Switched Directional/Omnidirectional Antenna Module for Amplitude Monopulse Systems

An L-band switched directional/omnidirectional antenna module, consisting of a four-monopole antenna, a switched beamforming network (SBFN), a matching network, and an interface, is described. The antenna includes four folded monopoles, parasitic elements, a special base plate, a common capacitive top hat, and a radome. The special switched-line 0°/180° phase shifter of the switched beamforming network provides switching between the directional and the omnidirectional modes. The beamforming network (BFN) includes four 90° hybrids, connected with each other through four invertors. A practical application of this antenna module for aircraft amplitude monopulse systems is considered in this article. Over a frequency range of 10%, the experimental antenna module exhibited directional gain greater than +10 dBi, from 90° to 100° beamwidth, a return loss less than -13.0 dB, side/back lobe levels than -10.0 dB, and an rms bearing error of less than 2°.