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A satellite microwave emission brightness temperature histograms (METH) technique has been applied to Special Sensor Microwave Imager (SSM/I) data taken on board the Defense Meteorological Satellite Program (DMSP) satellites and preprocessed by Remote Sensing Systems (RSS) Co. to produce 21 yr (July 1987-present) of oceanic rainfall products. These rain products are used as input to the Global Precipitation Climatology Project (GPCP) rain maps. Analysis of the METH product using SSM/I version-4 (V4) data shows jumps in vertically polarized 19-GHz brightness temperatures that are attributed to changes in DMSP satellites. A version-6 (V6) SSM/I that corrects for intersatellite differences was released by RSS in 2006. The jumps in the time series are reduced, with most of the changes occurring in the early part of the DMSP F13 data. The bias between RSS V6 and V4 of brightness temperature at 19 and 22 GHz is less than 0.5 K. METH rain rates were reprocessed using V6 data and were analyzed. The 20-yr global mean difference between the METH V4 and V6 is less than 0.3%, with differences as large as 3% in individual years. Trend analyses show increases in the oceanic rain belts, such as the intertropical convergence zone and the South Pacific convergence zone, and in the Bay of Bengal. These rain-rate trends, from both linear trend analysis and empirical mode decomposition analysis, are comparable to the version-2 GPCP analyses but are smaller than those found in the unified microwave ocean retrieval algorithm. DOI: 10.1175/2009JAMC2204.1

This paper presents two tools for feedforward correction in transmitter chains in software-defined radio. The methods presume that the radio configuration already has a gate array and a mixer juxtaposed with one another. Programming is added in the gate array to affect preconditioning of the signals presented to in-phase and quadrature channels of a hybrid mixer so as to correct and enhance the analog RF performance of the mixer. The first of the methods comprises a realization with off-the-shelf components of feedback of the RF output of the mixer. Spectrum analysis in the gate array allows separation and cancellation of the unwanted difference-frequency sideband in the mixer's output. The second tool is a feedforward correction of imperfect performance of a hybrid mixer. The correction parameters are determined through sideband reduction via the feedback scheme in the first method. It is shown that the correction scheme performs well even for very large deviations from the ideal in the mixer parameters. As a consequence, the scheme may be used to extend the operating band of the gate-array/mixer combination to extreme bandwidths--approaching 200%. Index Terms--Gate array, hybrid junctions, microwave mixers.

Simulated sea ice was grown in an outdoor tank during the early winter seasons of 2001/2002 and 2005/2006. Microwave radiation was sampled every 5 min from the following three channels: 19, 37, and 85 GHz. Surface physical conditions were measured or observed to help in the interpretation of the radiometric behavior. This paper reports on results related to the following objectives: 1) linking the observed radiation to surface properties and processes; 2) classifying thin ice into emissivity-based surface types, and 3) assessing thin-ice parameter retrieval algorithms. This paper shows that ice of less than 4-cm thickness exhibits cycles of a sharp decrease of microwave emission caused by surface wetness followed by a gradual increase as the surface refreezes. This ice is particularly linked to meteorological conditions. Snow accumulation on relatively thick ice (> 20 cm) affects only the radiation from the 85-GHz channel. Thin-ice surfaces can be grouped into two radiometrically distinguished categories--the first includes slushy and wet surfaces and the second includes wet snow, dry snow, and dry bare-ice surfaces. Radiation from the second category is higher. The radiation from a refrozen slush surface appears to fall between these two categories. The variability of emissivity increases as the radiation frequency increases, particularly for the horizontal polarization channels. Existing algorithms of ice thickness, snow depth, and ice concentration were examined against the current data to study their sensitivity to variations of surface conditions. Limitations on their applications have been established. Index Terms--Ice parameter retrieval, microwave emission from ice and snow, passive microwave, sea ice, thin ice.

A new transmission-line method has been developed which is used to determine the propagation constant of a novel microwave material. Rather than requiring two or more transmission-line lengths to determine the propagation constant of a material, our method relies on a single fixture of known length and the use of a dielectric material of known properties to set a baseline measurement. By using a single fixture to make the measurements, we avoid introducing additional parasitic elements that would produce errors. We applied this approach to find the dielectric constant of the polymer Polydimethylsiloxane over a frequency range of 0.1-40.0 GHz. Index Terms--Broadband de-embedding, complex permittivity, dielectric constant, polydimethylsiloxane (PDMS), propagation constant, single-length method, Sylgard 182.

