FOR AMPLITUDE MONOPULSE SYSTEMS, conventional antennas provide only a directional mode. To offer an omnidirectional mode, such antennas will require a complicated amplitude and/or phase calibration network. At Aerospace Electronics Co., Leo G. Maloratsky has developed an L-band switched directional/omnidirectional antenna module. It comprises a four-monopole antenna, switched beamforming network (SBFN), matching network, and interface.
The switched beamforming network's switchedline 0/180-deg. phase shifter provides switching between the directional and omnidirectional modes. That network includes four 90-deg. hybrids, which are connected through four inverters. Over a 10-percent frequency range, the experimental antenna module exhibited directional gain beyond +1.0 dBi from a 90- to 100-deg. beamwidth. It exhibited return loss of less than -13.0 dB, side/ back-lobe levels below -10.0 dB, and an RMS bearing error below 2 deg. See "Switched Directional/ Omnidirectional Antenna Module for Amplitude Monopulse Systems," IEEE Antennas And Propagation Magazine, October 2009, p. 90.