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In this paper, we present a detailed analysis of the iterative phase retrieval approach (IPRA) for determining the phase profile of the output microwave beam of a gyrotron from known intensity patterns emphasizing the field propagation techniques which are used to propagate the RF field of the microwave beam between known intensity planes. The propagation method, based on first Rayleigh--Sommerfeld diffraction integral (RSDI), is solved using fast Fourier transform (FFT) technique and zero padding. It is observed that the use of FFT and, therefore, the discretization of the RSDI propagation kernel introduce aberrations in the propagated field due to the superposition of the original field with its replicated versions. This problem is solved by approximations leading to the Huygens--Fresnel propagation method which further imposes the restrictions on the distances of propagation depending on the size of the transverse plane used to discretize the intensity pattern. This constraint of the distance of propagation causes problem in the iterative phase retrieval approach (IPRA) when more than two intensity planes are used. A method based on interpolation is proposed to overcome this restriction. IPRA is then further discussed to optimize several parameters, such as plane separation, plane dimension, mesh size, and measurement accuracies, which become more of an issue during the measurements of infrared intensity thermograms of the output microwave beam. Index Terms--Fourier transform, gyrotron, infrared intensity thermogram, millimeter wave, phase retrieval, zero padding.

The experiment on a Ku-band gyrotron backwardwave oscillator (gyro-BWO) with a single depressed collector and linear polarization mode output has been performed successfully. Stable magnetic tuning bandwidth of 5% and maximum power of 48 kW under a 40-kV 11.5-A electron beam were achieved. The overall efficiency of the gyro-BWO with a single stage depressed collector has been enhanced from 10.5% to 21%. The measured performance has demonstrated a strong potential of the gyro-BWO for new application requiring high-power tunable wave source. Index Terms--Broadband tunability, depressed collector, gyrotron backward-wave oscillator (gyro-BWO), high-power millimeter wave.

We measure and characterize the 55-65 GHz wireless channel for a typical desktop environment. The Saleh-Valenzuela (S-V) model is used to describe the desktop environment. Key S-V model parameters such as cluster decay factor, ray decay factor, cluster arrival rate, and ray arrival rate are extracted from measured data. Index Terms--Millimeter wave propagation, multiple-path channel, radio propagation.

The modeling and design aspects of Josephson junction arrays involving millimeter wave power generation is discussed.

The micro-mechanical and electrical characterization of a surface mounted niobium (Nb) MEMS technology that could be integrated with a wide range of cryogenic semiconductor and superconducting circuits is presented.

A novel folded waveguide that characteristics thick iron pole pieces with hollow centers is built as part of a periodic-permanent-magnet-focused W-band single-stage test-vehicle traveling-wave tube (TWT).

The accuracy of a phase-retrieval procedure for microwave beams was analyzed and verified using an 84-GHz quasi-optical beam transmitted by a corrugated waveguide. The output intensity and phase profiles of the beam were directly measured with a microwave receiver. The beam intensity was also measured at several planes and the data were used with a phase-retrieval algorithm to yield an independent estimate of the phase. Moment and matching coefficient methods were used to analyze the retrieved profiles. In the higher order moment analysis, the intensity profiles, which were calculated from the retrieved phase profiles, coincided well with the measured profiles in terms of the beam size, asymmetric property (skewness), and flatness/peakedness (kurtosis) over the entire profile. Analysis indicated that the mode content of the beam obtained by phase retrieval matched that of the direct measurement with a matching coefficient of 0.97 using both the intensity and phase profiles. Index Terms--Electron cyclotron heating (ECH), Gaussian beam, gyrotron, phase measurement, phase retrieval, quasioptical mirror.

