Single-Element GPS Antenna with Adaptive Anti-Jamming Capability

The development of a "smart," anti-jam, single-element GPS antenna is proposed. The approach uses an electronically reconfigurable antenna (ERA) whose gain pattern has an azimuthal null which can be varied by adjusting control loads on the antenna. The loads are adjusted and controlled by an adaptive feedback network which uses receiver output to change the control elements and, thus, alter the antenna properties in an optimal manner (smart antenna). This will increase the signal to jammer ratio (SJR) at the antenna input. The antenna element will be a surface conformable microstrip spiral that is four or five inches in diameter and has variable control loads on each of the spiral arms. An analysis of such an antenna is shown for the L1 GPS frequency. It demonstrates that a narrow null in the antenna pattern can be steered in any azimuthal direction by varying the load impedances. The null is more than 40 dBi deep and is only a few degrees wide in a pattern that is otherwise isotropic with a gain of a few dBi. The feedback control network would maintain the jammer in this deep null.