Study of Loaded Microstrip Antennas and Their Applications to Arrays.

摘要

An experimental study of reactively loaded rectangular microstrip antennas is presented in this report. The reactive loads used here were either a single pin, or a symmetrically located pair of pins, short circuiting points on the patch to corresponding points on the ground plane. A set of points forming a single curve for the case of one shorting pin or two symmetrically located curves for the case of two shorting pins was found. A single, or a pair of short circuits placed at any point on these curves results in an element having a fixed resonant frequency and a fixed radiation pattern independent of the point selected. The input impedance, however, varies over a very large range when a short circuit or pair of short circuits is moved along these curves. The major application of this work is the study of the feasibility of maintaining an impedance match for the elements of a microstrip antenna array with changing scan angle by moving the position of one or two short-circuiting pins. An experimental and theoretical study of the mutual impedance for microstrip array elements was conducted and used in a computer program simulating a finite array. Though the model used for mutual impedance was some what crude, the simulation program predicted a variation of active element impedance with scan angle. For a number of different scan angles, the position of shorting pins was adjusted to obtain a match for all of the array elements thus indicating that this dynamic matching technique may be feasible for scanned arrays.