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The article presents a new nonstatioanry nonlinear discrete model, which can be used for the numerical simulation of a coupled-cavity traveling-wave-tube amplifier. The model is shown to be extremely accurate and advantageous, as compared to the conventional models.

An RF electrostatic discharge (ESD) protection for millimeter-wave (MMW) regime applied to a 60-GHz low-noise amplifier (LNA) in mixed-signal and RF purpose 0.13-[micro]m CMOS technology is demonstrated in this paper. The measured results show that this chip achieves a small signal gain of 20.4 dB and a noise figure (NF) of 8.7 dB at 60 GHz with 65-mW dc power consumption. Without ESD protection, the LNA exhibits a gain of 20.2 dB and an NF of 7.2 dB at 60 GHz. This ESD protection using an impedance isolation method to minimize the RF performance degradation sustains 6.5-kV voltage level of the human body model on the diode and 1.5 kV on the core circuit, which is much higher than that without ESD protection ( Index Terms--CMOS integrated circuits (ICs), low-noise amplifiers (LNAs), millimeter-wave (MMW) circuits, RF electrostatic discharge (ESD) protection.

A method of using low-loss waveguide septum combiners is developed into a high-power Ka-band (31-36 GHz) amplifier producing >50 W at 33 GHz (Ka-band) using 32 low-power (< 2 W) solid-state amplifier modules. By using low-loss waveguide combining and a packaged monolithic microwave integrated circuit with a low-loss microstrip-to-waveguide launcher, the output loss is minimized, allowing for the overall power-combining efficiency to remain high, >80% (average insertion loss of combiner 120 W are possible. The current approach is based on corporate combining, using low-loss waveguide septum combiners that provide isolation, maintaining the true graceful degradation of a modular solid-state amplifier system. Index Terms--Amplifiers, dielectric-loaded waveguides, high-power Ka-band, power combiners, solid state.

This paper realized a broadband uniplanar phase-inverter rat-race coupler using a standard silicon process, and then analyzed this coupler under a lossy condition. A phase inverter is employed in this coupler, not only to extend the operation bandwidth, but also to generate balanced outputs by providing equal lossy paths, while symmetrical spiral-shaped coplanar striplines (CPSs) are also utilized to shrink the coupler size, as well as to construct a phase inverter in the middle of one of spiral CPSs. The lossy CPS, when designed as a distortionless line, has a real characteristic impedance, and thus, perfect port matching of the coupler can be achieved at the center frequency. The operation frequency of this silicon monolithic rat-race coupler with the size of 0.5 [mm.sup.2] is extremely wide and ranges from 5 to 23 GHz. The dissipated loss, transmission coefficient, and isolation of the ratrace coupler are approximately 5.5, -8, and below -25 dB, respectively. In addition, a wideband Gilbert micromixer with an integrated uniplanar phase-inverter rat-race coupler at the local oscillator port is demonstrated using 0.35- [micro]m SiGe BiCMOS technology. This mixer works from 2.5 to 13 GHz with 12-dB conversion gain, -16-dBm [IP.sub.1 dB], -4-dBm [IIP.sub.3], and 14-dB noise figure. The chip size of the mixer with an integrated coupler is approximately 1.4 mm x 1.4 mm. Index Terms--Downconverter, micromixer, phase inverter, rat-race coupler, SiGe BiCMOS, silicon substrate, transimpedance amplifier, wideband.

A MMIC process in AlGaN/GaN technology for advanced transceiver design has been developed. The process is based on microstrip technology with a complete model library of passive elements and AlGaN/GaN HEMTs. The transistor technology in this process is suitable for both power and low noise design, demonstrated with a power density of 5 W/mm, and an NFmin of 1.4 dB at X-band. Process stability of subcircuits, complementary to power amplifiers and LNAs, in a transceiver system have been investigated. The results indicate that an all AlGaN/GaN MMIC transceiver is realizable using this technology. Index Terms--Amplifier, gallium nitride (GaN), mixer, monolithic microwave integrated circuit (MMIC), switch.

