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A hologram-based compact antenna test range (CATR) is designed, constructed, and used to test a 1.5-m antenna at 650 GHz. The CATR is based on a 3.16-m-diameter hologram as the collimating element. So far, this is the highest frequency at which any CATR has been used for antenna tests. The quiet zone is measured and optimized before the antenna tests. The measured antenna pattern results at 650 GHz are analyzed and compared to the simulated patterns. Feed scanning antenna pattern comparison technique is used to correct the antenna pattern. These tests show the hologram CATR to be promising for antenna measurements up to 650 GHz. Index Terms--Antenna measurements, compact antenna test range (CATR), computer-generated hologram, submillimeter waves.

In this paper, propagation properties of a parallel-plate waveguide with tunable artificial impedance surfaces as sidewalls are studied both analytically and numerically. The impedance surfaces comprise an array of patches over a dielectric slab with embedded metallic vias. The tunability of surfaces is achieved with varactors. Simple design equations for tunable artificial impedance surfaces, as well as dispersion equations for the TE and TM modes are presented. The propagation properties are studied in three different regimes: multimode waveguide, single-mode waveguide, and below-cutoff waveguide. The analytical results are verified with numerical simulations. Index Terms--High-impedance surface, impedance waveguide, propagation properties, tunable.

Simple analytical formulas are introduced for the grid impedance of electrically dense arrays of square patches and for the surface impedance of high-impedance surfaces based on the dense arrays of metal strips or square patches over ground planes. Emphasis is on the oblique-incidence excitation. The approach is based on the known analytical models for strip grids combined with the approximate Babinet principle for planar grids located at a dielectric interface. Analytical expressions for the surface impedance and reflection coefficient resulting from our analysis are thoroughly verified by full-wave simulations and compared with available data in open literature for particular cases. The results can be used in the design of various antennas and microwave or millimeter wave devices which use artificial impedance surfaces and artificial magnetic conductors (reflect-array antennas, tunable phase shifters, etc.), as well as for the derivation of accurate higher-order impedance boundary conditions for artificial (high-) impedance surfaces. As an example, the propagation properties of surface waves along the high-impedance surfaces are studied. Index Terms--Analytical model, high impedance surface, oblique incidence excitation.

Transmittance and monostatic reflectivity of different radar absorbing materials at 650 GHz are presented. The reflectivity was measured in plane-wave conditions in a radar cross-section (RCS) range with vertical polarization. The lowest reflectivity level (-70 dB) was achieved with commercial absorbers TK THz RAM and Firam-500 with oblique incidence angles. Floor carpets were also studied, and the reflectivity level of those was found to be sufficiently low (from -50 to -60 dB) for use in antenna test ranges. Results agree with earlier studies and indicate the applicability of the RCS method in reflectivity measurements also at 650 GHz. Index Terms--Antenna test range, monostatic reflectivity, radar absorbing materials (RAMs), radar cross section (RCS).

An antenna pattern correction technique, is presented that is based on an adaptive array algorithm. In the method, the antenna pattern of the antenna under test (AUT) is measured several times at different positions in the quiet-zone. The corrected antenna pattern is obtained by taking a weighted average of the measured patterns. An array synthesis algorithm is employed for obtaining the averaging weights at each rotation angle of the AUT. The weights are adapted specifically for a given AUT. The adaptive array correction technique is demonstrated in a hologram based compact antenna test range (CATR) at 310 GHz with both a synthetic antenna and a physical test antenna. For verification, the accuracy provided by the adaptive array correction technique is compared to that provided by uniform weighting. Index Terms--Antenna measurements, compact range, error compensation, submillimeter wave measurements.