An analytic formulation of dynamic electro-thermally induced nonlinearity is developed for a general resistive element, yielding a self-heating circuit model based on a fractional derivative. The model explains the 10 dB/decade slope of the intermodulation products observed in two-tone testing. Two-tone testing at 400 MHz of attenuators, microwave chip terminations, and coaxial terminations is reported with tone spacing ranging from 1 to 100 Hz. Index Terms--Compact modeling, electrothermal, fractional calculus, fractional derivative, heat transfer, intermodulation distortion, multiphysics modeling, nonlinear computer-aided design (CAD), passive intermodulation distortion (PIM), thermal model, transient.

Seto et al. developed rain/no-rain classification (RNC) methods over land for the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). In this study, the methods are modified for application to other microwave radiometers. The previous methods match TMI observations with TRMM precipitation radar (PR) observations, classify the TMI pixels into rain pixels and no-rain pixels, and thenstatistically summarize the observed brightness temperature at the no-rain pixels into a land surface brightness temperature database. In the modified methods, the probability distribution of brightness temperature under no-rain conditions is derived from unclassified TMI pixels without the use of PR. A test with the TMI shows that the modified (PR independent) methods are better than the RNC method developed for the Goddard profiling algorithm (GPROF; the standard algorithm for the TMI) while they are slightly poorer than corresponding previous (PR dependent) methods. M2d, one of the PR-independent methods, is applied to observations from the Advanced Microwave Scanning Radiometer for Earth Observing Satellite (AMSR-E), is evaluated for a matchup case with PR, and is evaluated for 1 yr with a rain gauge dataset in Japan. M2d is incorporated into a retrieval algorithm developed by the Global Satellite Mapping of Precipitation project to be applied for the AMSR-E. In latitudes above 30[degrees]N, the rain-rate retrieval is compared with a rain gauge dataset by the Global Precipitation Climatology Center. Without a snow mask, a large amount of false rainfall due to snow contamination occurs. Therefore, a simple snow mask using the 23.8-GHz channel is applied and the threshold of the mask is optimized. Between 30[degrees] and 60[degrees]N, the optimized snow mask forces the miss of an estimated 10% of the total rainfall.

The European Space Agency's Soil Moisture and Ocean Salinity satellite comprises a single payload instrument known as the Microwave Interferometric Radiometer with Aperture Synthesis (MIRAS) coupled to a PROTEUS platform. MIRAS synthesizes a large aperture from a reasonably sized 2-D array of passive microwave radiometers. By using interferometric techniques, the required coverage and spatial resolution can be achieved without the need for a large antenna. This paper describes the MIRAS instrument, its observation modes, the imaging geometry, and data products. Index Terms--Microwave radiometry.

We propose a new method to study high temperature tissue ablation using an expanded bioheat diffusion equation. An extra term added to the bioheat equation is combined with the specific heat into an effective (temperature dependent) specific heat. It replaces the normal specific heat term in the modified bioheat equation, which can then be used at temperatures where water evaporation is expected to occur. This new equation is used to numerically simulate the microwave ablation of bovine liver and is compared to experimental ex vivo results. Index Terms--Ablation, bioheat equation, liver, microwave, specific heat.

This paper presents an analytical, numerical, and experimental analysis of the breakdown strength of microwave gas-filled RF devices containing sharp corners and wedges. For the idealized case of a wedge-shaped geometry, it is shown that only under certain physical circumstances does the singularity and the concomitant strongly enhanced microwave field determine the breakdown strength. In particular, when diffusion is the dominating loss mechanism for the electron density, breakdown is a volumetric process, and the field singularity does not determine the breakdown threshold. In such situations, excessive accuracy in numerical calculations is not required. Conditions for volumetric and localized breakdown, respectively, are established analytically, and the validity is demonstrated by numerical simulations. Finally, the analysis is extrapolated and compared with experimentally observed breakdown thresholds in commercially available resonators of nonidealized geometry. Good agreement between theoretical predictions and experimental results is demonstrated. Index Terms--Corners, corona, electric field singularities, microwave breakdown.

Complex microwave devices (CMD) are compact integrated multifunctional devices, which are capable of providing generation, processing, and amplification of complex multifrequency microwave signals. Design parameters and performance capability for several onboard CMDs are mentioned.

We have determined the nonuniform distribution of the shape-induced magnetic anisotropy field for patterned thin films of Ni-Fe. To do this, we used integrated microstrip structures with different widths on identically patterned Ni-Fe cores to act as probes of the internal magnetic field. We verified the accuracy of the field profiles by comparing them with M-H loop measurements of the magnetic films. Index Terms--Demagnetizing field, magnetic microwave devices, Ni-Fe, shape anisotropy.

