IFF antenna sharing the reflector with the C-band radar

The design of a IFF (Identification Friend or Foe) interrogator antenna (hereafter referred to IFF antenna) sharing the shaped reflector with the C-band radar is described. To ensure that each feed operates properly in the presence of the other, dipoles elements were tried as IFF feed, IFF feed elements beside and under the radar feed horn were also tried. In the end, two dipoles were used as IFF feed and were located under the radar feed horn, yielding approximately a 9° azimuth beamwidth and 1.7 dB per degree horizon cutoff. The sidelobe level of the sum beam is about -40dB, the difference beam is below -25dB.