A novel modified resistive feedback structure for designing wideband low-noise amplifiers (LNAs) is proposed and demonstrated in this paper. Techniques including feedback through a source follower, an R-C feedback network, a gate peaking inductor inside the feedback loop, and neutralization capacitors are used. Bond-wire inductors and electrostatic devices (ESDs) are co-designed to improve the chip performance. Two LNAs, LNAI and LNA2, were fabricated using a TSMC digital 90-nm CMOS technology. Both chips were tested on board using chip-on-board packages with ESD diodes added at the inputs and outputs. LNA1 achieves a 3-dB bandwidth of 9 GHz with 10 dB of power gain and a minimum noise figure (NF) of 4.2 dB. LNA2 achieves a 3-dB bandwidth of 3.2 GHz with 15.5 dB of power gain and a minimum NF of 1.76 dB. The two LNAs have third-order intermodulation intercept points of -8 and -9 dBm. Their power consumptions are 20 and 25 mW with a 1.2-V supply, respectively. Index Terms--CMOS, electrostatic devices (ESDs), low-noise amplifier (LNA), multiband receiver, resistive feedback, ultra-wideband (UWB).

In this paper, gain-enhancement techniques suitable for folded cascode low-noise amplifiers (LNAs) at low-voltage operations are presented. By employing a forward bias and a capacitive divider at the body of the MOSFETs, the LNA circuit can operate at a reduced supply voltage while maintaining an enhanced gain due to suppression of the negative impact of the body transconductance. In addition, a [G.sub.m]-boosting stage is introduced to further increase the LNA gain at the cost of circuit linearity. Using a standard 0.18-[micro]m CMOS process, two folded cascode LNAs are demonstrated at the 5-GHz band based on the proposed topologies. Consuming a dc power of 1.08 mW from a 0.6-V supply voltage, the LNA with the forward-body-bias technique demonstrates a gain of 10.0 dB and a noise figure of 3.37 dB. The measured [P.sub.in-1 dB] and [IIP.sub.3] are -18 and -8.6 dBm, respectively. For the LNA with a [G.sub.m]-boosting feedback, a remarkable gain of 14.1 dB gain is achieved with a dc power of 1.68 mW. Index Terms--Body transconductance, folded cascode, forward body bias, [G.sub.m] boosting, low-noise amplifiers (LNAs), low power, low voltage.

Exact and simple expressions have been obtained for the intrinsic noise figure of monolithic microwave integrated circuit distributed amplifiers (DAs). The method has been applied on both MESFET and HBT DAs. It has been shown that the complexity of the obtained formulas is much less than that of the previously published literature. The results of the new theory are then compared with that of the previous theories and it has been shown that the results exactly match. Index Terms--Distributed amplifiers (DAs), HBT, intrinsic noise figure, MESFET, preamplifier.

As one of the potential high-power microwave devices on the level of gigawatts, relativistic klystron amplifier (RKA) can be used for power combination to further improve the radiation microwave power. Because of self-excited oscillation of the intense relativistic electron beam, the frequency and phase characteristics of general relativistic klystron devices are independent with the driven microwave pulse. In order to obtain frequency and phase locking, a method of improving the input power is put forward to inhibit these parasitic oscillations. This paper reports a particle-in-cell simulation study of the RKA's characteristics under the condition of strong power feeding. By making use of the 500-keV 6-kA electron beam, the simulation results show that strong input power can inhibit the parasitical oscillations in cavity and modulate the beam very well with only one cavity. About 5.4-kA modulation current and a microwave with power of 1.4 GW, bandwidth of 5%, and efficiency of 50% are obtained. The new amplifier driven by the strong input power proves to be a potential device to attain high amplitude stability, high efficiency, high spectral purity, wide bandwidth, and low level of phase and amplitude noise. Index Terms--High-power microwave (HPM), particle-in-cell (PIC) simulation, phase locking, relativistic klystron.

