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This paper describes a design study and experimental demonstration on a cavity-type power combiner producing 80 kW at 464 MHz. The power combiner consists of (1) a 40-way equal phase/amplitude power divider, (2) a cavity-type power combiner, and (3) 40 LDMOS power amplifier modules. The power divider produces equal power and phase through a Ill-way radial power divider and 3-dB Wilkinson dividers. The power combiner is a cylindrical cavity resonating at TM010 mode with 40 input ports. The combined power is extracted through 6-1/8' coaxial transmission line. Measured results of the 40-way power combiner show an output power of 80 kW and combining efficiency of $> 95{\%}$ , which is in a good agreement with HFSS simulation results.

In this paper, we present design and measurement of LNA(Low Noise Amplifier) based on GaN HEMT(Gallium Nitride High Electron Mobility Transistor) to reduce the total noise figure of radar receiver and for robustness of LNA. In radar receiver using LNA based on GaAs(Gallium Arsenide) technology, limiter is necessary at the very front of the radar receiver to protect LNA. As a result, total noise figure of radar receiver is deteriorated. In this research, measured noise figure of LNA based on GaN HEMT is below 2 dB. In the case of commercialized GaAs LNA, recommended maximum input power is about 30 dBm. On the other hand, GaN HEMT LNA which is designed and measured is burned-out when input power is 43 dBm and robustness is guaranteed at input power 45.4 dBm. Key words: LNA, GaN HEMT, Robustness, Current Limit ‡wx ˆ3‰Š 5wx‹9Œ wx . Ž ‘+C’“(Department of Wireless Communications Engineering,, Kwangwoon University) *ˆ3‰Š(Samsung Thales, Co, Ltd) `Manuscript received December 24, 2014 ; Revised February 5, 2015 ; Accepted February 6, 2015. (ID No. 20141224-105)`Corresponding Author: Jin-Joo Choi (e-mail: jinchoi@kw.ac.kr)

This paper presents a design and fabrication of Ku-band power amplifier using Gallium Nitride High Electron Mobility Transistor (GaN HEMT) die. In order to fabricate the low-cost Ku-band power amplifier, a Printed Circuit Board(PCB) was used for input/output matching circuits instead of manufacturing process to use an expensive substrate. The measured output power is 42.6 dBm, the drain efficiency is 37.7 % and the linear gain is 7.9 dB under pulse operation at the frequency of 14.8 GHz. Under the continuous wave(CW) test, the output power is 39.8 dBm, the drain efficiency is 24.1 % and the linear gain is 7.2 dB.Key words: Ku-Band, GaN HEMT Die, Low-Cost, Power Amplifier LMN62013OPQRSA8MN#(TU$%MNVIW.X YZ [\]^[ (Department of Wireless Communications Engineering, Kwangwoon University) *QRSA8(Samsung Thales) Manuscript received February 4, 2014 ; Revised March 11, 2014 ; Accepted April 16, 2014. (ID No. 20140204-016)Corresponding Author: Jin-Joo Choi (e-mail: jinchoi@kw.ac.kr)

A new class of compact and lightweight S-band 1 kW traveling-wave tube (TWT) is being developed for a microwave power module (MPM) that will be used for phased antenna array radar applications. The proposed S-band MPM provides a tenfold peak power increase compared to state-of-the-art S-band MPMs. In this paper, the design of the vacuum power booster TWT part of the MPM is presented. The compact and lightweight S-band TWT is driven by a 6 kV, 0.9 A electron beam. The amplifier is predicted by large-signal simulations to generate over 1 kW at S-band with 25 dB saturated gain and over 40% efficiency. The stability from unwanted oscillations has been investigated. To suppress the oscillations, the helix circuit has been coated with carbon composite material. The coaxial input and output antennas have been fabricated. For efficiency enhancement, a multi-stage depressed collector (MDC) has been designed using a 3D particle-in-cell (PIC) simulator, VORPAL. The collector design makes use of a current loop based on a feedback mechanism for effective design process. The integrated designs of a helix circuit, an electron gun, a periodic permanent magnet (PPM), antennas, and a collector are presented.

