Abstract: In one embodiment, an antenna has four equally spaced monopole elements mounted in a symmetric array on the outer surface of a solid cylinder structure. The cylinder has a high dielectric constant, and extends from a conductive ground plane. The monopole elements can be switched by switching elements so that one or more is active, with the others acting as parasitic directors/reflectors being connected commonly to ground or left in an open circuit condition to be effectively transparent.

Abstract: A PSK and phase modulation transmission system has a modulator and a demodulator. The modulator has a carrier frequency generator (21) coupled to a voltage controlled phase shifter (22). The modulation of the signal in the shifter (22) is controlled by modulation voltage generator (23). A transmitter (24) receives the output from the shifter (22) and transmits the modulated signal. The demodulator (30) includes a receiver section (31) for receiving the signal transmitted by the transmitter (24). The receiver (31) is coupled to a modified phase locked loop comprising a phase detector (32), a low pass filter (33), a sample and a hold circuit (34) and a voltage controlled oscillator (35). A lock control circuit (36) receives either the output from the receiver (31) or the output from the filter (33) to produce a lock in pulse from changes in the received signal or changes in the demodulated signal at the filter (33) for controlling the sample and hold circuit (34).