The Naval Research Laboratory W-band Advanced Radar for Low Observable Control (WARLOC) is a high-power 94-GHz radar, with 3-10-kW average and 80-kW peak power, now set up on the western shore of the Chesapeake Bay. It has three orders of magnitude more power and sensitivity than other W-band radar systems. This enables cloud reflectivity to be measured with high signal-to-noise ratios and a resolution of about 15 m over a two (or three)-dimensional region, which can be as large as tens of kilometers on a side. This allows imaging of the internal structure of clouds over great distances in very great detail. At the shortest scale lengths, the structure has a speckle pattern indicating that it is governed at least in part by stochastic processes. The WARLOC data allow the reflectivity correlation function and its Fourier transform, which is the power spectrum, to be computed for scale lengths ranging from 30 m to 10 km. For measurements taken of cirrus clouds on several occasions as well as one case of a precipitating cloud, it was found that for small correlation distance r, the correlation function usually decreases as [r.sup.2/3], or, equivalently, the wavenumber spectrum scales as [k.sup.-5/3], where k is the wavenumber. This suggests that fluid turbulence in the inertial range is playing a role; however, unlike classical fluid turbulence, the results suggest that the turbulence here is generally quite anisotropic. Furthermore, for longer scale lengths (the outer range according to the Kolmogorov theory), the reflectivity fluctuations usually show a wavelike behavior in the vertical direction but only occasionally in the horizontal direction. Index Terms--Clouds, gyrotrons, millimeter-wave radar.

This brief presents a design method of a millimeter-wave CMOS radiation oscillator for broadband short-range communication. An above-chip patch antenna is proposed for the radiation oscillator. The proposed antenna has a balanced port, which makes it suitable for the direct connection of CMOS cross-coupling transistors. The properties of the antenna are analyzed by an electromagnetic field solver, and, in particular, the input resistance is discussed in detail, so that the condition of millimeter-wave oscillation is satisfied even by CMOS FETs having gains lower than GaAs FETs. Furthermore, on/off-keying modulation can be carried out using switch transistors, and two switching techniques are used to realize a large data rate. A performance of 500 Mb/s and a total efficiency of 0.12, which includes both the antenna and the circuit efficiencies, are confirmed by circuit simulation. Index Terms--Balanced structure, broadband communication, CMOS integrated circuit, microstrip patch antenna, millimeter-wave, radiation oscillator, short-range communication.

70-GHz-band orthogonal frequency-division multiplexing (OFDM) transceivers were developed by combining self-heterodyne transmission with two-element diversity reception. The transceivers were used to study and demonstrate a millimeter-wave wireless personal network that enables cost-effective broadband data transmissions in a multipath channel environment. A 100-MHz sampling OFDM modulator/demodulator was developed for the baseband part. It has a payload data rate of 100 Mb/s using quadrature phase-shift keying (QPSK) modulation and a coding rate of 3/4 (many other modulations and coding rate are available). The bit error rate was experimentally evaluated when a pair of devices was placed on a wooden table under line-of-sight path conditions. The results showed that the combined use of the self-heterodyne technique and two-element diversity receiver successfully avoids serious signal fading at unpredictable transmission distances. The transceiver with QPSK modulation and coding rate of 1/2 for forward error correction achieves error-free data transmission over a distance of up to 3.4 m. In addition, a successful transmission in 64 quadrature amplitude modulation mode was demonstrated, although the communication range was quite short. Index Terms--Combining diversity, millimeter wave, orthogonal frequency-division multiplexing (OFDM), self-heterodyne, wireless personal area network (WPAN).

A heterostructure barrier varactor subharmonic upconverter is investigated for the first time. Odd sidebands are suppressed due to the symmetric capacitance--voltage (C-V) characteristic of the varactor and high output power is possible through epitaxial stacking of barriers. The upconverter is pumped using a millimeter-wave local oscillator, and can be used as a transmission-type double-sideband suppressed carrier modulator. The initial measured conversion loss is 8-16 dB at 100 and 200 GHz. The results are significantly improved by using external impedance tuners, which is verified through both simulations and measurements. Index Terms--Converters, heterostructure barrier varactor (HBV), millimeter-wave modulation, varactors.

