Study On Tri-reflector Compact Antenna Test Range At Millimeter And Sub-millimeter Bands

Millimeter and sub-millimeter technology are widely used in many applications, such as meteorology, radio astronomy, civil security, and so on. Usually, antenna sub-system plays a vital role in the whole system.To ensure the performance of the antenna system, accurate pattern measurement should be carried out. However, the measurement of electrically large antenna system at such a high frequency is a challenging task. Compact Antenna Test Range (CATR) can generate a pseudo-plane wave field, usually referred as Quiet Zone (QZ), for the antenna measurment in a range. At the millimeter and sub-millimeter bands,CATR is one of the most promising methods for the electrically large antenna measurementIn this thesis, studies on the design, measurement and application of CATR are carried out. A tri-reflector CATR demonstrator is accomplished, and the design for tri-reflector CATR with high cross-polarization isolation is also completed, which can be used as a guideline for the implementation of the next generation of tri-reflector CATR.First of all, a ray-tracing based reflector shaping procedure for the aperture field synthesis is developed. With this method, a Cassegrain-Gregorian (CG) tri-reflector CATR is designed. Two shaped sub-reflectors, which are considerably smaller than the main reflector, are used to correct the pattern emitted by the feed and obtain the desired aperture field with high quiet zone usage. From the simulated results, the QZ performance with the peak to peak amplitude (phase) ripple within 1 dB (10 deg), and the cross-polarization isolation more than 30 dB is achieved. Besides, the nonredundant sampling strategy based on the spatially band-limited properties of the scattered fields and the optimal sampling interpolation (OSI) formula is adopted to evaluate the QZ performance of CATR. Numerical results show that the required sampling interval is much larger than the classical half wave-length interval.Secondly, the sine-squared/linear dual profile corrugated horn with low side-lobe is designed as the feed of the CG tri-reflector CATR. The analysis for the focal region field of the designed tri-reflector CATR has been carried out, showing that the cross-polarization field of the system can be compensated by the higher order asymmetric waveguide mode HE21 in a properly designed corrugated horn. Then two novel tri-mode corrugated matched horns are designed, and the cross-polarization component in the CG tri-reflector CATR can be effectively cancelled.Thirdly, the study on the effective measurement of the aperture antennas at millimeter and sub-millimeter bands have been carried out.The pattern of a corrugated horn working at F band is measured with the planar near field measurement. Then a far-field antenna test range is built-up and the corrugated horns working at higher frequencies are measured. The co-polarization fields of the CG tri-reflector CATR demonstrator are also measured with planar near field measuement. After data post-processing, the measured QZ fields at 193 GHz and 290 GHz show that the amplitude (phase) ripple within 1.5 dB (20 deg) are obtained in the two-dimensional QZ field. The ability of this demonstrator has been also unveiled by the mesaurement of a corrugated horn with known pattern at sub-millimeter band.Lastly, an offset tri-reflector configuration based on the paraboloid main reflector is proposed to fulfill a tri-reflector CATR with high cross-polarizaiton isolation. Here the high cross-polarization isolation is enforced by the initial system configuration without any strategy used to control the cross-polarization in the shaping procedure. Then two tri-reflector CATR systems with paraboloid main reflector are synthesized. From the simulation results, the QZ performance with the peak to peak amplitude (phase) ripple within 1 dB (10 deg), and the cross-polarization isolation more than 40 dB is achieved. These provide a guideline to implement a tri-reflector CATR with high cross-polarizaiton isolation for the measurement of electrically large antennas at millimeter and sub-millimeter bands.