are presented as a very powerful solution for radio astronomy applications. A fully differential amplifier topology has been analyzed and implemented in microstrip technology with discrete surface mount components. The amplifier design is made for an active receiving dense antenna array. Thus, the differential amplifier source impedance is no longer 50 \Omega, but 150 \Omega from the proposed bunny-ear antennas. A full characterization in terms of gain and noise has been undertaken. Source–pull measurements have been included in order to evaluate the performance of the amplifiers operating with variable source impedances. Noise temperatures below 55 K have been obtained for the differential design in the 300–1000-MHz band for the 150-\Omega impedance. In addition, the results for different scanning angles are also presented. [ABSTRACT FROM AUTHOR]

In this paper, efficiency-limiting physical constraint effects imposed on the knee voltage, along with a variation of the optimum load resistance, are investigated for highly efficient Class-F and Class-\F^\-1 amplifiers. First, for an accurate analysis and comparison, new current waveform models are identified, and a realistic approach incorporated using a nonzero knee voltage and voltage-dependent nonlinear capacitance is employed to derive the voltage waveforms of the amplifiers. An analysis is performed to show the efficiency, output power, power gain, and output power compression points for both modes. Using this knowledge, along with a complete performance comparison, we provide a direction for optimizing the amplifier design. The analytic results are further verified based on the measured results of 3.54-GHz Class-F and Class-\F^\-1 amplifiers using a commercial 60-W peak-to-envelope power gallium–nitride device. The experimental results show that Class-F and Class-\F^\-1 amplifiers operate at drain efficiencies of 69.9% and 69.4% at saturated output powers of 47.4 and 47.2 dBm, respectively. These remarkably similar performances have excellent agreement with the predicted analysis at our operational frequency. [ABSTRACT FROM AUTHOR]

Devices used for biological experiments on cell cultures can present a low impedance. In this paper, a numerical and experimental characterization of a high-voltage, nanosecond-pulse, 10-\Omega generator is proposed. The generator makes use of a combination of microstrip-line technology and laser-triggered photoconductive semiconductor switches that operate in the linear regime. A standard electroporation cuvette is used to load the generator. SPICE and finite-difference time-domain (FDTD) models of the whole setup (i.e., the generator and the cuvette) are developed. Numerical characterization is performed comparing SPICE analysis and FDTD simulations. Experimental characterization on a built prototype is carried out by means of a wideband frequency voltage sensor. A good level of consistency is obtained between the numerical and the experimental voltage intensities measured across the cuvette electrodes. [ABSTRACT FROM AUTHOR]

The problem of interconnect modeling embedded in multilayered substrate is initially formulated in terms of the volume integral equation (IE) with respect to 3-D conduction current density. One out of three degrees of freedom in volumetric current variation is then eliminated by approximating the current behavior over the coordinate normal to the conductor surface according to the skin-effect. The remaining two degrees of freedom in the volumetric current variation constitute the unknown current distribution on the conductor surface for which a governing surface electric field integral equation is obtained directly from the volume IE via restriction of the volumetric operator's range to the conductor surface. The resultant surface IE features a global to the conductor cross section surface impedance operator, which is shown to approximate the relationship between tangential electric and magnetic field components on the conductor surface. The proposed novel surface IE featuring multilayered media dyadic Green's function is amenable to various discretization schemes including the Rao–Wilton–Glisson method of moments. In this paper the latter is implemented by casting the scattered field operator into Michalski–Zheng's mixed-potential form in conjunction with enforcement of global relationships between the basis and testing functions in conductor cross sections according to the surface impedance operator. Numerical comparisons to alternative conductor loss models show that the method achieves volumetric solution accuracy within the framework of a boundary-element formulation. [ABSTRACT FROM AUTHOR]