In this paper, we present a cost-effective chip-scale packaging solution for a 60-GHz industrial-scientific-medical band receiver (Rx) and transmitter (Tx) chipset capable of gigabit-per-second wireless communications. Envisioned applications of the packaged chipset include 1-3-Gb/s directional links using amplitude shift-keying or phase shift-keying modulation and 500-Mb/s-1-Gb/s omni-directional links using orthogonal frequency-division multiplexing modulation. This paper demonstrates the first fully package-integrated 60-GHz chipset including receive and transmit antennas in a cost-effective plastic package. A direct-chip-attach (DCA) and surface mountable land-grid-array (LGA) package technology is presented. The size of the DCA package is 7 x 11 [mm.sup.2] and the LGA package size is 6 x 13 [mm.sup.2]. Optionally, the Tx and Rx chip can be packaged together with Tx and Rx antennas in a combined 13 x 13 [mm.sup.2] LGA transceiver package. Index Terms--Chip-scale packaging, low cost, millimeter wave, silicon germanium, wireless communication.

The frequency-tunability for a Smith-Purcell free-electron laser oscillator in the millimeter wave region is enhanced with the aid of a quasi-periodic distributed Bragg reflector (DBR) made of metallic waveguide gratings with rectangular grooves. For a quasi-periodic DBR, the grating parameters are adjusted by means of genetic algorithms to get the desired reflection coefficient, thus compensating for the frequency dependence of the overall output characteristics. For a typical numerical example, flat output characteristics have been obtained over 10% bandwidth around the center frequency 121 GHz. Index Terms--Metallic Bragg reflector, millimeter waves, Smith-Purcell free-electron laser (FEL), tunability.

In this paper, a novel active integrated conical horn array is presented. Specifically, a 95 GHz quasiopticaily fed mixer integrated with an annular slot ring antenna was used as the basic element of the proposed active system. For efficient reception, a low cost micro-machined conical horn array was fabricated and placed on the top of active elements. A modified nonorthogonal finite-difference time-domain (FDTD) approach was applied for analyzing the basic conical horn antenna and a hybrid matrix manipulation technique for efficient antenna array modeling. The proposed active conical horn antenna array was fabricated and measured. Numerical simulations have verified the design at its distributed stages presenting very good agreement with the experimental data. Index Terms--Antennas, array, finite-difference time-domain (FDTD), millimeter wave, submillimeter wave.

This paper presents a novel orthomode-transducer (OMT) architecture, which is particularly suitable for correlation receivers at millimeter waves. By exploiting an on-axis reverse-coupling structure, a compact OMT configuration is obtained, which provides high levels of channel equalization. The Ka-band prototypes exhibit very good electric performances in terms of isolation, cross-polarization, return loss, and channel equalization. Index Terms--Millimeter waves, orthomode transducers (OMTs), radiometers, waveguide components.

This paper presents a 2 x 2 beam steering antenna with circular polarization at 61 GHz for high speed communications. It demonstrates approximately 14 dBi directivity and twenty degree half power beamwidth. The cross polarization is at least 14 dB. Design method, simulation, manufacture and characterization of the antenna are presented. The proposed small-scale array antenna is suitable for various high speed wireless applications. Index Terms--Antenna arrays, beam steering, ceramics, circular polarization, millimeter wave.