To investigate the potential of passive microwave techniques for observing the atmosphere over land, it is important to understand the nature of emissions from the land surface. The heterogeneity of large-scale land surface emissions has been cited as a major impediment in conducting observations of the atmosphere over land. Many models, both theoretical and empirical, have been developed to explain the surface emission with varying degrees of success. In the past, most field-supported research in soil observations using microwave techniques has concentrated on lower frequencies (L-band). This paper reports on a study, supported by field data, that seeks to improve our understanding of surface emission at various frequencies using passive microwave radiometers. This provides a crucial link between remote sensing of the land surface and the atmosphere. We show that it is important to consider shadowing associated with rough wet surfaces. By incorporating shadowing effects, the advanced integral equation model (AIEM) shows remarkable agreement with observations at all frequencies and polarizations. Although the roughness parameters obtained during our experiment correspond to very rough conditions, by including shadowing effects the AIEM model is able to transition from the not so rough natural condition as observed from space to the very rough as obtained during field experiments. Index Terms--Microwave, periodic roughness, shadowing, surface emission modeling.

Brightness temperatures over the Amazon rainforest are obtained from the Advanced Microwave Sounding Units (AMSU-A and AMSU-B) instruments onboard three NOAA satellites (NOAA-15, -16, and -17, respectively) for the months of July, August, and October, 2002. The three AMSU-A instruments provided six daily measurements, separated by 2.5-5.5 h of the diurnal time intervals, over the Amazon rainforest region, and these measurements offer a unique opportunity for investigation of the diurnal variation of the brightness temperatures over the Amazon rainforests. The angular distributions of brightness temperatures over the Amazon rainforest are very stable and can be simulated with a radiative transfer model, which consists of an atmospheric radiative component and a rainforest-canopy model that treats the rainforest as a uniform layer with an effective canopy temperature. The simulated results agree well with the observations. The diurnal variation of brightness temperatures over the Amazon rainforest is simulated with a Fourier-series model. It shows that a second order of Fourier series can reproduce the observed pattern of diurnal variation of the brightness temperatures at zenith angles of 0[degrees], 28.7[degrees], and 58.1[degrees], respectively. In a practical application, the coefficients of Fourier-series expansion can be used to generate the brightness temperatures as a function of diurnal hours. These results can be applied to postlaunch calibration of satellite-borne microwave radiometer with different equator crossing time. In addition, the results presented in this paper indicate that the Amazon rainforest can be used as a hot calibration reference target. The availability of a land calibration target is important for calibration and validation of spaceborne microwave radiometers. Index Terms--Advanced Microwave Sounding Unit (AMSU-A) measurements, Amazon rainforest brightness temperature, micro. wave radiometers, microwave remote sensing, satellite data.

Dense media radiative transfer (DMRT) theory is used to study the multiple-scattering effects in active microwave remote sensing. Simplified DMRT phase matrices are obtained in the 1-2 frame. The simplified expressions facilitate solutions of the DMRT equations and comparisons with other phase matrices. First-order, second-order, and full multiple-scattering solutions of the DMRT equations are obtained. To solve the DMRT equation, we decompose the diffuse intensities into Fourier series in the azimuthal direction. Each harmonic is solved by the eigen-quadrature approach. The model is applied to the active microwave remote sensing of terrestrial snow. Full multiple-scattering effects are important as the optical thickness for snow at frequencies above 10 GHz often exceed unity. The results are illustrated as a function of frequency, incidence angle, and snow depth. The results show that cross polarization for the case of densely packed spheres can be significant and can be merely 6 to 8 dB below copolarization. The magnitudes of the cross polarization are consistent with the experimental observations. The results show that the active 13.5-GHz backscattering coefficients still have significant sensitivity to snow thickness even for snow thickness exceeding 1 m. Index Terms--Active microwave remote sensing, dense media, snow.

Development of fast and accurate models of microwave devices and antennas is of paramount importance in computer-aided design and circuit analysis. At this purpose, artificial neural networks (ANNs) have been extensively exploited in technical literature. However, in the last years support vector machines (SVMs) developed by Vapnik are gaining popularity due to many attractive features capable to overcome the limitations connected to ANNs. In this work, support vector regression machines (SVRMs) modelling performances are investigated and compared with ANNs performances by means of several cases of study. Index Terms--Computer-aided design (CAD) modelling, microstrip patch antennas, microstrip radial stubs, support vector regression machines (SVRMs).

