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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.

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).

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.

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.

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.

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.

Landslides in Malaysia, and other tropical countries where heavy monsoon rains are common, form a risk to people, buildings, and roads. In particular, steep slopes that have been cut to accommodate road lines are prone to landslides. The objective of the study was to develop algorithms and methods that can be used to alert on increased risk of landslides through detecting small signs of slope instability with synthetic aperture radar (SAR) image analysis. A time series of 19 scenes from the TerraSAR-X satellite was analyzed in study site Gunung Pass. Amplitude image analysis and interferometric techniques were applied to study soil movements. Two terrace fragments were measured to have slid 2.5 and 4.9 m in two amplitude images. The phase of topography-flattened coherence images was used to map small movements in a slope-failure area. The highest movement that was detected with interferometric techniques was 1.71 cm while the corresponding movement in ground data was 2.65 cm. High soil movements (over 16 cm) in the slope failure area prevented the use of phase data because fringes disappeared. [ABSTRACT FROM PUBLISHER]