Antenna with cardioid directional pattern for COSPAS-SARSAT personal emergency radio beacon

A compact dipole-loop antenna with a cardioid directional pattern which is made for implementing into the second generation radio beacons of search and rescue COSPAS-SARSAT system has been presented. The antenna consists of superposed dipole and loop ra-diators. The loop radiator is made as a half-wave loop, what differs the antenna from the classic Huygens element realization. The antenna cardioid directional pattern forming conditions have been noted and the technical parameters of realization of these conditions have been determined.

A step algorithm of the antenna design has been presented. This algoritmn includes calculations of an asymmetric dipole, a half-wave loop with shortening capacitors, microstrip power divider, which feeds the loop and dipole, a balun, calculations of an assembled antenna and overall matching circuit and also a way of an antenna sample adjustment using the directional pattern shape.

Using the calculation and simulation results a compact (180×40 mm with 80×40 mm balance) antenna with a cardioid directional pattern, applicable in COSPAS-SARSAT system second generation radio beacons. Voltage standing wave ratio which is equal to 1,1 and gain in the directional pattern maximum which is equal to 2,5 dB have been experimentally obtained on the operating frequency 406 MHz. A transmitter PCB influence on the antenna characteristics have been viewed. By changing the balance shape, the antenna has been installed into the radio beacon with dimensions 200×75×45 mm.