This paper describes the observation of pulse shortening in an 11.4-GHz magnicon amplifier due to competition with a parasitic gyrotron mode. This effect was observed following the installation of a new electron beam collector. The parasitic mode occurred only at high operating powers, when the beam transverse momentum was high, and the growth of the parasitic mode caused the power in the output pulse to drop substantially. We analyze the competition between the gyrotron and magnicon modes in the output cavity using a time-dependent multimode gyrotron simulation code that has been specially modified to model competition between synchronous magnicon and nonsynchronous gyrotron interactions, and compare the results to experimental observations. We also analyze the effect due to the change in the collector. Index Terms--Electron devices, gyrotron, magnicon, microwave amplifier, parasitic mode.

The bandwidth potential of cascode HBT-based broadband amplifiers following the traveling-wave amplifier (TWA) concept is studied. An approximate expression for the gain of the circuit is derived, which is based on the transistor small-signal model and the artificial transmission-line parameters. In this way, a relation between the HBT cutoff frequencies [f.sub.T] and [f.sub.max] and the 3-dB cutoff frequency [f.sub.c] of the amplifier is obtained. This is very useful for assessing the gain-bandwidth potential of a given HBT technology for cascode-based TWAs. Applying these results, we study the potential of two technologies with different [f.sub.max]/[f.sub.T] ratios, an InP technology with [f.sub.max]/[f.sub.T] of 120 GHz/190 GHz, and a GaAs technology with [f.sub.max]/[f.sub.T] of 170 GHz/36 GHz. The higher influence of [f.sub.max] (compared to [f.sub.T]) on [f.sub.c] is quantitatively demonstrated. TWAs in both technologies were realized and measured, and good agreement between measurement and theory is obtained. Index Terms--Distributed amplifiers, equivalent circuits, [f.sub.max], [f.sub.T], GaAs, HBT, InP, integrated circuit modeling, semiconductor device modeling.

Highly efficient multiband power amplifiers (PAs) are key elements for the development of future multistandard multiband communication terminals and cognitive radios. This paper reports the design of a multiharmonic dual-band Class-F power amplifier for applications at wireless communication frequencies based on a switchless multiharmonic multiband load coupling network topology. The proposed output network topology is able to precisely synthesize Class-F impedance conditions with up to three harmonics at two distinct nonharmonic frequencies without the need of switches or electronically tunable elements. The proposed topology was used to design a Class-F PA in hybrid technology for the frequency bands at 1.7 and 2.14 GHz. Optimum impedances for maximum efficiency of the used GaAs MESFET for the two bands were determined by multiharmonic load-pull measurements and synthesized by the proposed switchless dual-band Class-F network. With a dual-band input matching network, the fabricated PA achieves 44.0 % and 61.3 % drain efficiency for an output power of more than 32.8 dbm and 34.4 dbm at 1.7 and 2.14 GHz, respectively. To the best knowledge of the authors, this is the first concurrent multiharmonic dual-band PA reported in open literature. Index Terms--Class F, cognitive radio, dual-band power amplifiers, GaAs MESFETs, high efficiency, microwave amplifiers.

This paper presents designs and measurements of distributed amplifiers (DAs) processed on a 130-nm silicon-on-insulator CMOS technology on either standard-resistivity (10 [ohm] * cm) or high-resistivity (>1 k[ohm] * cm) substrates, and with either body-contacted (BC) or floating-body (FB) MOSFETs. Investigations have been carried out to assess the impact of active device performance and transmission line losses on circuit design by means of simulations, analytical calculations, and comparisons of the small-signal equivalent-circuit parameters. On standard-resistivity substrates, DAs with FB devices and lossy microstrip lines on thin film exhibit a measured gain of 7.1 dB and a unity-gain bandwidth (UGB) of 27 GHz for a dc power consumption of 57 mW. With the introduction of high-resistivity substrates, other DAs, with the same architecture and using lower loss coplanar waveguide lines, show a UGB of 51 GHz with FB devices and 47 GHz with BC devices. To the authors' knowledge, the designs presented in this paper achieve the best tradeoffs in terms of gain, bandwidth, and power consumption for CMOS-based circuits with comparable architecture. Index Terms--CMOS, coplanar waveguides (CPWs), distributed amplifier (DA), microstrip (MS), monolithic microwave integrated circuit (MMIC), silicon-on-insulator (SOI).