Byline: Hiroyuki Tsuji (1), Masayuki Oodo (1), Ryu Miura (1), Mikio Suzuki (1) Keywords: digital beamforming; millimeter-wave; multi-beam-horn antenna; stratospheric-platform Abstract: In this paper, we describe intelligent beamforming antenna systems that can be used in the millimeter-wave band for High-altitude platform systems. We have developed two antenna systems for the millimeter-wave band and have designed experiments to test the efficiency of the developed systems. One is a multi-beam-horn antenna that enables high-speed transmission, and the other is an array antenna that digitally controls antenna beams. These antenna systems are also designed to work in the stratosphere. We also describe our solutions to the problems of low temperature and low pressure and show that the two antenna systems can function well in the stratosphere through tests conducted on the ground. Author Affiliation: (1) National Institute of Information and Communications Technology (NICT), 3-4 Hikari-no-oka, Yokosuka, Kanagawa, 239-0847, Japan Article History: Registration Date: 01/01/2005 Article note: On April 1, 2004, the Communications Research Laboratory (CRL) and the Telecommunications Advancement Organization of Japan (TAO) merged to create NICT. Hiroyuki Tsuji received the B.S., M.S., and Ph.D. degrees from Keio University in 1987, 1989, and 1992, respectively. Since 1992, he has been working in the Communications Research Laboratory, Independent Administrative Institution, Japan. In 1999, he was a visiting researcher at University of Minnesota. He is now a senior researcher of Wireless Innovation Systems Group in the Yokosuka Radio Communications Research Center of NICT (National Institute on Information and Communications Technology, reorganized from CRL in April 2004). His research interests are in array signal processing, particularly as applied to communications. He received the IEICE 1996 Young Engineer Award. He is a member of IEICE and IEEE. Masayuki Oodo was born in Osaka, Japan, on February 1, 1969. He received B.E., M.E. and D.E. degrees in Electrical and Electronic Engineering from Tokyo Institute of Technology, Tokyo, Japan in 1992, 1994 and 1997, respectively. In 1997, he joined the Communications Research Laboratory (CRL, now part of the National Institute of Information and Communications Technology, or NICT), where he has been researching array antennas for wireless communication and frequency-sharing issues between HAPS and other systems. Dr. Oodo received the Paper Presentation Award from IEICE Japan in 1995, the Young Scientist Award from URSI in 1996, the Young Engineer Award from IEICE Japan in 1997, and the Young Engineer Award from IEEE AP-S, Tokyo Chapter in 1998. He is a member of IEEE. Ryu Miura received the B.E., M.E., and PhD degrees in Electrical Engineering from Yokohama National University, Yokohama, Japan, in 1982, 1984, and 2000, respectively. He joined Communications Research Lab (CRL), Ministry of Posts and Telecommunications, Tokyo, Japan in 1984, where he worked for research on mobile satellite communication systems using the Engineering Test Satellite, ETS-V. During 1991--1992, he was a visiting researcher in AUSSAT, Pty. Ltd. (now Optus, Pty. Ltd.), Sydney, Australia. During 1993--1996, he was a senior researcher in ATR Optical and Radio Communications Research Labs, Kyoto, Japan, where he worked for research on digital beamforming antennas for mobile communications. He is now a group leader of Wireless Innovation Systems Group in the Yokosuka Radio Communications Research Center of NICT (National Institute on Information and Communications Technology, reorganized from CRL in April 2004), where he works for R&amp D on wireless communication systems using stratospheric platforms. Dr. Miura is a member of IEEE and IEICE. Mikio Suzuki received a B.S. degree in electronic engineering from Keio University in 1970. He joined Mitsubishi Electric Corporation in 1970, where he researched and developed microwave integrated circuits and waveguide array antennas for defense radars and missiles. He is now at the NICT Yokosuka Stratospheric Platform Research Center, and his current research interests lie in the system design of applications for wireless communication systems using a stratospheric platform and the development of related communication equipment. He is a member of the IEICE of Japan.

We synthesize amplitude- and phase-type computer-generated holograms (diffractive gratings) for shaping millimeter-wave fields. We design holograms using quasi-optical back-propagation and rigorous optimization methods adopted from diffractive optics. We present experimental results from a plane-wave-generating hologram and a custom-designed field shaper at 310 GHz. Holograms can be applied, e.g., in a compact antenna test range and we propose their use for alignment purposes. Index Terms--Beam steering, diffraction, holographic gratings, millimeter-wave technology, propagation, submillimeter-wave technology.

This paper presents a theoretical and experimental study of the nonlinear effects generated RF-microelectromechanical system (MEMS) varactors and capacitive switches. The theoretical part includes an analytic derivation, as well as an electromechanical model suitable for computer-aided design (CAD) simulation. The simulations agree very well with measurements performed on a 24-GHz three-pole MEMS tunable filter. It is shown that MEMS capacitive components with a spring constant k > 10 N/m generate very low intermodulation, as compared to semiconductor devices, and lead to a two-tone third-order intermodulation intercept point (IIP3) greater than +40 dBm for [DELTA] 3-5 [f.sub.o], where [f.sub.o] is the mechanical resonant frequency. In fact, the IIP3 increases to +80 dBm for a difference signal ([DELTA] f) of 5 MHz. The CAD model also allows the evaluation of the power-handling capabilities of the tunable filter and, it is seen that, for the case presented here, distortions become significant for an input power greater than +20 dBm. Noise generation due to thermal effects on a movable membrane (Brownian noise) is also modeled and it is shown that the tunable filter results in a very low phase-noise level close to the carrier. Index Terms--Filters, intermodulation (IM), microelectromechanical system (MEMS), microwave, millimeter wave, phase noise, power handling, switches, varactors.