We present the design, simulations, fabrication, and measurements of a W-band waveguide impedance tuner. The design consists of a WR-10 waveguide with two E-plane arms for tunable dielectric-based backshorts. The impedance tuner is fabricated using a simple split-block technique and is easily scalable to submillimeter wavelengths. Our design shows an excellent input impedance range, tuning accuracy, repeatability, and a high attainable maximum reflection coefficient over the frequency band of 75-110 GHz. Our tuner applies dielectric-based backshorts, which provide a tuning accuracy better than that of other waveguide backshorts. Index Terms--Dielectric-based backshort, impedance tuner, E-plane, waveguide, W-band.

The measurement accuracy of a compact antenna test range (CATR) is limited by the level of spurious signals. At millimeter and submillimeter wavelengths the spurious signals are caused by range reflections and deformations of the range collimating element. Several antenna pattern and range evaluation techniques that can be used to mitigate the effects of these nonidealities have been published. At submillimeter wavelengths these techniques are typically time consuming or they are not able to correct the antenna pattern close to the main beam. The frequency shift technique does not have these limitations in a hologram based CATR. In this paper, the applicability of the frequency shift technique is analytically studied for a hologram based CATR. The technique is verified by measurements. The accuracy provided by the frequency shift technique is compared to that of the antenna pattern comparison (APC) technique. Index Terms--Antenna measurements, compact range, error compensation, submillimeter wave measurements.

This paper presents monostatic reflectivity measurements of radar absorbing materials at 310 GHz in a phase-hologram-based compact range. The radar cross-section method was used and the backscattered reflection was measured with horizontal and vertical polarizations in plane-wave conditions. Transmission was also studied. The reflectivity was measured over an incidence angle of 0[degrees]-45[degrees]. The reflectivity of Thomas Keating Terahertz RAM at normal incidence was found to be -56 dB--the smallest of the studied materials. The reflectivity of carpet material measured was also below -40 dB and it was found to be suitable for use as an absorber. The results are in line with those available from previous studies of reflectivity and complement them with new materials, frequency, and angle information. Index Terms--Compact range, monostatic reflectivity, radar absorbing materials, radar cross-section (RCS) method.

A compact radar cross section (RCS) test range based on a phase hologram has been developed for scale-model measurements. The phase hologram converts the feed-horn radiation to a plane wave needed for RCS determination. The measurements are performed at 310 GHz using continuous-wave operation. A monostatic configuration is realized using a dielectric slab as a directional coupler. The main advantage of a scale-model RCS range is that the dimensions of radar targets are scaled down in proportion to the wavelength. Therefore, RCS data of originally large objects can be measured indoors in a controlled environment. Test objects such as metal cylinders and simplified targets have been measured. The feasibility of the phase-hologram RCS range has been verified. The operation and measurement results of the monostatic measurement range are reported here. A comparison with simulated results is also included. Index Terms--Compact range, hologram, quiet zone, radar cross section (RCS), scale-model measurements.

Manufacturing of large computer-generated submillimeter wave holograms with high pattern accuracy has been the main challenge in the development of hologram based compact antenna test ranges (CATRs). Illumination of the hologram with a shaped beam produced by a dual reflector feed system (DRFS) simplifies the hologram manufacturing by eliminating the narrow slots in the hologram pattern. In this paper, the design of a shaped dual reflector feed for a hologram CATR is described. The simulated and measured illumination field amplitude and phase at 310 GHz are presented and compared to the desired hologram illumination. The measured amplitude is within [+ or-] 0.5 dB from the design objective in the most significant central region of the illuminating beam. Measurement results of the quiet-zone field of a demonstration CATR illuminated by the DRFS are presented and compared to the measured quiet-zone amplitude and phase of a hologram fed directly with a corrugated horn. The quiet-zone diameters of the both holograms are over 0.25 meters and the measured root mean squared (rms) amplitude and phase ripples are below [+ or -] 0.4 dB and [+ or -] 5[degrees], respectively. Further improvements to the hologram CATR, such as greater tolerance to manufacturing errors, are also discussed. Index Terms--Compact range, computer-generated hologram, multireflector antennas, submillimeter wave antennas.