In this article, a frequency-tunable 150W harmonic-tuned power oscillator is presented. The harmonic-tuned power amplifier of the oscillator was designed for improving drain efficiency with a single laterally diffused metal oxide semiconductor transistor using a nonlinear harmonic balance simulation code. The oscillation frequency was tuned by a mechanical phase shifter in the delay-line feedback loop circuit. Experimental results show that the output power and the drain efficiency of the oscillator were almost same as in the power amplifier with the same transistor and operating in the same frequency range. The measured output power and drain efficiency of the fabricated oscillator were 51.8 ± 0.6 dBm and better than 55.9%, respectively, across the 902–928 MHz band. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1459–1462, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25970

We present simulation results on wideband millimeter wave amplification on a coupled-cavity traveling-wave-tube driven by an ultra short impulse signal. The impulse signal of pulse width of 1 nsec modulated with a carrier frequency of 29.1 GHz is injected into the amplifier. The resulting output spectra were found to be wideband with a 2.4% fractional bandwidth at a center frequency of 29.1 GHz, where peak output power of 658 W remained same as that obtained at CW operation with a single drive frequency of 29.1 GHz.

In this paper, a simple and effective active load-pull method is proposed, and the method to improve the efficiency of X-band power amplifier using harmonic control circuit is presented. The proposed active load-pull system mainly consists of directional coupler, phase shifter, short circuit, and power amplifier, and allows a user to access reflection coefficients near the edge of the Smith chart( Γ 1) easily. The device used in this paper is Mitsubishi's GaAs FET MGF1801, and the operating frequency of the power amplifier is 9 GHz, The amplifier had output power of 21.65 dBm and drain efficiency of 24.9 % at class-A, and had output power of 21.46 dBm and drain efficiency of 53.3 % at class-AB. Harmonic control circuit is designed only second and third harmonic components because of the bandwidth limitation of the microwave components. The drain efficiency is improved as much as 6.4 % compared with class-AB power amplifier. Key words : Active Load-Pull, Harmonic Load-Pull, High Efficiency, Switching-Mode Amplifier

In this article, a compact dual-mode λg/2 bandpass filter with the characteristic of harmonic rejection is designed and implemented.The second and third harmonics of the suggested bandpass filter are rejected by using the additional open stubs of the T-type equivalent circuit for the quarter wavelength line. Also, the J-inverter is investigated as functions of the impedance and electrical length of the open stub of dual-mode λg/2 resonator. From the results, the lower impedance of open stub of dual-mode λg/2 resonator is better for the good performance of the dual-mode λg/2 bandpass filter. The harmonic-rejected dual-mode λg/2 bandpass filter shows the characteristic of suppression of harmonics until 8 GHz and the insertion and return losses of 0.96 and 18.89 dB, respectively, at the center frequency of 2.43 GHz. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2288–2291, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25457

A three-dimensional particle-in-cell (PIC) code, MAGIC3D, is used to simulate an A6 relativistic magnetron with metal tuner. As inserting six conducting rods into the resonators in regions where the RF magnetic field is high, the resonant frequency of 2pi-mode (n=6) of the A6 magnetron is tuned over the range from 4.27 to 4.47 GHz. The simulations show that with perturbed RF magnetic fields caused by metal tuner, the performance of the A6 magnetron in terms of radiation output power, frequency spectrum, and efficiency is superior compared with those using the uniform RF magnetic fields. Maximum output power of A6 with three tuners is 600 MW at 4.4 GHz, corresponding to a magnetron efficiency of 7.2%, which is about 20% higher than the conventional A6 magnetron where the axial external magnetic field is 5.5 kG and the beam voltage and the total current are 360 kV and 23 kA, respectively. When the tuner position of three metal rods is 8 cm, which is adjusted to get maximum power, a spectral amplitude in the pi-mode is lower 33 dB in power than the 2pi-mode.

In this letter, a novel design method of tapped-line gap-coupled half-wavelength band-pass filter (BPF) using J- or K-inverter is proposed. A model of tapped-line is composed of shunt stub and the additional transmission line that has the electrical length of the negative value. The electrical lengths of the stub and line are functions of the line's impedance and the inverter that has a variable of filter's bandwidth. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1253–1256, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22417