Low-loss high dielectric-constant materials are analyzed in the terahertz frequency range using time-domain spectroscopy. The dielectric constant and loss tangent for steatite, alumina, titania loaded polystyrene, and zirconium--tin--titanate are presented and compared to measurements on high-resistivity silicon. For these materials, the real part of the dielectric constant ranges from 6 to 90. All of the samples were found to have reasonable low-loss tangents. Applications as photonic crystal substrates for terahertz frequency antenna are envisaged. Index Terms--Antennas, dielectric materials, measurements, submillimeter waves.

This paper concerns an optical millimeter-wave signal generator for fiber-based millimeter-wave systems. The millimeter-wave signal generator is based on two-mode injection locking of a Fabry-Perot (F-P) laser. The millimeter-wave signal can be induced by self-heterodyne detection of the locked two modes in a high-speed photodetector (PD). The locking characteristics of the F-P slave laser and the tunability for the millimeter-wave carrier frequency are demonstrated. When the F-P laser is directly modulated by data signals, the locked two modes are modulated simultaneously. The data signals can then be up-converted to the millimeter-wave band at the PD output. By this direct modulation method, the effect of fiber chromatic dispersion on the millimeter-wave signal components at the PD output can be moderate according to mixing of amplitude and phase modulation on the locked two modes. In virtue of the wide response of the F-P laser, relatively high-speed data (2.5 Gbit/s nonreturn to zero (NRZ)-ASK or 622 Mbit/s NRZ-BPSK) on the millimeter-wave band (52 or 60 GHz) can be transmitted on a 32-km single-mode fiber without bit error. A wide tunable range (56-63 GHz) for the central frequency of the millimeter-wave signals and a wide optical bandwidth (1530-60 nm) of the F-P slave laser are also confirmed by the bit-error measurements of the transmitted data signals. Index Terms--Fabry-Perot (F-P) lasers, fiber-radio systems, millimeter-wave links, optical generation of millimeter-wave signals.

This paper introduces new techniques and architectures for the implementation of linear slot arrays on electrically thick dielectric substrates at millimeter-wave frequencies. The slot arrays are fed by a coplanar waveguide series line and lead to high gain by utilizing the phase cancellation technique to reduce coupling to the dominant surface-wave mode. Unlike traditional designs, no meander lines are used in the proposed structures, easing their fabrication by eliminating the need for air bridges and leading to patterns with low cross-polarization and high gain. In addition, the option of including a backing ground reflector to render the patterns unidirectional is explored and implemented. In this latter case, it is shown that simultaneous reduction of the dominant surface-wave and TEM modes through phase cancellation can be achieved. The design of the proposed arrays is based on an intuitive transmission-line model, which enables the implementation of arrays with a gradual current taper and, thus, maximum gain. This study is verified experimentally around a nominal frequency of 27.8 GHz. Index Terms-Integrated-circuit antennas, meander lines, millimeter waves, series feeding, slot arrays, surface waves, wireless links.

The authors examine possible solutions to the problem of electron-wave interaction. Topics include millimeter wave research, temperature regimes, and efficiency .

In this paper we present a three-cavity design of a gyroklystron amplifier at 95 GHz. We present the design of the magnetron injection gun (MIG), the magnetic field coils, and the three-cavity microwave circuit. The MIG produces a 500 kV, 45 A small-orbit annular beam with an average perpendicular-to-parallel velocity ratio of 1.5 and a parallel velocity spread below 5% (RMS). The MIG requires a control anode with a voltage of about 65 kV, a magnetic compression of about 30, and a cathode loading near 10 A/[cm.sup.2]. The circuit magnetic field is about 28.7 kG. The microwave circuit has a first-harmonic [TE.sub.011] input cavity which is driven at 47.5 GHz, and second-harmonic [TE.sub.021] buncher and output cavities which are resonant at 95 GHz. A peak power of 7.56 MW is obtained with 51.6 dB gain and 33.6% efficiency. A complete description of the system is presented along with a systematic study of the sensitivity of the device to parametric variations. Index Terms - Amplifiers, gyrotrons, HPM, microwave sources, millimeter waves.