An improved finite difference time-domain formulation that can work with nonuniform internal magnetic field distributions is introduced and used to obtain the resonant frequencies of a rectangular cavity filled with magnetic material. The nonuniformity of the internal field should be considered when the applied field is of the same order as the saturation magnetization. Even in case of large applied fields, when the magnetic device is small, the deviation from uniform distribution is significant. The nonuniform internal field distribution is obtained by an iterative method, assuming that the magnetic medium is saturated in the direction of local internal field (the condition for equilibrium distribution of magnetization). It is shown that this solution is stable and satisfies the standard boundary value problem of electromagnetism. Index Terms--Cavity resonant frequencies, finite difference time-domain (FDTD) methods, magnetic microwave devices, micromagnetics.

Three-dimensional (3-D) ceramic stereolithography has been developed and used to manufacture RF devices using periodic structures. To our knowledge, it is the first time that zirconia and high-performance [Ba.sub.3]Zn[Ta.sub.2][O.sub.9] ceramics are used with that process to manufacture high unloaded quality factor resonant structures and bandpass filters working in the K a-band. A theoretical study on the performances of periodic arrangements of high-permittivity structures has been carried out and has led to the manufacture of a high unloaded quality factor cavity and narrow three-pole filter (1% bandwidth) measured at a working frequency of 33 GHz. Index Terms--[Ba.sub.3]Zn[Ta.sub.2][O.sub.9] (BZT), Bragg reflector, ceramic stereolithography process, high unloaded quality factor, narrow bandpass filter, periodic structure, 3-D ceramic technology, zirconia.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.04.012 Byline: M.J. Klein, M.D. Hofstadter Keywords: Uranus; Uranus; atmosphere; Atmospheres; dynamics; Radio observations Abstract: We present a self-consistent, 36-year record of the disk-averaged radio brightness of Uranus at wavelengths near 3.5 cm. It covers nearly half a uranian year, and includes both equatorial and polar viewing geometries (corresponding to equinox and solstice, respectively). We find large (greater than 30 K) changes over this time span. In agreement with analyses made of more limited microwave data sets, our observations suggest the changes are not caused by geometric effects alone, and that temporal variations may exist in the deep uranian troposphere down to pressures of tens of bars. Our data also support an earlier suggestion that a rapid, planetary-scale change may have occurred in late 1993 and early 1994. The seasonal record presented here will be useful for constraining dynamical models of the deep atmosphere, and for interpreting observations made during Uranus' 2007 equinox passage. As part of a multi-wavelength observing campaign for this event, the Goldstone-Apple Valley Radio Telescope (GAVRT) project will continue to make frequent, single-dish observations near 3.5 cm. Author Affiliation: Jet Propulsion Laboratory, Mail Stop 303-401, 4800 Oak Grove Drive, Pasadena, CA 91109, USA Article History: Received 26 August 2005; Revised 10 April 2006

This paper examines the broadband distortion behavior in flexible filters employing varactor-diode tuning elements. Series- and parallel-resonant varactor-loaded transmission-lines, both commonly used in bandpass and bandstop microwave filters, are analyzed. Nonlinear Volterra-series analysis is employed to determine the second- and third-order distortion ratios dependent on the frequencies of the incident signals. It is shown that in a bandpass filter (employing parallel tuned resonators), maximum distortion occurs in the passband, while in a bandstop filter (employing series tuned resonators), minimum distortion occurs at the minimum-loss passband. The analysis is verified by practical measurement of filters employing the two modes of resonators. Index Terms--Distortion, microwave filters, tunable filters.

