18-40 GHz Spiral Antenna

The development of an 18-40 GHz spiral antenna is described. Its output, which is in line with its axis, is in double ridged waveguide WRD180C24. The antenna has an aperture diameter of 12mm which is increased to 16mm with the addition of an integral radome. Its overall length, including the radome, is 48mm. The antenna and radome together weigh only 14.5g. The antenna has a match of 2:1 and its gain is about 3dB higher than conventional spiral antennas. A unique solution to the problem of beam squint is presented. It is shown that with the introduction of a choke the maximum squint is reduced from 20 deg. to 3 deg. The large sample of radiation patterns presented exhibit low axial ratio and very symmetrical radiation. The small size of the antenna, coupled with its good amplitude performance, make it an ideal element in a phase and or amplitude comparison system.