A hologram-based compact antenna test range (CATR) is being developed to overcome challenges met in antenna testing at submillimeter wavelengths. For the first time, this type of CATR has been built for testing of a large reflector antenna at submillimeter wavelengths. The CATR is based on a 3-m computer-generated hologram as the focusing element. This paper discusses the design and the construction of the CATR, and the verification of the CATR operation with quiet-zone tests done for the CATR prior to the antenna testing. Assembly of the CATR, testing of the 1.5-m reflector antenna at 322 GHz, and the disassembly were all done within two months in 2003. The quiet-zone field measurement results are analyzed in this paper. The CATR was concluded to be qualified for antenna testing. The antenna testing is described in a separate paper. Index Terms--Antenna measurements, compact antenna test range (CATR), computer-generated hologram, submillimeter wave.

The measurement accuracy of a compact antenna test range (CATR) depends on the level of spurious signals. To improve the measurement accuracy, several error compensation methods have been developed, but most of them are not feasible at submillimeter wavelengths. This paper introduces an error compensation technique for compact antenna test ranges, which is especially suitable at submillimeter wavelengths. The method is based on antenna pattern comparison (APC). In the original APC technique the antenna pattern is recorded several times at different positions of the quiet-zone field, and the corrected pattern is obtained by averaging the measured patterns. In the proposed method, the lightweight transmitter is moved instead of moving the heavy combination of the antenna under test (AUT) and the rotation stage. The feasibility of the method is studied and the method is tested with measurements in a hologram based compact antenna test range at 310 GHz. The accuracy provided by the proposed method is compared to the accuracy provided by the conventional APC. The accuracies provided by both methods are practically equal. Index Terms--Antenna measurements, compact range, error compensation, submillimeter wave measurements.

Hologram-based compact antenna test range (CATR) is a potential method for testing large antennas at submillimeter wavelengths. This paper describes testing of a 1.5-m single offset parabolic reflector antenna with a 3-m-diameter hologram-based CATR. This is the first time such a measurement is carried out at submillimeter wavelengths. The antenna tests were done in a CATR that was specifically designed and constructed for these tests. The measured radiation pattern at the frequency of 322 GHz is presented. The measured pattern corresponds reasonably well to the simulated pattern of the antenna. The effect of the quiet-zone field nonidealities on the measurement results and the reasons for the discrepancies in the measured antenna beam are discussed. Index Terms--Antenna measurements, compact antenna test range (CATR), hologram, submillimeter wave antennas.

This paper studies the feasibility of a hologram-based compact antenna test range (CATR) for submillimeter-wave frequencies. In the CATR, a hologram is used as a collimating element to form a plane wave for antenna testing. The hologram is a computer-generated interference pattern etched on a thin metal-plated dielectric film. Two demonstration holograms of approximately 1 m in diameter were designed for 650 GHz, and they were manufactured on two different Mylar films. The holograms were illuminated with a horn, and the plane-wave field was probed at 644 GHz. The measured amplitude and phase ripples were 2 dB and 15[degrees] peak-to-peak for one of the holograms. A higher quiet-zone field quality can be achieved by increasing the manufacturing accuracy by further manufacturing tests. After this, the hologram-based CATR should have a potential for high-quality antenna tests at frequencies up to 650 GHz. Index Terms--Antenna measurements, compact antenna test range (CATR), hologram, submillimeter wave.

Passive intermodulation (PIM) distortion is a challenging problem in the design and manufacturing of base station antennas. Small nonlinearities, typically in junctions, may cause a distortion signal that interferes with the receiver even with a level of--155 dBc in a GSM900 system. The PIM level specification of an outdoor base station antenna is difficult to achieve and the sources of PIM generation are laborious to track down. In this paper, a near-field measurement method is presented to localize and investigate passive intermodulation sources in antennas and open transmission lines. The principle of the PIM near-field measurement is otherwise the same as in a common reactive near-field measurement, but instead of measuring the signal at the input frequency, the signal amplitude and phase at the PIM frequency of interest are acquired. The constructed measurement system is capable of measuring PIM signal levels down to--110 dBm with 2 x 43 dBm transmit power in the GSM900 frequency band. As demonstration measurements, PIM sources in a two-element base station antenna and in a microstrip line are localized. Index Terms: Base station antenna, near-field measurement, passive intermodulation, sensitivity.