This paper presents results of computational and experimental studies of carbon nanotube (CNT) cathodes in gridded focusing guns intended for traveling-wave tube applications. With a curved CNT cathode, a cold beam emission of 11 mA was observed in a diode configuration. Two gridded focusing cathodes pasted with CNTs were then fabricated. When the applied cathode voltage was -0.86 kV, both grid and anode were at ground potential, and the cathode-to-grid distance was 200 mum, the dc emission current from the first gridded CNT cathode was measured to be 4.2 mA. The triode field emission characteristics with two accelerating stages in pulse operation were also examined. With the cathode voltage at -4 kV, a cathode-grid potential difference of 1.38 kV, and a pulsewidth of 20 mus, the measured pulsed current emission was 4.6 mA. The measured current was found to agree with MAGIC2D simulation results. Furthermore, by configuring a double-gridded focusing gun, a significant improvement in the beam focusing data collected through computer modeling was seen

In this paper, we fabricate RF integrated passive devices (RFIPDs) on two types of substrate. One is smart silicon substrate with a 25-μm-thick SiO2 surface, and the other is glass substrate. A low-cost manufacturing technology, BCB interlayer, and 10-μm Cu plating process are used to implement high-performance RFIPDs. We investigate the power-handling performance with these two types of RFIPDs. Generally, RFIPDs are used for RF front-end module components, so handling power is very important factor. But, these two types of RFIPDs show different handling-power performances. In contrast to the 5.5-W power handling of the LPF on smart silicon substrate, that of the LPF on glass substrate is below 1.5 W (with CW power and 168 h operating time). © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 441–444, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20848

In this article, a drain-source voltage and current waveforms measurement method for a fabricated power amplifier is presented. Harmonic components of the drain-source voltage and the current were obtained using measured output voltage and harmonic ABCD matrices of a load matching network. The drain-source voltage and current waveforms of a fabricated power amplifier that is operated nonlinearly were successively measured using the proposed measurement method without any influence in the power amplifier operation. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2335–2337, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27100

A high-power rising-sun magnetron oscillator (AX-9) operating at 9.50 GHz is examined by the use of a three-dimensional particle-in-cell (PIC) code, MAGIC3D. A mode spectrum of the 18 vanes rising-sun magnetron cavity is obtained from both an analytic field theory and the numerical code MAGIC3D. A large mode separation in the vicinity of a /spl pi/-mode is observed in the rising-sun configuration. A time evolved electron flow exhibits nine space charge spokes in the PIC simulations, which confirms the /spl pi/-mode oscillation in the 18 vanes rising-sun magnetron. When space charge spokes build up in the interaction region, a single frequency RF oscillation starts to grow and the leakage current escaping from the interaction region reduces to zero. Simulations predict that the saturated radiation power measured at the output waveguide is 250 kW at 9.50 GHz, corresponding to a magnetron efficiency of 53% where the external magnetic field is 0.52 T and the beam voltage and current are 28 kV and 17 A, respectively.

A highly reproducible, low-cost folded waveguide traveling-wave-tube amplifier is designed using the Pierce theory and a three-dimensional (3-D) particle-in-cell (PIC) code. The amplifier is designed to operate at 40-48 GHz with peak output radiation power of 200 W. Initial circuit parameters are obtained from the Pierce theory and circuit dispersion relations. A nonlinear large-signal performance of the amplifier is predicted from 3-D PIC simulations. Simulations show that the amplifier produces a saturated radiation power of 200 W at 44 GHz, corresponding to 5.6% electronic efficiency where the beam voltage and current are 21 kV and 0.17 A, respectively. A saturated 3-dB bandwidth is found to be 16% (40.5-47.5 GHz).

The design and fabrication of a high-efficiency inverse class-F power amplifier using a 10-W gallium nitride (GaN) high-elec- tron mobility transistor at 1 GHz is presented. The output load network has been used to control harmonic components for high-efficiency oper- ation. The measurement results show that power-added efficiency of 74.2%, drain efficiency of 77.5%, and gain of 13.7 dB at an output power of 39.8 dBm for a continuous wave signal. © 2008 Wiley Period- icals, Inc. Microwave Opt Technol Lett 50: 2420 -2422, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ mop.23678

Summary form only given. A new class of microwave power module (MPM) is being developed for phased antenna array applications. The MPM consists of a compact S-band 1 kW traveling-wave tube (TWT), a solid-state pre-amplifier, and a power supply. The proposed S-band MPM provides tenfold peak power increase compared to state-of-the art S-band MPMs. The TWT amplifier is driven by a 6 kV, 0.9 A electron beam. A depressed collector which was designed by using a 3-D conformal finite-difference time-domain particle-in-cell code,VORPAL [1], was employed to maximize the efficiency. The compact and lightweight S-band TWT is short in length (circuit length is six inches) and weighs only 700 g. The preliminary hot test result of the TWT showed 900 W peak power in S-band. The design, fabrication, and characterization of each components that consist the MPM will be discussed. The cold and hot test results will be presented.

