14 March 2013 – Phased Antenna Arrays

Don, G4LOO, spoke of Phased Array Antennas and we were surprised to find there were so many types. Some for over the horizon radar, some for enhanced reception, some for shortwave broadcast, but the type of most interest to us was the four square vertical.

4SQ

Don described how he built a 40M system based on fibreglass poles held by short aluminium supports. The poles hold a quarter wave wire, helically wound. Each vertical has 32 quarter wave radials and at the point where the radials would have crossed at the centre of the configuration, they were instead, connected to a bus wire. Each of the verticals are connected by coax so that the signals can be switched to be either in phase or out of phase to either enhance the signal or suppress it.

HB sw

Of the four types of switching systems described, Don built the Collins Hybrid Phasing System.

Plot az 4sq

The overall antenna is expected to give a front to back ratio of well over 25 – 30dB depending on the incoming signal angle. The noise level on the antenna is also much lower than that of a single vertical and the beam switching can be done in a second!