A fully integrated balanced amplifier was realized in a standard 0.18-[micro]m CMOS technology. From the measured S-parameters, a gain up to 21.5 dB was achieved at 45.4 GHz under a supply voltage of only 1 V and a total power consumption of 89 mW. An effective technique, i.e., [pi]-type parallel resonance, was proposed to enhance the device and circuit frequency response. In addition, the semicoaxial line structure was used to reduce the signal loss and physical size of the Lange couplers in the amplifier. To the best of the authors' knowledge, the proposed balanced amplifier demonstrated the highest operation frequency and the lowest operation voltage among the published millimeter-wave amplifiers using a similar technology. Index Terms--Balanced amplifier, CMOS, Lange coupler, millimeter wave, parallel resonance, semicoaxial line.

This paper reviews and analyzes a fully integrated electrostatic discharge (ESD)-protected low-noise amplifier (LNA) for low-power and narrowband applications using a cascode inductive source degeneration topology, designed and fabricated in 130-nm CMOS silicon-on-insulator technology. The designed LNA shows 13-dB power gain at 2.4 GHz with a noise figure of 3.6 dB and input return loss of -13 dB for power consumption of 6.5 mW. An on-chip 'plug-and-play' ESD protection strategy based on diodes and a power clamp is used at the input and output of the LNA, and has an ESD protection level up to 0.8-, 0.9-, and 1.4-A transmission line pulse current. This corresponds to 1.2-, 1.4-, and 2-kV human body model stress applied at, respectively, the RF input, RF output, and [V.sub.DD] bus. Measurement shows a minor RF performance degradation by adding the protection diodes. Index Terms--CMOS, electrostatic discharges (ESDs), low-noise amplifier (LNA), narrowband, partially depleted (PD) silicon-oninsulator (SOI), RF, transmission line pulse (TLP).

This paper describes a method for designing cryogenic silicon--germanium (SiGe) transistor low-noise amplifiers and reports record microwave noise temperature, i.e., 2 K, measured at the module connector interface with a 50-[OMEGA] generator. A theory for the relevant noise sources in the transistor is derived from first principles to give the minimum possible noise temperature and optimum generator impedance in terms of dc measured current gain and transconductance. These measured dc quantities are then reported for an IBM SiGe BiCMOS-8HP transistor at temperatures from 295 to 15 K. The measured and modeled noise and gain for both a single- and two-transistor cascode amplifier in the 0.2-3-GHz range are then presented. The noise model is then combined with the transistor equivalent-circuit elements in a circuit simulator and the noise in the frequency range up to 20 GHz is compared with that of a typical InP HEMT. Index Terms--Cascode, cryogenic, low-noise amplifier (LNA), noise parameters, silicon--germanium (SiGe).

Traditional simulation approaches for predicting the frequency-domain response of nonlinear devices to multiple tone excitation enforce correlation of the phases of the individual tones. This is the case with time-domain simulators and transform-based schemes such as Harmonic balance as the waveform must be single valued, thus enforcing correlation. Previous efforts in frequency-domain simulators using the arithmetic operator method (AOM) also produced results in good agreement with measurements for correlated-phase input signals. Here, the AOM is applied to directly determine the spectral response of nonlinear systems to excitation by multiple uncorrelated tones in a single simulation. Verification is provided using measurements of a nonlinear amplifier excited by 15 independent tones and comparison to the average of the ensemble of results from multiple correlated-phase simulations. Index Terms--Arithmetic operator method (AOM), computer-aided analysis, multitone signals, nonlinear amplifiers, uncorrelated phase.

This paper presents an inductorless low-noise amplifier (LNA) design for an ultra-wideband (UWB) receiver front-end. A current-reuse gain-enhanced noise canceling architecture is proposed, and the properties and limitations of the gain-enhancement stage are discussed. Capacitive peaking is employed to improve the gain flatness and --3-dB bandwidth, at the cost of absolute gain value. The LNA circuit is fabricated in a 0.13-[micro]m triple-well CMOS technology. Measurement result shows that a small-signal gain of 11 dB and a --3-dB bandwidth of 2-9.6 GHz are obtained. Over the -3-dB bandwidth, the input return loss is less than -8.3 dB, and the noise figure is 3.6-4.8 dB. The LNA consumes 19 mW from a low supply voltage of 1.5 V. It is shown that the LNA designed without on-chip inductors achieves comparable performances with inductor-based designs. The silicon area is reduced significantly in the inductorless design, the LNA core occupies only 0.05 [mm.sup.2], which is among the smallest reported designs. Index Terms--CMOS integrated circuits, current reuse, gain enhancement, low-noise amplifier (LNA), noise cancellation, RF integrated circuit (RFIC), ultra-wideband (UWB).

