Two high-gain terahertz (THz) offset reflector antennas are proposed. The silicon carbide material and thermally stable carbon fiber-reinforced plastic are selected as reflectors for high specific stiffness and low thermal expansion coefficient which are helpful for space use. Dual polarization is achieved by introducing a wire-grid polarizer which can separate the two THz polarization waves provided by multimode horns fabricated in electroforming technology. Furthermore, three-coordinate test system and theodolites are employed to detect the surface error of dishes and alignment of antenna subsystem. The physical optics analysis based on the measured reflector surface data is introduced referring to the large aperture antenna patterns by virtue of its accuracy and high efficiency. The results of this novel method are compared to that of the near-field test. Measurements show that the sidelobe levels (SLLs) of the single polarization silicon-based reflector are below −32 dB while the gain is 55.3 dB at 330 GHz, and the dual polarization carbon fiber-reinforced plastic reflector antenna suppresses the SLLs to −28 and −29 dB in two principal planes while the gain is 57.2 dB at the same frequency, respectively. The good performances of the proposed antennas indicate the potential for the application of space THz radiometer.

Terahertz High-Gain Offset Reflector Antennas Using SiC and CFRP Material

A backpropagation technique is investigated that uses the plane wave spectrum to reconstruct the subwavelength features of the current distribution on flat surfaces without damaging the surface under measurement. The technique employs spectral and spatial filtering of the measured signal to capture the propagating spectrum as well as a portion of the evanescent spectrum. Special consideration is given to avoiding exponential amplification of measurement noise during backpropagation of the evanescent spectrum. This approach uses equipment commonly available in antenna measurement laboratories, for example, a network analyzer, a horn antenna, a magnetic field probe, and an automated positioning apparatus for the probe. The approach is first studied using computer simulations. The results from the simulations are then used as a guide to develop an actual measurement system. The measurement system is constructed and tested by measuring the surface current on a slotted plate. The measured current distributions are compared with results from finite-difference time-domain (FDTD) computations to demonstrate the feasibility of the technique.

A system for unobtrusive measurement of surface currents

Using a near-field antenna measurement facility, it is possible to simultaneously evaluate the surface accuracy of a reflector antenna as well as the far-field pattern of the antenna for a short time. The surface errors of a 2-m deployable mesh reflector for satellite use were measured by a planar near-field system. As a result, the influence of periodic structures, due to the antenna ribs, is clearly observed. Also, the surface accuracy obtained with the near field scanning technique coincides well with that obtained by an optical measurement technique. >

Surface accuracy measurement of a deployable mesh reflector by planar near-field scanning

For a compact range (CR), the near-field angular spectrum can be obtained by making an inverse Fourier transform of its aperture spatial near field. The characteristics of the aperture design have been carried by the aperture near-field angular spectrum. The direct wave and edge-diffracted waves from the aperture can be separated and distinguished clearly in the angular domain. Therefore, the CR performance can be evaluated and improved accordingly. In this paper, based on the aperture field convolution method and plane wave spectrum (PWS) theory, near-field angular spectrums for different apertures have been computed. The general criteria for the CR aperture design have been discussed. The selections of the whole aperture shape, the serration height, the serration base length, the serration number, and the serration shape (including isosceles and right-angled triangles) have been compared. At last, the near fields of an optimized serrated-edge aperture and an original circular aperture in different transverse planes have been computed and compared. The width and height of the apertures are all 30 wavelengths in free space. In order to suppress the sidelobes, a Chebyshev window with ${- 50} $ dB sidelobes has been adopted in the spatial-angular transform.

Compact Range Performance Evaluation Using Aperture Near-Field Angular Spectrums

The authors demonstrate an approach that is an effective, noninvasive means of measuring surface current distributions Some guidelines for making the measurements are given, and results from an actual measurement are presented For example, it is shown that the magnetic field components have better measurement characteristics than the electric field components The number of spatial samples per wavelength can be estimated from the spatial sharpness of the current distribution The size of the measurement window, which is directly proportional to the measurement distance, must be sufficiently large to capture the majority of the spatial field distribution and to prevent the edges of the window from interfering with the results In addition, the extraction of sub-wavelength features or sharp edges requires the measurement plane to be close to the surface current, a high SNR, close spacing of measurement samples, and a small field probe

http://ieeexplore.ieee.org/iel6/8259/25865/01150098.pdf

A measurement of surface accuracy of deployable mesh reflector by planar near-field scanning

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Surface accuracy measurement of a deployable mesh reflector by planar near-field scanning

A measurement of surface accuracy of deployable mesh reflector by planar near-field scanning