ABSTRACT

The monopulse antenna, which is a key technique for angle estimation [170], is widely used in rapid direction-finding systems, radar systems, and communication systems. It is usually developed from antenna arrays with even and odd excitations to generate a pair of sum and difference beams. These sum and difference radiation patterns can be obtained through a pair of interleaved antenna arrays with different beam squints [171]. The sum and difference patterns can be also generated by antenna arrays that operate in either of even and odd modes of excitation with separate hybrid ports for each mode [172]. The poor performance of the gain and the angular sensitivity are the main drawbacks of the first overlapped beam technique. That is because the excitations of the equivalent sum and difference antenna arrays are far away from the ideal independent amplitude tapers. With proper excitations, two closely spaced antenna arrays were interleaved to obtain the monopulse in dual plane [173]. Cassegrain parabolic antennas or lens antennas are also commonly applied in monopulse antennas, but they are usually heavy and complicated. Some printed arrays have been utilized to realize monopulse antennas described in [174, 175]. However, the microstrip feedline may cause a large radiation loss from feeding paths, especially in the millimeter-wave frequency band.