Title :
Reflectarray Design for 120-GHz Radar Application: Measurement Results
Author :
Tamminen, A. ; Makela, S. -M. ; Ala-Laurinaho, Juha ; Hakli, J. ; Koivisto, Paivi ; Rantakari, Pekka ; Saily, J. ; Luukanen, A. ; Raisanen, Antti V.
Author_Institution :
Dept. of Radio Sci. & Eng., Aalto Univ., Espoo, Finland
Abstract :
In this paper, we present design and experimental results on reflectarrays at 120 GHz. The offset-fed reflectarrays consist of conductor-backed coplanar patch antennas with phase-shifting stubs. Three 138-mm reflectarrays are lithographically fabricated and evaluated in a near-field measurement range. Their measured beam patterns are compared to the theoretical ones. The theoretical -3-dB beam width is 60-64 mm at 3-m distance from the reflectarray. Measured beam widths of the different reflectarrays deviate less than 10% from the theoretical values. The beam pointing is found to be close to theoretical, whereas the sidelobe level is up to 5 dB higher. The efficiency, alignment accuracy, and surface shape of the reflectarray are studied with near-field imaging of the reflectarray aperture field. The measured average efficiency is 0.11 whereas the predicted average efficiency is 0.54. The low efficiency is most likely due to over-etching of the structures of the reflectarray element, and could be improved in future fabrication processing rounds. Beam pattern measurement close to the main beam is well suited for evaluating the beam width and pointing accuracy, but it gives little information on the element performance. We propose near-field imaging of the reflectarray to evaluate both element efficiency and phase shift.
Keywords :
microstrip antenna arrays; millimetre wave antenna arrays; millimetre wave radar; phase shifters; reflectarray antennas; antenna array; beam pattern measurement; beam pointing; conductor-backed coplanar patch antenna; element efficiency evaluation; fabrication processing round; frequency 120 GHz; near-field imaging; near-field measurement range; offset-fed reflectarray; phase shift evaluation; phase-shifting stubs; radar application; reflectarray aperture field; reflectarray design; reflectarray element; sidelobe level; size 138 mm; size 60 mm to 64 mm; Antenna measurements; Feeds; Finite element analysis; Millimeter wave measurements; Phase shifters; Reflection; Reflector antennas; Antenna arrays; millimeter-wave measurements; near-field imaging; reflectarray;
Journal_Title :
Antennas and Propagation, IEEE Transactions on
DOI :
10.1109/TAP.2013.2273256