The article presents a seven-beam electrostatically focused klystron with planned output of 2 kW at frequency 5.8 GHz. Findings reveal the suitability of the klystron as a source for microwave plasma production in a gridded ion thruster.

The noise penalty (NP) metric is useful in long-haul analog link design, as it predicts degradation of the RF noise figure (NF), 1-dB compression dynamic range (CDR), and the spurious-free dynamic range (SFDR) for a single-amplifier link. We extend the NP theory to predict the cascaded NP of a multiamplifier fiber-optic link from the NP due to each of the individual amplifiers. A cascaded NP expression is derived and compared to experimental results from a 60-km link consisting of three amplifiers. The measured NP of 11.8 dB for the link matches well with our theoretical prediction. The link gain of -7 dB, RF NF of 31 dB, 1-dB CDR of 148 dB. Hz, and of 108 dB. [Hz.sup.2/3] are also measured and matched to predicted values for the measured NP. Index Terms--Analog photonics, intensity modulation direct detection, microwave photonics, noise penalty (NP) of erbium-doped fiber amplifier (EDFA).

A wireless radio transmitter with an integrated variable-impedance antenna is demonstrated. The transmit signal is connected via a switch to the antenna at one of several feed points that correspond to different load impedances that are optimal for the power amplifier at different transmit power levels. It is shown that this can be used to improve the efficiency of the transmission at low and medium transmit powers. The variable antenna load is demonstrated with a planar inverted-F antenna, but the method can be applied to any antenna with suitable impedances. Index Terms--Antennas, impedance matching, microwave communication, power amplifiers (PAs).

The latest model Ka-band helix traveling wave tube (TWT) amplifier, which is designed and manufactured onboard space satellite-communication systems at L-3 Communications Electronics Technologies, Inc., has shown over 250-W RF output power. The model 999HA can be mated to either 7-kV electronic power conditioners (EPCs) for low-power applications or to the 14-kV EPC (model 1693HC) to support higher power applications.

Large signal code is used to study the traveling-wave tubes (TWTs) and its results are compared with that of a transverse TWT of the same dc beam power. The results have shown that the transverse TWT retains its advantages under large signal conditions.

A comparison of envelope elimination and restoration (EER) and envelope tracking (ET) is discussed and a 'hybrid' wideband EER power amplifier (PA) for the WLAN 802.11g system is proposed. A 60% efficiency (the output envelope signal power/input dc power) DC-20-MHz wideband envelope amplifier is designed for wideband EER and wideband ET (WBET) applications. A design method is developed to optimize the efficiency of the envelope amplifier for a given peak-to-average ratio and average slew rate of the envelope signal. An experimental 'hybrid' Class-E EER system shows an overall efficiency (modulated RF output power/envelope amplifier dc input power) of 36% and power-added efficiency (the modulated RF output power/envelope amplifier dc input power plus RF input power) of 28% for a WLAN 802.11g signal at 19-dBm (80 mW) output power at 2.4 GHz. Digital predistortion, time alignment, and memory effect mitigation are implemented. The measured 3% error vector magnitude exceeds the 802.11g specification for 5% for a 54-Mb/s modulation signal. Index Terms--Class E, dc-dc converter, delta-modulation (DM), digital predistortion, envelope elimination and restoration (EER), envelope tracking (ET), hysteresis control, memory effect, modulator, orthogonal frequency-division multiplexing (OFDM), polar transmitter, power amplifiers (PAs), power tracking, pulse-width modulation (PWM), time alignment, wireless local area network (WLAN).