Precipitation estimation from satellite passive microwave radiometer observations is a problem that does not have a unique solution that is insensitive to errors in the input data. Traditionally, to make this problem well posed, a priori information derived from physical models or independent, high-quality observations is incorporated into the solution. In the present study, a database of precipitation profiles and associated brightness temperatures is constructed to serve as a priori information in a passive microwave radiometer algorithm. The precipitation profiles are derived from a Tropical Rainfall Measuring Mission (TRMM) combined radar--radiometer algorithm, and the brightness temperatures are TRMM Microwave Imager (TMI) observed. Because the observed brightness temperatures are consistent with those derived from a radiative transfer model embedded in the combined algorithm, the precipitation--brightness temperature database is considered to be physically consistent. The database examined here is derived from the analysis of a month-long record of TRMM data that yields more than a million profiles of precipitation and associated brightness temperatures. These profiles are clustered into a tractable number of classes based on the local sea surface temperature, a radiometer-based estimate of the echo-top height (the height beyond which the reflectivity drops below 17 dBZ), and brightness temperature principal components. For each class, the mean precipitation profile, brightness temperature principal components, and probability of occurrence are determined. The precipitation--brightness temperature database supports a radiometer-only algorithm that incorporates a Bayesian estimation methodology. In the Bayesian framework, precipitation estimates are weighted averages of the mean precipitation values corresponding to the classes in the database, with the weights being determined according to the similarity between the observed brightness temperature principal components and the brightness temperature principal components of the classes. Because the classes are stratified by the sea surface temperature and the echo-top-height estimator, the number of classes that are considered for retrieval is significantly smaller than the total number of classes, making the algorithm computationally efficient. The radiometer-only algorithm is applied to TMI observations, and precipitation estimates are compared with combined TRMM precipitation radar (PR)--TMI reference estimates. The TMI-only algorithm, supported by the empirically derived database, produces estimates that are more consistent with the reference values than the precipitation estimates from the version-6 TRMM facility TMI algorithm. Cloud-resolving model simulations are used to assign a latent heating profile to each precipitation profile in the empirically derived database, making it possible to estimate latent heating using the radiometer-only algorithm. Although the evaluation of latent heating estimates in this study is preliminary, because realistic conditional probability distribution functions are attached to latent heating structures in the algorithm's database, a generally positive impact on latent heating estimation from passive microwave observations is expected.

Microwave observations made at the third and fourth Stokes parameters can be used to determine the surface wind direction over oceans. However, due to their smaller amplitudes (less than 3 K at the third Stokes parameter and 1 K at the fourth Stokes parameter), the absolute calibration to these measurements becomes crucial. A new methodology is developed in this study to calibrate the Windsat third and fourth Stokes parameters through tropical rain forest measurements over the Amazon and central Africa. It is found that the Windsat fourth Stokes parameter at 18 GHz has biases of the order of 0.5 K, which could severely affect the wind vector retrievals. OCIS codes: 010.0010, 120.0120, 280.0280.

We present a comprehensive microwave design framework for implementing the original, aggressive, implicit, and response residual space-mapping (SM) approaches through widely available software. General steps and tools for possible SM implementations are elaborated. Our presentation is a reference guide for microwave designers using the SM technique. An instructive 'multiple cheese-cutting' example demonstrates the SM approach to engineering design and some possible pitfalls. For the first time, an ADS framework implements the SM steps interactively. A three-section transformer example illustrates the approach, step by step. A six-section H-plane waveguide filter design emerges after four iterations, using the implicit SM and the response-residual space-mapping (RRSM) optimization entirely within the design framework. An RRSM surrogate is developed to match the fine (HFSS) model. We use sparse frequency sweeps and do not require Jacobians of the fine model. Index Terms--Computer-aided design (CAD), engineering optimization, filter design, parameter extraction (PE), space mapping (SM), surrogate modeling.

We justify and elaborate in detail on a powerful new optimization algorithm that combines space mapping (SM) with a novel output SM. In a handful of fine-model evaluations, it delivers for the first time the accuracy expected from classical direct optimization using sequential linear programming. Our new method employs a space-mapping-based interpolating surrogate (SMIS) framework that aims at locally matching the surrogate with the fine model. Accuracy and convergence properties are demonstrated using a seven-section capacitively loaded impedance transformer. In comparing our algorithm with major minimax optimization algorithms, the SMIS algorithm yields the same minimax solution within an error of [10.sup.-15] as the Hald-Madsen algorithm. A highly optimized six-section H-plane waveguide filter design emerges after only four HFSS electromagnetic simulations, excluding necessary Jacobian estimations, using our algorithm with sparse frequency sweeps. Index Terms--Computer-aided design (CAD) algorithms, electromagnetics, filter design, interpolating surrogate, microwave modeling, optimization, output space mapping (OSM), space mapping (SM), surrogate modeling.

Recently, Teo et al. proposed a discrete complex image method that is able to represent both the near and far fields of the Green's function accurately, using only a single approximate Green's function. In this paper, an error analysis of this method is presented. The error analysis shows an additional term, which represents the quasi-static image of the surface-wave poles plays a crucial role in the convergence and accuracy of this new method. As the extraction of poles is required, a recently proposed algorithm by Teo et al. is also discussed and compared with existing methods in terms of computational speed. Index Terms--Discrete complex image method (DCIM), discrete complex image, Green's function, proper poles, Sommerfeld transform, surface-wave poles.