A compact S-band 1 kW traveling-wave tube (TWT) is being developed for microwave power module (MPM) phased antenna array radar applications. The Sband MPM provides tenfold peak power increase compared to the currently available ones. Circuit characteristics including interaction impedance, phase velocity, power, and gain of the TWT were predicted using large signal code. The test result of the compact Sband 1 kW TWT will be presented along with design the results for individual components that include the electron gun, antennas, window, and collector.

This paper proposes a new configuration for power oscillator based on the combined power amplifier. The focus is on power combining as a oscillator structure with a positive feedback loop line. The proposed configuration consists of a harmonic-tuned combined power amplifier using two Gallium Nitride High Electron Mobility Transistors (CGH40025), 3dB Wilkinson divider/combiner, a directional coupler, an isolator, a coaxial line and mechanical phase shifters. The steady state oscillation occurs in a delay line feedback loop which length is adjusted to a oscillation frequency. The measured output power and conversion efficiency of the proposed oscillator are 46.8 dBm and 58 %, respectively, at 2.45 GHz with a drain bias voltage of 28 V.

In this paper, a frequency tunable, high-efficiency power oscillator using Gallium Nitride High Electron Mobility Transistor (GaN HEMT) for the RF power source applications is designed and fabricated. The steady state oscillation occurs in a delay line feedback loop which length is adjusted to tune oscillation frequency. A harmonic-tuned matching network technique is employed to obtain high conversion efficiency characteristic of the oscillator. The measured output power and conversion efficiency of the fabricated oscillator are 44.63±0.2 dBm and better than 62%, respectively, across the 890–950 MHz band with a drain bias voltage of 40 V. Then a hair-pin resonator is designed and employed into the oscillator in order to improve phase noise characteristics and frequency selectivity. The experimental results of the oscillator with the hair-pin resonator exhibit the output power of 43.55 dBm, corresponding to the conversion efficiency of 61% at 920 MHz. The measured phase noise characteristics are −64 dBc/Hz and −81.24 dBc/Hz at 10 kHz offset without and with the hair-pin resonator, respectively.

A compact and lightweight S-band 1 kW traveling-wave tube (TWT) is being developed for microwave power module (MPM) radar applications. The S-band MPM provides a tenfold peak power increase compared to the currently available ones. Circuit characteristics including interaction impedance, phase velocity, power, and gain of the TWT were predicted using large signal code. Design of electron gun, periodic permanent magnet, and collector is complete. The helix circuit has been fabricated and is ready to be tested.

This paper describes the design and fabrication of a highly efficient switching-mode Class-E Doherty power amplifier using gallium nitride (GaN) high-electron mobility transistor (HEMT) for S-band radar applications. Measured results of the Doherty amplifier show power-added efficiency (PAE) and drain efficiency of 62.6% and 73.1% at 37 dBm of 6 dB output back-off point from saturated output power at 2.85 GHz, compared with PAE and drain efficiency of 42.9% and 44.7% for the case of balanced amplifier. It was found that PAE was improved by 19.7% by adopting the Doherty efficiency enhancement technique.

This paper presents a high-efficiency power oscillator, which uses LDMOS (Laterally Diffused Metal Oxide Semiconductor) transistor for high output power and a harmonic-tuned matching network to obtain high efficiency characteristic for RF power source application. A hair-pin resonator was designed and employed into the high efficiency power oscillator in order to improve phase noise characteristic and frequency selectivity. Measurement results show that output power of the power oscillator is 38.1 dBm, corresponding to a conversion efficiency of 73% at 981 MHz which is the highest efficiency reported in microwave power oscillator. Experiments performed with the hair-pin resonator show that output power is 36.9 dBm and conversion efficiency is 65%. Phase noises are measured to be 78.9 dBc/Hz and 103 dBc/Hz at 10 kHz offset without and with the hair-pin resonator, respectively.

In this paper, we have studied a high power oscillator of a high RF output power and a good phase noise. We designed the high power oscillator using LDMOS(laterally diffused metal oxide semiconductor) device by the use of an Agilent advanced design system (ADS). We also designed the rectangular cavity resonator in order to obtain a good phase noise by using a 3-D high frequency structure simulator (HFSS) code. In Section II, the simulation and measurement results of the planar cavity resonator (PCR) were described. In section III, the output characteristics of a high power oscillator using PCR was described.