A new coplanar waveguide (CPW)-to-rectangular waveguide transition is proposed for wide-band millimeter-wave applications. The transition has an in-line structure, which provides easy fabrication of the CPW circuit and waveguide block. An X-band (8.2-12.4 GHz) model has been designed and tested. Measurements of a back-to-back double transition have yielded a return loss of over 17 dB and an insertion loss of less than 0.5 dB over the full X-band. These results agree well with the simulated results obtained with a commercial electromagnetic structure simulator. In addition, this type of a transition has been designed and used for a local oscillator feed with a full F-band (90-140 GHz) coverage of a submillimeter-wave general-purpose harmonic mixer. Index Terms--Coplanar waveguide (CPW), millimeter wave, rectangular waveguide, transition, wide-band.

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.

An microwave activities and infrastructures in Europe is presented. The material is organized in 17 sections, each devoted to a country or group of countries and prepared by an internationally renowned microwave expert. In general, each section contains some history of microwaves in the region, and highlights some microwave activities in association with research centers, laboratories and institutions, industry, education, and national conferences. Index Terms--Austria, Balkan, Baltic, Belgium, Czech, Denmark, Europe, Finland, France, Germany, Hungary, Ireland, Israel, Italy, microwave industry, microwave professional societies, microwave research, microwave technology, microwaves, Poland, Portugal, Russia, Slovak, Spain, Sweden, Switzerland, The Netherlands, U.K.

In this paper, an efficient three.dimensional finite-difference time-domain (FDTD) approach based on the D-, E-, and H-fields is proposed to handle arbitrary anisotropic dielectric media; and, particularly, the way of imposing the electric-wall boundary condition on the surface of perfect electric conductors is discussed in details. By combining the proposed FDTD approach with the material-independent perfectly matched-layer absorbers, the performance of a line-fed microstrip patch antenna deposited on general anisotropic dielectric substrate is investigated. The scattering parameters of the antenna as a function of the rotation angle of the optical axis of the anisotropic substrate are presented for the first time. Numerical results demonstrate how the resonant frequencies of the antenna are influenced by the anisotropy. Index Terms - FDTD, general anisotropic dielectric media, MIPML absorber, patch antennas.

A low-profile high-gain antenna array of box horns for the frequency band 57.2-58.2 GHz is presented. The antenna consists of 256 radiating elements divided into two subgroups of 128 elements fed by a rectangular waveguide feed network. The radiating elements are fed in parallel and the waveguides are connected with T-junctions. The matching of the T-junctions is improved with a matching pin and a splitter. Because of the waveguide feed network, the element spacing is larger than one wavelength, which causes grating lobes. The grating lobes and sidelobes in the H-plane have been suppressed by the use of a combination of subarrays, a special characteristic of the box horn, and an array amplitude tapering. The measured sidelobe levels in the H-plane are below -30 dB at angles larger than 8 [degrees] from boresight. A gain higher than 35.7 dBi and a return loss higher than 14.4 dB have been measured for the antenna over the band 57.2-58.2 GHz. Index Terms - Grating lobes, horn antenna, millimeter-wave antenna arrays.

A tunerless cryogenic millimeter-wave ring filter has been designed for a space application. Detuning of the center frequency caused by thermal deformations has been compensated by a novel mechanism based on the use of two materials with different temperature expansion coefficients. An improvement of 1:8 in the detuning of the center frequency, compared to an uncompensated ring filter, is reported. By applying the new design, external tuning aids can be avoided even in applications where a wide operational temperature range is of interest. Thus, the new ring filter is especially advantageous in space-borne millimeter-wave receivers. Index Terms - Diplexer, ring filter, space application, temperature compensation.