This paper presents the practical design methodology of an InP high electron-mobility transistor broadband low-noise amplifier (LNA) using multilayer transmission lines. The LNA consists of high-pass reactive matching circuits and resistive-feedback circuits in order to achieve both low-noise and broadband characteristics. The fabricated five-stage LNA successfully delivered a 43-dB gain with a noise figure of 1.9 dB at 23 GHz, and a gain of more than 40 dB from 18 to 43 GHz. The maximum gain was 49.5 dB at 32 GHz and the chip size was only 1.8 x 0.9 m[m.sup.2], resulting in a gain density of 30.5 dB/m[m.sup.2]. To the best of our knowledge, this gain density is the highest performance in any K a-band LNA reported to date. In addition, a more compact LNA using spiral inductors was also demonstrated. Index Terms--Gain density, InP high electron-mobility transistor (HEMT), low-noise amplifier (LNA), multilayer.

The base-region optimization of SiGe power heterojunction bipolar transistors (HBTs) for high-frequency microwave power amplification is investigated. It is observed that employing a heavily doped base region in conjunction with a high Ge content of proper profile can effectively improve the large-signal power-gain values of SiGe HBTs while maintaining their high breakdown voltages, and thus allow them to be efficiently operated with high power at higher microwave frequencies.

The dual functions of the rectangular hollow dielectric resonator antenna (DRA) as an antenna and a packaging cover are investigated. The design methodology is discussed, and the return loss, impedance, and radiation patterns for the fundamental mode are presented at 2.4 GHz, a popular frequency band for the WLAN and wireless communications. A low-noise amplifier is integrated successfully into the embedded cavity to form an active DRA, and the amplified radiation patterns are analyzed. The proposed DRA provides a possible solution to the size minimization of transceivers. Index Terms--Active antennas, aperture antennas, dielectric resonator antennas (DRAs), microwave amplifiers, resonance.

The quantification of the effect of higher-order radial space charge modes on the evolution of beam harmonic current is discussed. Higher-order radial space-charge modes are able to change both the shape of the harmonic current evolution and its magnitude particularly after reaching the peak harmonic current.

The frequency dependences of thermal noise at the output of superconducting filters with Butterworth and quasi-elliptic transfer characteristic and 50-ohm source and load resistances were investigated. Satellite thermal noise can be avoided simply in placing the LNA in front and the superconducting filter behind at the output of the receiver.

We have developed a 27- and 40-GHz tuned amplifier and a 52.5-GHz voltage-controlled oscillator using 0.18-[micro]m CMOS. The line-reflect-line calibrations with a microstrip-line structure, consisting of metall and metal6, was quite effective to extract the accurate S-parameters for the intrinsic transistor on an Si substrate and realized the precise design. Using this technique, we obtained a 17-dB gain and 14-dBm output power at 27 GHz for the tuned amplifier. We also obtained a 7-dB gain and a 10.4-dBm output power with a good input and output return loss at 40 GHz. Additionally, we obtained an oscillation frequency of 52.5 GHz with phase noise of -86 dBc/Hz at a 1-MHz offset. These results indicate that our proposed technique is suitable for CMOS millimeter-wave design. Index Terms--Millimeter wave, phase noise, tuned amplifier, voltage-controlled oscillator (VCO).

A method for designing multistage broad-band amplifiers based upon well-known filter synthesis techniques is presented. Common all-pole low-pass approximations are used to synthesize prototype amplifier circuits that may be scaled in frequency and impedance. All-pass filters introduced at the first stage are shown to improve input match while maintaining circuit performance less 6 dB gain. A theoretical comparison is made with the distributed amplifier and the cascaded single-stage distributed amplifier. Theoretically, a larger gain-bandwidth product is achieved using the synthesis technique. A proof-of-concept Butterworth low-pass two-stage amplifier was designed, simulated, and measured and achieved a flat gain performance of 1-4 GHz with a power gain of 14.54 [+ or -] 1 dB close to the predicted 1-4.2 GHz, 154 [+ or -] 1 dB. Index Terms--Active filters, all-pass circuits, broad-band amplifiers, Butterworth filters, microwave circuits, microwave FET amplifiers.

