An experimental investigation of a spherical reflector antenna for operation in rain at millimeter wavelengths

This thesis is an extensive investigation of an innovative spherical reflector antenna design for operation at millimetre wavelengths in rain. Radiation pattern measurements were performed at three elevation angles (10°, 30°, 50°) and three frequencies (27.5 GHz, 31.5 GHz, 35 GHz). Wet-antenna attenuation measurements were also performed at three reflector angles (20°, 30°, 40°), and at the three frequencies mentioned above. The antenna investigated consists of a 30 cm diameter shallow spherical reflector with a relatively large ratio of focal length to diameter. The reflector is illuminated by a pyramidal feed horn which is fixed in a downward facing position, while the reflector swivels in the vertical plane to accommodate the direction of incident radiation. The antenna's performance was compared to that of a conventional parabolic reflector antenna under both dry and wet conditions with favourable results. Beamwidth values varied approximately between 1° and 3° and sidelobe levels varied approximately between -12 dB and -20 dB depending on the frequency and elevation angle. Under wet conditions the antenna performed quite well with a maximum observed attenuation level of 1.6 dB at the worst reflector angle used; while conventional reflector antennas experience attenuation levels of up to 10 dB. Cross-polarization discrimination of the dry antenna was also found to be approximately 34 dB.