A planar antenna in which box horns are used as radiating elements is described. The feed network is built by connecting rectangular waveguides with T-junctions. The matching of the T-junctions is improved by using rounded splitters and matching pins in the junctions. The radiating element has been designed to cancel out the grating lobe. The grating lobe is due to an element spacing larger than one wavelength. The highest sidelobes are at least 31 dB below the main beam in the H-plane and 16 dB in the E-plane. A gain of 37 dBi has been achieved at 39.2 GHz. These results demonstrate the feasibility of this antenna for applications requiring high gain at millimeter wavelengths. Index Terms - Antenna arrays, horn antennas, millimeter wave, planar antenna.

The application of conventional reflector-type compact antenna test ranges (CATR's) becomes increasingly difficult above 100 GHz. The main problems are the tight surface accuracy requirements for the reflectors and, therefore, the high manufacturing costs. These problems can be overcome by the use of a hologram type of compact range in which a planar hologram structure is used as a collimating element. This idea is described and its performance is studied with theoretical analyses and measurements at 119 GHz. Index Terms - Antenna measurements.

Through the study of the step recovery diode (SRD) models, a method for improving the efficiency of CAD of SRD frequency multipliers is proposed. By reducing the nonlinearity of the SRD model to an appropriate extent, the simulation and optimization of SRD frequency multipliers can be carried out more easily and faster. Systematic design and optimization of an SRD frequency multiplier is described. Simulation results of this SRD frequency multiplier are compared with experimental results.

Most frequency multipliers at submillimeter wavelengths are based on the Schottky varactor. The main problem of these multipliers is the output power, which remains low at frequencies above 500 GHz. The aim of this work is to help the situation by studying the usability of the conventional equivalent circuit during a fast voltage modulation. The anode edge effects play an important role in this voltage modulation. While the fringing fields, due to the edge effects, reduce the capacitance modulation in small submillimeter-wave varactors, the edge effects also lessen the effect of electron velocity saturation compared with an ideal varactor with a pure parallel plate capacitance. The usefulness of the static model can be estimated by comparing the three-dimensional shape of the depletion layer to the shape given by the dynamic model. The dynamic shape can be obtained by solving the potential and electron conduction currents in the epitaxial layer of the Schottky varactor. In this work the potential and the electron currents have been calculated from simplified device physics by using numerical methods.

A simple, efficient, and unified source excitation scheme for the finite-difference time-domain (FDTD) analysis of both waveguides and microstrip circuits is developed and validated. In this scheme, by moving the source plane several cells inside the terminal plane and adding the excitation wave as an extra term in the FDTD equation, the interaction between the excitation and reflected waves are totally separated in time domain. Hence, for both waveguide and microstrip discontinuities, absorbing boundary conditions can be applied on the terminal plane directly. In particular, for microstrip circuits, our scheme does not induce any source distortions when a simplified field distribution is used as the excitation. Consequently, the terminal plane can be moved very close to the discontinuity and thus significant computational savings are achieved. In addition, for microstrip systems, the validity and efficiency of the Mei's simplified field distribution are evaluated and confirmed for the first time.

The back-to-back barrier-N-[N.sup.+] (bbBNN) varactor is a nonlinear device being developed for frequency multiplier applications above 100 GHz. Its symmetrical C-V characteristic, low series resistance, freedom from external bias and suitability to planarization make it an ideal choice for high frequency, low power, odd harmonic generation. In this paper, the performance of a 220-GHz waveguide tripler using, for the first time, a planar GaAs bbBNN device integrated on a quartz microstrip circuit is presented. A new split-waveguide block design has been employed to provide the proper embedding impedances to the device at the input and third harmonic output frequencies. A flange-to-flange tripling efficiency of 7% has been obtained at 220 GHz with an output power in excess of 700 [micron]W. This is believed to be the highest conversion efficiency yet reported for a tripler with an integrated device at this frequency. Theoretical calculations indicate that substantial improvement is possible with modest changes to the device and circuit parameters.