A monolithic-microwave integrated-circuit (MMIC)-compatible miniaturized 'active' predistorter using cascode FET structures is presented. The predistorter has added functionality of gain, as well as programmable gain and phase variation characteristics, which are required to compensate for the nonlinear distortion of a wide range of power amplifiers (PAs). Thanks to the inherent gain of the predistorter, a need for an additional buffer amplifier is eliminated. Furthermore, it can eventually replace the first-stage amplifier in the multistage PAs, making this approach well suited to MMIC implementation. A simple analysis is performed to understand the phase variation mechanisms in the proposed predistorter and to identify the dominant sources of phase variation. From the analysis, the origins of nonlinear distortion of predistorter were found to be [G.sub.m] of the upper FET and [R.sub.ds] of the lower FET. It was also found from the analysis that the gain and phase variation can be programmed by controlling the bias and size of the transistors. To demonstrate the general usefulness of this predistorter, the cascode predistorter was applied to linearize watt-level MMIC amplifiers for code-division multiple-access handset applications, as well as 30-W high power amplifiers (HPAs) for base-station applications. Adjacent channel power ratio (ACPR) improvement of 3-5 dB was achieved with off-chip predistorter when applied to 0.9-W monolithic amplifiers. The predistorter was also integrated with a 1.6-W MMIC PA on a single chip, replacing the first-stage transistor of the amplifier. An integrated predistorter showed ACPR improvement of 2.5 dB at 28-dBm output power. When applied to a base-station HPA, the spectral regrowth is suppressed by approximately 10 dB at the average output power of 44.7 dBm. The 'active' predistorter of this study can be a viable general-purpose linearization technique that can be applied to a wide range of amplifiers. Index Terms--Distortion, linearization, monolithic microwave integrated circuit (MMIC), nonlinear, power amplifier (PA), predistorter.

This paper proposes a new technique for reducing the intermodulation (IM) distortion products in a high-power amplifier (HPA) array. The proposed technique dissolves the relations between carriers and IMs by applying IM phase control. As a result, IMs are distributed to all the output ports in the array, and the carrier power to intermodulation power ratio (C/IM) of the HPA array can be increased. The improvement in C/IM is as high as 10 log N dB, where N is the number of HPAs. Newly developed even-order distortion implemented intermodulation distortion controllers (EODICs) are used to achieve the IM phase control. A test carried out using a four-parallel HPA array with EODICs confirms that the technique noticeably improves C/IM and demonstrates its validity. Index Terms--Intermodulation (IM) distortion, monolithic microwave integrated circuits (MMICs), power amplifiers, satellite communication onboard systems.

The gyro-traveling wave-tube (gyro-TWT) is a microwave amplifier with simultaneous high power, high frequency and broad bandwidth capabilities. The design technique associated with the ceramic loading scheme using the 35 GHz gyro-TWT is described.

The generation of RF/microwave power is required not only in wireless communications, but also in applications such as jamming, imaging, RF heating, and miniature dc/dc converters. Each application has its own unique requirements for frequency, bandwidth, load, power, efficiency, linearity, and cost. RF power is generated by a wide variety of techniques, implementations, and active devices. Power amplifiers are incorporated into transmitters in a similarly wide variety of architectures, including linear, Kahn, envelope tracking, outphasing, and Doherty. Linearity can be improved through techniques such as feedback, feedforward, and predistortion. Index Terms--Amplifier, Chireix, class A, class B, class C, class D, class E, class F, Doherty, envelope tracking, feedback, feed-forward, HF, Kahn, microwave, outphasing, power, predistortion, transmitter, UHF, VHF.

The results of two techniques for optical carrier regeneration and wavelength reuse using semiconductor optical amplifiers (SOAs) are presented in this paper. The main objective is to recover an optical carrier by erasing its amplitude modulation. The first technique employs gain compression of deeply saturated SOAs. The second technique uses a feed-forward approach, where a delayed current signal is injected into the SOA with the same shape of the incoming optical pulse. The second technique could be capable to recover the optical carrier with less than 3-dB noise. However, it was observed that the SOA gain recovery time limits the maximum usable bit rate. Theoretical simulation showed good agreement with experimental results. Index Terms--Optical carrier regeneration, optical pulse reshaping, optical wavelength reuse, semiconductor optical amplifier.