This paper presents an inverse class-F power amplifier (PA) based on gallium nitride (GaN) high electron mobility transistor (HEMT) at 1 GHz. The implemented PA has a peak power-added-efficiency (PAE) of 74.1%, drain efficiency (DE) of 77.36%, and a gain of 13.76 dB at an output power of 39.58 dBm with a continuous wave operation at 28 volts. We have carried out the experiments with various pulsed operating conditions. A RF performance peak PAE of 74.28% with drain efficiency of 77.57% and a gain of 13.73 dB, at an output power of 39.66 dBm, was obtained at a pulse width of 100 mus with a duty of 10%. To evaluate the linearity of the inverse class-F amplifier, two-tone measurements have been tested. At a tone spacing of 100 kHz, the measured third-order intermodulation distortion (IMD3) was 13.2 dBc at peak PAE.

This paper focuses on PIC simulations of Ka-band, double-slot staggered coupled-cavity TWT. The coordinate system used in the simulation is a rectangular coordinate system (x, y, z). The paper shows a MAGIC3D model of a double-slot staggered CCTWT circuit. Coupling slots are cut into the wall to separating the cavities. There are two slots rotated 180 degrees about the beam axis in the same wall. The slot location is staggered by 90 degrees for successive walls. The CCTWT employed a reentrant double-slot staggered RF cavity structure. The choice of double staggered slots was made because of the wide frequency bandwidth and the moderate interaction impedance.

This paper shows that the magnetrons are widely used microwave sources due to advantages of low cost and high efficiency. Two- and three-dimensional simulation studies have been performed on the A6 relativistic magnetron developed at the Massachusetts Institute of Technology (MIT). Experimental and simulation reports of magnetic priming effects for microwave oven magnetron and relativistic magnetrons have been published. It investigated the frequency tunable A6 relativistic magnetron with metal tuner. Inductive tuning is accomplished by inserting conducting rods axially into the resonators in regions where the RF magnetic field is high. In this paper, we discuss the operating characteristics of a frequency tunable relativistic magnetron by the use of a three dimensional PIC code and MAGIC3D.

This paper describes fabrication and experiment of 1.5 kW pulsed solid-state power amplifier (SSPA) with automatic gain equalization circuit for radar application. The 1.5 kW pulsed SSPA consists of two RF power amplifier module (PAM). Each RF power amplifier module has a series 8-cascaded power amplifier. Final RF output power is combined by hybrid ring combiner. Overall dimension of Pulsed SSPA is 39times29times15.6 cm3. Experimental results show peak output power of 1.53 kW, corresponding to PAE of 29% over a frequency range of 2.7 -3.1 GHz with a pulse width 100 musec and a PRF of 1 kHz.

This paper describes fabrication and experiment of a 1.5 kW solid-state pulsed power amplifier with automatic gain equalization circuit for radar application. The solid-state pulsed power amplifier consists of parallel RF power modules to obtain a high RF power of more than 1.5 kW. Each power module has a series 8-cascaded power amplifier. Overall dimension of the amplifier is 39x29x15.6cm3 . Experimental results show peak output power of 1.8 kW, corresponding to PAE of 25% over a frequency range of 2.7 - 3.1 GHz with a pulse width of 100 musec and a PRF of 1 kHz.

This paper presents the beam emission test of a triode-type Pierce gun pasted with a carbon nanotube (CNT). A DC emission current from the gridded-CNT cathode was measured to be 4.2 mA where the applied cathode voltage is -0.86 kV, grid and anode are ground, and cathode-to-grid distance is 200 μm. We also examined the triode field emission characteristics with two accelerating stages. The pulsed current emission of 2.8 mA was measured where a cathode voltage is -4 kV, cathode-grid potential difference is 1.38 kV, and pulse width is 100 μs.

This paper describes the design and performance of a 1.5 kW solid-state pulsed power amplifier, operating over 2.7-2.9 GHz at a duty of 10 percent and with a pulse width of 100 us for radar application. The solid-state pulsed power amplifier configures a series of 8-stage cascaded power amplifiers with different RF output power levels. Low loss Wilkinson combiners are used to combine output powers of six 300 W high power solid state modules. Tests show peak output power of 1.61 kW, corresponding to PAE of 26.2 % over 2.7-2.9 GHz with a pulse width of 100 us and a PRF of 1 kHz.

