Antenna element bandwidth and adaptive array performance

Abstract

It is well known that the radiation patterns of the individual elements, as well as the antenna geometry, affect the performance of an adaptive antenna array. In the open literature, these effects have been studied for single tone (CW) interfering signals. In the real world, the interfering signals incident on an antenna array are hardly single tones. Depending on the environment, the interfering signals can have the same bandwidth as the desired signals. Under these conditions, the response of the individual antenna elements over the system bandwidth would effect the adaptive antenna performance. In general, individual antenna elements are dispersive; i.e., the phase of the signal received by an antenna varies nonlinearly with frequency. This is especially true for narrowband antenna elements (thin dipoles, monopoles, patch antennas, etc.). When these antenna elements are used in an antenna array, the presence of the mutual coupling leads to dissimilar in situ element patterns. Thus, various channels of an adaptive array will be dispersive and dissimilar. This means that the adaptive array may have to use more degrees of freedom to null wideband interfering signals. The choice of individual antenna elements, therefore, can have significant effect on the performance of an adaptive antenna. In this paper, the same is demonstrated using an array of thin dipoles and another array of biconical antennas. It is shown that in the presence of wideband jammers the biconical antenna array performs significantly better than the dipole antenna array