A system theory approach for the modeling of colored noise sources in devices and circuits driven in large-signal (LS) conditions is discussed. The order of the modulation and filtering steps resulted in two different LS noise sources.

The measurement of the source reflection coefficient is fundamental for noise, as well as large-signal testing of microwave active devices. This paper describes a simple yet rigorous technique for fast and accurate determination of a source reflection coefficient when a load-source pull test set is used. The solution consists in measuring the waves at the device-under-test reference plane under two different bias conditions. We have proven that these measurements give enough information to compute the source reflection coefficient with accuracy suitable for most applications. Experimental results are presented and compared to data obtained with more conventional techniques. Index Terms--Active device characterization, error box, microwave measurements, network analyzer calibration, source impedance, source--pull, source reflection coefficient.

An analytical study compared a high temperature superconducting microstrip filter and its gold counterpart with respect to insertion loss, transmission characteristics, bandwidth and other attributes. It was found that the high temperature superconducting filter used in the experiment holds a lot of promise for high efficiency communications systems. Design technique, filter fabrication, experimental arrangements, findings and conclusions are presented.

A study evaluated a number of high temperature, superconducting, thin film, passive, microwave components for new generation mobile communication systems. These devices include miniature resonators, narrow-band bandpass filters, bandstop filters, tandem couplers and duplexers. They were designed within the context of full-wave electromagnetic simulations and fabricated using yttrium barium copper oxide thin films on either MgO or LAO substrates.

A microwave diversity imaging system conventionally uses a vector network analyzer (VNA) to directly measure the object scattered field (amplitude and phase) over a selected frequency range and viewing angles, then reconstructs the scattering object characteristic function through two-dimensional Fourier inversion. In this paper, we present a cost-effective microwave diversity imaging system using a six-port reflectometer, which measures four amplitude (or power) values to acquire the object scattered field indirectly. One can then eliminate the coherent detectors in a VNA. The calibration procedure for this microwave diversity imaging measurement is also described. Experimental results of three types of scattering objects, a metallic cylinder, four distributed line scatterers, and a 72:1 scaled B-52 aircraft model, are presented using the described six-port microwave imaging system. Index Terms - Microwave diversity imaging, six-port reflectometer.

Procedures to calibrate network analyzers using unknown calibration lines and series impedances are presented. These LZY and LZN self-calibration procedures are specifically suited for measurements on planar and integrated circuits. By means of the self-calibration algorithm, the propagation constant of the line standards and the quantities of the reflection standards Y and N are determined. The LZN procedure requires three two-port standards, whereas the LZY procedure deals with two standards only. The fact that it is neither necessary nor advisable to know all standards completely allows the realization of the planar calibration standards in an easy way. Both self-calibration procedures according to the seven-term model are based on closed mathematical solutions so that the accuracies are good, as demonstrated by measurement results. Index Terms - Calibration of a network analyzer, de-embedding, microwave device and on-wafer measurements.

The fast Hankel transform (FHT) algorithm is implemented in the mixed-potential integral-equation (MPIE) analysis of planar microstrip circuits in stratified media. The spatial-domain Green's functions are accurately and quickly obtained by applying the FHT algorithm to the exact spectral-domain counterparts. Therefore, the entire analysis procedure has high accuracy and efficiency. A nonuniform partition scheme is used to effectively model the rapid change of current distributions around discontinuities. A generalized supplementary equation accounting for arbitrary termination conditions at both feeding and load ends is also derived. The proposed method is used to design a single-stub band-stop filter and a compensated dc block circuit. Experimental measurements are performed to validate the computation. Index Terms - Fast Hankel transform, microstrip discontinuities, mixed-potential integral-equation method.

A study was presented to analyze the design of the depressed collector system and the scheme for high-voltage gyroklystron amplifiers. The net efficiency of the gyroklystron design was also analyzed. Results revealed that the design of the gyroklystron amplifiers can be improved from 41.1% to 54.8% by recovering 42.4% of the spent beam energy. In addition, energy recovery using the single-stage depressed collector can be utilized for a high-power, pulsed device.

In this paper, a new design for the gap used as an optically controlled microwave switch is proposed. This new design is based on the use of a rib structure in the gap region. The proposed structure is studied using the finite-difference method (FDM). Obtained results show that for small gaplengths, the structure figure of merit, defined as the product of the ON/OFF ratio and the bandwidth, can be improved by about 38 dB * GHz. Index Terms - Gap, optically controlled, rib structure.