Heterojunction FETs or high electron-mobility transistors (HEMTs) based on [Al.sub.x] [Ga.sub.1-x] N/GaN are studied for their use as control components for high-power microwave and RF control devices (switches, phase-shifters, etc.). A linear operation model was developed for these components so that optimum transistor geometry and operation parameters may be determined for their use in control applications. The model was verified with experimental data taken on test HEMT devices. It was experimentally established that the HEMT resistance is low for voltages of + 1.0 V, and that the capacitive reactance increases for dc gate voltages below the threshold voltage of approximately -1.5 V. Index Terms--Gallium nitride, high electron-mobility transistors, microwave control.

The need for both linear and efficient pseudomorphic high electron-mobility transistors (pHEMTs) for modern wireless handsets necessitates a thorough understanding of the origins of intermodulation distortion at the device level. For the first time, the dynamic large-signal internal physical behavior of a pHEMT is examined using a quasi-two-dimensional physical device model. The model accounts fully for device-circuit interaction and is validated experimentally for a two-tone experiment around 5 GHz. Index Terms--Intermodulation distortion, linearity, microwave power FET amplifiers, MODFET power amplifiers, MODFETs, semiconductor device modeling.

We derive a simple formula for the change in output when a device falls in a power-combining structure with identical matched devices. The loss is written in terms of the scattering coefficient of the failed device and reflection coefficient of an input port in the combining network. We apply this formula to several power combiners, including arrays in free space and enclosed waveguide structures. Our simulations indicate the output power degrades gracefully as devices fail, which is in agreement with previously published results. Index Terms - Graceful degradation, grid arrays, power combining, quasi-optics.

This paper presents a broad-band spatial power-combining system based on tapered-slot antenna arrays integrated in a standard WR-90 waveguide environment. The system is designed using a modular tray architecture, providing full waveguide-band frequency coverage and an excellent thermal environment for a set of monolithic-microwave integrated-circuit (MMIC) amplifiers. The shape of the tapered-slot or finline structures was optimized to minimize return loss and provide a broad-band impedance transformation from the waveguide mode to the MMIC amplifiers. A prototype eight-element array using commercial GaAs MMIC power amplifiers yielded a maximum of 41-W output power (continuous wave) with a gain variation less than [+ or -] 1.2 dB within the entire band of interest. The average combining efficiency over the operating band was estimated at 73%. The results suggest the efficacy of the design and a strong potential for higher powers by moving toward a greater number of MMIC's per tray and a larger number of trays. Should the 100-W system be realized in the near future, our combiner system will become a promising candidate to challenge the dominant position currently claimed by the traveling-wave tube amplifiers. Index Terms - Finline structure, power combining, spatial power combiner.

Constant equivalent noise resistance [R.sub.n] circles of a series-feedback amplifier are presented. They visualize on the series-feedback element plane, which is the region where a series feedback can be selected in order to decrease the value of [R.sub.n]. The [R.sub.n] circles demonstrate that lossy series-feedback impedances can lower the equivalent noise resistance. This is an important point because it demonstrates that the feedback element can make the noise figure less sensitive to changes in the input mismatch; and careful selection of the feedback element may reduce the noise figure of the device, despite the loss in the feedback branch. The use of [R.sub.n] circles along with circles for a constant magnitude of scattering parameter [S.sub.ij] on the feedback plane is explained. Index Terms - Amplifier noise, circuit noise, feedback amplifiers, feedback circuits, microwave amplifiers, noise.

The design, fabrication, and performance of producible, high-performance K- and [K.sub.a]-band pHEMT low-noise MMIC amplifiers using the embedded transmission line (ETL) circuit concept with top-side grounding are reported. A state-of-the-art noise figure of 1.2 dB with 25-dB gain is achieved at 31 GHz. These amplifiers can be implemented in low-cost, ultra-compact receiver modules for emerging spaceborne phased-array communication applications. Index Terms - MMIC amplifiers, MMIC receivers, MMIC's, MODFET amplifiers.