S-Parameter Measurements For Multibeam Luneburg Lens Antenna

Summary form only given. Luneburg lenses are a very interesting solution when simultaneous reception from several different directions is desired. The lens concentrates the feed radiated field in a narrow beam in the direction of interest. The more feeds illuminating the lens, the more beams achieved. However, mutual coupling and blocking between feeds illuminating the lens impose limitations in the number of beams or the proximity between them. A previous study of the behavior of the mutual coupling of a Luneburg lens feeds has been carried out for spacing between feeds greater than 15 degrees (D. Franco-Vazquez, M. Vera-Isasa, E. de Lorenzo Rodríguez, PIERS Proceedings, 1862-1865, August 12-15, Stockholm, 2013).In this contribution, an S-parameter analysis based on measurements obtained for spacing between feeds lower than 15o within a frequency range from 8 to 11GHz is presented. The antenna under test is a 356mm diameter Luneburg lens illuminated at 193mm focal distance by two slightly flared vertical polarized WR90 feeds with aperture dimensions 26x13mm. The antenna under test is placed inside an anechoic chamber to perform the coupling measurements. The two waveguides are placed around the lens at the focal point, one in a fixed angular position (fixed waveguide) whereas the other (mobile waveguide) is initially placed as close to the fixed waveguide as possible and then it is moved away around the lens with a step of one degree. The fixed waveguide is connected to the port 1 of a four-port Rhode & Schwartz ZVA-67 network analyzer, and the mobile waveguide is connected to the port 2. The S21 parameter given by the network analyzer is recorded for further processing at every angular separation between feeds for both vertical and horizontal polarizations within the frequency range 8-11GHz.