Schottky varactor frequency multipliers are used to generate local oscillator power at millimeter and submillimeter wavelengths. The equivalent circuit of the Schottky varactor contains a junction capacitance, a junction conductance, a series resistance and a model for electron velocity saturation. At millimeter wavelengths the equivalent circuit is affected by the edge effects, which are due to the small-area circular anode. The correction factors due to the edge effect for the junction capacitance and for the series resistance are available in the literature. In this work the electron velocity saturation is modeled by limiting the velocity of the transition front between the depleted and undepleted layer. By using this model the maximum current of the diode is given by the actual area of the transition front between depleted and undepleted layers, and is therefore related to the capacitance correction factor. The new model has been tested by analyzing a two diode balanced doubler for 160 GHz presented earlier in the literature. The agreement between the theoretical results and the measurements is excellent. The new diode model is useful in optimization of varactors for high millimeter and submillimeter wave frequencies.

InGaAs/InAlAs single-barrier varactor (SBV) diodes are tested as frequency quintuplers. The diodes were tested in a crossed-waveguide structure and provided output frequencies between 148 and 187 GHz. The highest observed flange-to-flange efficiency was 0.78% at an output frequency of 172 GHz. This is nearly four times greater than the best quintupler efficiency obtained for previous SBV varactors made from the GaAs/AlGaAs materials system.

This paper describes the performance of planar back-to-back Barrier-N-N+ (bbBNN) devices for frequency multiplier applications. A tripling efficiency of 3.3% has been achieved using these devices in a 200 GHz crossed waveguide mount. This is the first experimental result with a bbBNN waveguide frequency multiplier. A technique has been developed for characterizing planar bbBNN devices with a network analyzer, which gives both the series resistance and voltage dependent capacitance of the device. The experimental results are compared with the theoretical multiplier performance, calculated using a large signal analysis approach.

The efficiency of a Schottky varactor frequency multiplier at submillimeter wavelengths can be increased by cooling the diode. The main reason for better efficiency is the increased mobility of the free carriers. Because of that the series resistance decreases and the efficiency can be expected to increase as much as a few dB at low input power levels. At high output frequencies and at high power levels the efficiency of the multiplication is decreased by the current saturation, because the junction capacitance cannot be pumped effectively. When the diode is cooled the maximum current of the diode increases and much more output power can be expected. There are also slight changes in the I -V characteristic and in the diode junction capacitance, but they have a negligible effect on the efficiency of the multiplier. The theoretical maximum output power at near 1 THz is calculated to increase by about 10 dB from 50 microns W to 500 microns W, when the multiplier chain is cooled to 77 K. However, cooling to 77 K is not necessary, because considerable improvement in the efficiency may be achieved by cooling to 150 K, readily available in space by passive cooling.

At millimeter-waves quasi-optical systems are commonly designed based on the Gaussian beam and thin lens approximation. The accuracy of the Gaussian beam and thin lens approximation was studied in the case of a corrugated horn and a thick Teflon lens (f / D = 1.2) combination at 87 GHz. A special near-field measurement system was constructed. A large disagreement between the measured and theoretical values with the approximative method was obtained. In particular, the measurements showed that the thin lens approximation breaks down, when the distance from the input beam waist to the lens is less than 1.5 D. Theoretical values obtained with a thick lens model based on ray tracing and use of exact Huygens' aperture integration principle agree well with the measurements.

Marcatili's method for the calculation of rectangular dielectric rod waveguides has been modified for uniaxial anisotropic dielectric materials. The averaging method without guessing the field distribution has been used to derive the equations. Experimental results for an anisotropic sapphire waveguide show a good agreement with those calculated using the approach developed here. Index Terms--Marcatili's method, rectangular dielectric waveguide, uniaxial anisotropic sapphire waveguide.