A KOMAC (Korea Multipurpose Accelerator Complex) klystron tube operating with a maximum output power of 1 MW at 700 MHz is analyzed by the use of 2-D particle-in-cell code, MAGIC in order to validate the design parameters.

Significant reduction of noise figure can be realized by partitioning the high TWT gain about equally between the SSA (solid state amplifier) and the TWT. We report the design study and experimental results of an X-band power amplifier module, consisting of a low-noise SSA and a low-gain helix-TWT. The module consists of the low noise SSA and a low gain TWT. The SSA is a two-stage amplifier where the second stage is configured as a balanced amplifier. The balanced amplifier is designed for achieving a low VSWR and doubling the amplifier power. The active devices of first and second stage amplifiers are a NEC low noise hetero-junction FET and two Mitsubishi power GaAs FETs. The TWT produces a maximum amplified power of 14 W, corresponding to saturated gain of 25.4 dB and efficiency of 21.6 % with a single stage depressed collector.

An X-band helix traveling wave tube (TWT) amplifier is designed, fabricated and tested. X-band helix circuit is designed by the use of the Sheath helix theory and HFSS code. A cold-test helix circuit is fabricated and tested to examine TWT dispersion characteristics and beam wave interaction impedance.

In this paper, design and experimental study on X-band power amplifier module, consisting of a low-noise solid state amplifier and a low-gain helix-TWT were presented. The overall module gain is designed to be 45 db for SSA and 27 db for TWT, respectively.

A high power rising-sun magnetron oscillator is designed to operate at 9.5 GHz. A time evolved electron flow exhibits nine space charge spokes in the MAGIC3D PIC simulations, which confirms the /spl pi/-mode oscillation in the eighteen vanes rising-sun magnetron. We investigated five operating points for /spl pi/-mode by the use of the PIC code. Simulations show that the highest efficiency is 74% at 36 W, 6.5 kG corresponding to a magnetron power of 530 kW where the oscillation frequency and anode current are 9.502 GHz and 20 A, respectively. Comparison of MAGIC3D simulation results and experiments is presented.

Summary form only given. Design of a Q-band travelling-wave tube amplifier is presented in this paper. Two types of slow wave circuit with folded-waveguide type and helix type are examined in the traveling-wave-tube amplifier. A 3D particle-in-cell code (MAGIC3D), a 3D electromagnetic code (HFSS) and Pierce theory are used in the amplifier design. A highly reproducible, low cost folded-waveguide traveling-wave-tube amplifier is designed to operate at 40-48 GHz with a peak output radiation power of 200 W. Initial circuit parameters are obtained from the Pierce theory and circuit dispersion relations. A non-linear, large-signal performance of the amplifier is predicted from the 3D particle-in-cell simulation. A simulation model of the two stage serpentine circuit is shown. The non-linear numerical simulations predict an electronic efficiency of 5.6%, corresponding to a saturated radiation power 200 W at 44 GHz where the beam voltage is 21 W and the beam current is 0.17 A. The saturated 3-dB bandwidth is found to be 16% (40.5-47.5 GHz). A design of a Q-band helix traveling-wave-tube amplifier is underway.

Experiments on a 28 GHz, five cavity gyroklystron amplifier are underway. Initial hot tests show that the stable amplified radiation produces a peak power of 50 kW at 27.85 GHz. A strong oscillation in the output cavity with power exceeding 200 kW is measured near the amplifier operating point. A careful magnetic field tuning near 10 kG is currently underway to optimize the amplifier performance. Experimental results and comparison with numerical simulation results are presented.

A high power five-cavity gyroklystron amplifier operating at 28GHz is under development at KBSI. The amplifier consists of a high power magnetron-injection-gun (MIG), a hybrid coaxial input coupler, three idler cavities, an output cavity, and a beam collector. Numerical codes used in the amplifier design include large-signal non-linear codes for amplifier gain and efficiency calculations, a 3-D electromagnetic simulator (HFSS), a thermal analysis code (ANSYS), and an electron trajectory code (EGUN).

An X-band microwave amplifier module consisting of a low-noise solid-state amplifier and a low-gain helix traveling-wave-tube (TWT) is designed and fabricated. Measured microwave characteristics are found to be significantly improved compared with conventional helix-TWTs.