A large orbit gyrotron with a 300 keV, 30 A, 20 ns electron beam has provided selective generation with radiation power from 1.5 MW at fundamental (wavelength of 14 mm) to 100 kW at the fifth cyclotron harmonic (wavelength of 4 mm). The next experiment with unique electron beam (250 keV, 18 A, 10 [[micro]seconds], 0.6 mm in diameter) is in progress. Index Terms - Axis-encircling electron beam, cyclotron resonance maser, high-harmonic gyrotron, kicker, large-orbit gyrotron (LOG), mode interaction, relativistic gyrotron.

The scaling of operating parameters and the tendencies in the efficiency of the step-tunable gyrotron operating in a set of modes in a cavity of a given length are considered. Results of calculations are reported for design of a [similar to]1-kW, step-tunable gyrotron oscillator operating from 150 to 600 GHz in steps of about 15 GHz. Detailed results are presented for the efficiency, power losses in the cavity, and the starting conditions. Designs of the electron gun electrodes and of an output mode transducer are also presented. Full modulation of the radiation via the modulating anode of a magnetron injection gun is considered. The gyrotron would be of use for plasma diagnostics and spectroscopy, including electron paramagnetic resonance spectroscopy (EPR). Index Terms - Cyclotron, gyrotron, millimeter waves, radiation.

A novel waveguide-to-microstrip transition is developed using a new design methodology based on iris coupling. Key features of the design are a single-layer substrate, new matching topology, and new cavity enclosure. The transition lends itself to a low-cost implementation, while maintaining the enclosure's hermetic integrity. An extensive tolerance study shows that the present design is robust and very stable with respect to manufacturing and assembly variations. Careful consideration has been given to the mechanical aspects of the transition's implementation in order to achieve seamless integration into the overall package manufacturing and assembly process without sacrificing electrical performance. Proof of concept was achieved by implementing a Q-band ([f.sub.0] = 44.5 GHz) design on alumina, a IV-band ([f.sub.0] = 94 GHz) design on z-cut quartz, and a W-band design on fused silica. All exhibited better than 22-dB return loss at their center frequencies with less than 0.3-dB insertion loss, and at minimum a 10% 15-dB return-loss bandwidth. Index Terms - Microwave integrated circuits, MMIC's, waveguide discontinuities, waveguide transitions.

This paper demonstrates a deembedding technique and a direct on-substrate measurement technique for fast and inexpensive characterization of miniature antennas for wireless applications at millimeterwave frequencies. The technique is demonstrated by measurements on a tapered slot antenna (TSA). The measured results at Ka-band frequencies include input impedance, mutual coupling between two TSA's, and absolute gain of TSA. Index Terms - Gain, input impedance of antenna, linearly tapered slot antenna, mutual coupling, on-wafer characterization, TRL calibration standards.

A new form of a measurement setup for shielding gaskets at microwave and millimeter-waves is proposed. Parallel metal plates separated by a center dielectric rod is used as a transmission line in which the gasket sample is placed to block wave propagation. The shielding effectiveness is determined by the transmitting power through the sample. By this setup, the shielding evaluation can be made over the frequency range from 13 to 110 GHz. The field distributions along the sample calculated based on a dielectric antenna theory and the measurements results for some gasket samples are described. Index Terms - Electromagnetic shielding, millimeter-waves, shielding gasket.

A method for calculating antenna-reflector combination gain for rectangular reflectors operating in the Fresnel region is derived instead of an approximate method based on an equi-area circular reflector. The scope of microwave application of the method is discussed, and reflector-equipped microwave links in operation are examined using the new method. A field test result using 50-GHz radio equipment with four types of reflectors shows good agreements with the theoretical calculations.

