A four-element reflecto-nulling antenna array

In this paper, a novel approach is developed for achieving a reflecto-nulling antenna array which can make the null of re-transmitted radiation pattern at the reflection angle of the incident wave without using digital signal processing techniques. The array is designed by properly utilizing 90deg hybrids. For a 90deg hybrid, if the input port and isolated port are connected to the receiving antenna and transmitting antenna, it can be shown as the direct port and coupled port are terminated with two out-of-phase reflection coefficients Gamma and -Gamma, the re-transmitted radiation pattern will have a null at the specular direction -thetas_i when the incident angle is thetas_i. The formulas and measurement results of a four-element reflecto-nulling antenna array are presented with the measurement arrangement.