1. Field of the Invention
The present invention pertains to the field of antennas used for directive radio wave communications. More particularly it applies to microstrip antennas having a steerable array with parasitic elements and electronically controlled scanning.
2. Description of the Prior Art
It is known to utilize an antenna system having a linear microstrip array with a central receiving element and parasitic elements extended oppositely therefrom to adaptively steer an antenna pattern by phase shifters individual to the parasitic elements, such a system being particularly useful to steer a null toward an undesired microwave source. However, it is highly desirable to provide an antenna system having the compactness and simplicity of a microstrip array but steerable in azimuth and elevation in real time.
It is also known to steer such a linear microstrip array by circuits individual to the phase shifters where each such circuit has a oscillator providing a reference signal modulating the phase shifter, has a synchronous detector which receives the reference signal and the output of a receiver connected to the central elements, and has an integrator connected to the detector output and driving the phase shifter to minimize or maximize the receiver output. This manner of steering a microstrip array requires many circuit elements and is not easily adapted to other methods of steering to optimize the array pattern.
"Random search" and "guided random search" are iterative methods well-known for optimization when a number of variables must be adjusted. These methods have the advantage of rapid real-time convergence since all variables are adjusted simultaneously with the result that convergence may occur in less time than in other well-known optimization methods such as "steepest descent" where, although fewer complete iterations of all variables are required, the total time required is greater since at each iteration every variable must be adjusted individually and the effect measured.