Pattern synthesis and design of a microstrip wire grid monopulse antenna

Abstract

The design of a monopulse microstrip wire grid antenna array is presented with simultaneously low side lobe levels in the sum pattern as well as both azimuth difference and elevation difference patterns. Monopulse antennas are a class of antennas used for direction finding in radar systems, and the control of side lobe levels is important to help with clutter rejection. The microstrip wire grid array is ideally suited to monopulse applications, and it has been shown in the literature that side lobes can be lowered by implementing an excitation taper across the aperture. Although it has been demonstrated in the literature that side lobes could be lowered for the sum pattern by applying a Taylor taper to the element excitation, it has not been shown that the antenna can be designed to produce an exact side lobe level. This work develops a synthesis method to design an excitation taper that would produce simultaneously low side lobes for the sum and both difference patterns. The resulting side lobe levels are a compromise between the patterns, since it is not possible to have arbitrarily low side lobe levels in all the antenna patterns without using complex feed structures and incorporating sub-arraying. This is true for monopulse antennas in general. The result of this work shows that it is quite difficult to achieve an exact side lobe requirement with a specific excitation taper, since mutual coupling and the current distribution at the feed affect the current distribution across the entire antenna in different ways depending on the antenna mode, or pattern generated.