The first coherent measurement of submillimeter-wave sideband generator (SBG) output power is reported here. This SBG utilizes a submillimeter laser, microwave synthesizer, and high frequency Schottky diode to produce tunable radiation. Record efficiency and output power (10.5 [micro]W) at a drive frequency of 1.6 THz has been obtained, and SBG radiation was efficiently separated from the laser driver with Si etalons. The power measurements were made using a dual C[O.sub.2]-Submillimeter laser system and two Schottky diodes, one as the sideband generator and one as the receiver. The SBG efficiency of four different models of University of Virginia (UVa) diodes were studied and the first measurement of the output mode of the sideband (without the unshifted laser present) was also performed. Finally, confirmation of the optimal parameters for coupling a Gaussian beam into a corner-reflector mounted Schottky diode is presented.

We discuss critical aspects of imaging system design and describe several different imaging systems employing focal plane array receivers operating in the 3mm-2mm wavelength range. Recent progress in millimeter-wavelength optics, antennas, receivers and other components permits greatly enhanced system performance in a wide range of applications. We discuss a radiometric camera for all-weather autonomous aircraft landing capability and a high sensitivity cryogenically cooled array for use in radio astronomical spectroscopy. A near-focus system for identification of plastic materials concealed underneath clothing employs a two element lens, and has been demonstrated in active (transmitting) and passive (radiometric) modes. A dual mode imaging system for plasma diagnostics utilizes both active and passive modes at its approximately or equal to 140 GHz operating frequency to study small-scale structure. The radiometric imaging systems employ between 15 and 256 Schottky barrier diode mixers while the imaging receivers for the active systems include 64 element video detector arrays.

The characteristics of a dielectric probe for scanning near-field millimeter wave microscopy are presented. The dielectric probe is fabricated from Teflon and shaped like a cone and the beam profile of the millimeter-wave radiated from the tip of the Teflon probe is measured by three-dimensional scanning using a different Teflon probe.

The development of antenna-coupled bolometers using Transition-Edge Sensors (TES) for millimeter waves is reported. The results of the electrical and optical characterization of single bolometers pixels are presented.

Diffraction effects, which occur when the fields in a beam waveguide are truncated at absorbing stops, can be conveniently analyzed using scattering-matrix theory applied to Gaussian-beam modes. We present recursion relationships for the elements of the scattering matrix when a nonaxially-symmetric beam illuminates an axially symmetric stop. We demonstrate the technique by calculating the total loss and beam profiles in a system comprising a diagonal horn, a lens, a window, and two off-axis mirrors. The finite size of each component is taken into account.

A high-sensitivity technique is used for time-resolved imaging of millimeter waves (MMWs) by using the visible continuum (VC) from the positive column (PC) of a medium-pressure Cs-Xe dc discharge. The modeling of the transient behavior of the electron temperature in the PC has shown that the time history of the electron temperature variation has coincided well with the measured time history of the VC intensity variation.

The changes in the transmission modulus and phase of the propagating microwave signals in a micromachined coplanar waveguide supported on a dielectric membrane filled with a mixture of carbon nanotubes when exposed to nitrogen gas are examined. The large shifts of amplitude and phase of microwave signals due to gas absorption have represented a basis on which a miniature wireless gas sensor is implemented.

Ex situ spectroscopic ellipsometry (SE) method is used for investigating the structure of metal-free carbon nanotube (CNT) films grown on carbon-face 4H-SiC by thermal decomposition. The growth rate of the CNT is shown to be function of growth pressure, which is related to the residual oxygen in the chamber.

The atmospheric discharge from a 170 GHz millimeter-wave beam using a high-speed framing camera and the relationship between the thrust performance ionization front propagation are investigated. The momentum coupling coefficient [C.sub.m] value is found to be greater than 350 N M[W.sup.-1] when the ionization fAont propagated with supersonic velocity.

A study was conducted to examine the response of a Yba(sub 2)Cu(sub 3)O(sub 7-x) (YBCO) thin film microbridge to millimeter wave radiation. The YBCO high resistivity samples with low viscous drag coefficient have a -3 dB roll-off frequency value of about several gigahertzes.