Reviews the development of these components which subsequently went into production. In order to appreciate the role of these components it may be appropriate to describe briefly the three basic principles which are applied to D/F receivers. These are: amplitude comparison; phase comparison (by interferometry); and phase/amplitude comparison using a two channel receiver and a single multimode spiral antenna. The features of interest in these receivers are the beam or mode forming networks and the down converters. A typical beam forming network for an amplitude comparison monopulse receiver is given, and contains four interconnected 180 degrees /3 dB hybrids. This network derives the sum and the two difference signals, i.e. elevation and azimuth, from the four symmetrically arranged antennae squinted off the axis. This provides a zero boresight system. This arrangement can be used equally well for phase comparison. In this case the four antennae face forward and lie on the same plane. The network performs a phase to amplitude conversion and the sum and difference signals are processed in the same manner as the amplitude comparison receiver.
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