Development of Characterization Methods for Antennas and Quasi- Optics

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Zhou Du Name of the doctoral dissertation Development of Characterization Methods for Antennas and Quasi-Optics Publisher School of Electrical Engineering Unit Department of Radio Science and Engineering Series Aalto University publication series DOCTORAL DISSERTATIONS 8/2015 Field of research Radio Engineering Manuscript submitted 16 September 2014 Date of the defence 30 January 2015 Permission to publish granted (date) 26 November 2014 Language English Monograph Article dissertation (summary + original articles) Abstract This dissertation focuses on the development of characterization methods for antennas and quasi-optical components. The dissertation presents three new methods to deal with certain limitations occurred during the antenna measurement processes. First, a new technique using the Chebyshev polynomials has been proposed to process the antenna measurements obtained in non-anechoic sites to obtain equivalent free space radiation patterns. This new technique combines the principle of a FFT-based method with the special relationship between coefficients of the BesselChebyshev polynomials. Experimental results are presented to demonstrate the potential of this approach over conventional time gating techniques for a certain class of problems. Second, a new antenna pattern retrieval method is proposed. In this method, the antenna reflection coefficient is measured many times when a unique reflective load with known spatial reflection properties is placed near the antenna in each measurement. The antenna pattern is obtained from the measurements with an inversion algorithm. Simulations have been used to verify the theoretical basis and the method has been experimentally demonstrated at 30 GHz. The results show that the method could enable sufficient accuracy with low gain antennas or in the vicinity of main lobe with directive antennas. Third, a new technique is presented to realize a wideband hologram compact antenna test range (CATR) by linearly adjusting the feed location. The wideband formulas for linearly adjusting the feed have been discussed and verified. The performance of the wideband operation has been demonstrated by the measured results at W (95 GHz) and D (170 GHz) bands for the hologram aperture diameter of 350 mm. The dissertation also discusses characterization of quasi-optics, namely, MEMS-based highimpedance surface (HIS) and reflectarray elements. First, the reflection properties of the single unit cell structure of MEMS-based HIS is studied, tunability of the MEMS varactors and beam steering of a large structure at 80 GHz has been demonstrated with a simplified model. The structure allows steering of the beam within the range from -45o to +45°. A quasi-optical measurement setup has been built for the experimental characterization. Second, the design and optimization process of reconfigurable reflectarray element integrated with MEMS-based phase shifter at 120 GHz is studied. Also, the dielectric properties of SU-8 substrate have been characterized with on-wafer measurements. Several design parameters which could affect the modulation efficiency have been studied.This dissertation focuses on the development of characterization methods for antennas and quasi-optical components. The dissertation presents three new methods to deal with certain limitations occurred during the antenna measurement processes. First, a new technique using the Chebyshev polynomials has been proposed to process the antenna measurements obtained in non-anechoic sites to obtain equivalent free space radiation patterns. This new technique combines the principle of a FFT-based method with the special relationship between coefficients of the BesselChebyshev polynomials. Experimental results are presented to demonstrate the potential of this approach over conventional time gating techniques for a certain class of problems. Second, a new antenna pattern retrieval method is proposed. In this method, the antenna reflection coefficient is measured many times when a unique reflective load with known spatial reflection properties is placed near the antenna in each measurement. The antenna pattern is obtained from the measurements with an inversion algorithm. Simulations have been used to verify the theoretical basis and the method has been experimentally demonstrated at 30 GHz. The results show that the method could enable sufficient accuracy with low gain antennas or in the vicinity of main lobe with directive antennas. Third, a new technique is presented to realize a wideband hologram compact antenna test range (CATR) by linearly adjusting the feed location. The wideband formulas for linearly adjusting the feed have been discussed and verified. The performance of the wideband operation has been demonstrated by the measured results at W (95 GHz) and D (170 GHz) bands for the hologram aperture diameter of 350 mm. The dissertation also discusses characterization of quasi-optics, namely, MEMS-based highimpedance surface (HIS) and reflectarray elements. First, the reflection properties of the single unit cell structure of MEMS-based HIS is studied, tunability of the MEMS varactors and beam steering of a large structure at 80 GHz has been demonstrated with a simplified model. The structure allows steering of the beam within the range from -45o to +45°. A quasi-optical measurement setup has been built for the experimental characterization. Second, the design and optimization process of reconfigurable reflectarray element integrated with MEMS-based phase shifter at 120 GHz is studied. Also, the dielectric properties of SU-8 substrate have been characterized with on-wafer measurements. Several design parameters which could affect the modulation efficiency have been studied.