OVERVIEW

Interferometers can be considered specific cases of array antennas. The linear array in which all antenna elements center lie in a straight line at equal spacings with beam forming done by phase shift networks is an example. In an interferometer, the elements can also lie in a straight line but are usually at different spacings to obtain time-of-arrival relationships that can be transposed into measurable phase differences for determination of angle-of-arrival information. The concept also extends to the circular array, where interferometer techniques can be applied to also cover 360 degrees of azimuth from an antenna mounted at one point.

In Chapter 2, Section 2.21, the simple interferometer antenna system was described as a DF measurement technique based upon the difference of the time of arrival of a signal detected by two identical collocated antennas in space separated by a finite base line. It was shown that the output of the antennas differed in phase from each other in proportion to the extra time it took a plane wave signal to travel a greater distance to the further antenna. Since a signal would be detected at the same time if it were equally displaced from both antennas, the phase difference would be zero, creating a phase difference null along the boresight for this condition. The measurement of the time difference or phase, whenever it is greater or less than zero, therefore, can give the incoming angle with respect to boresight.

A DF system consisting of two monopulses in space...