HF frequency hopped signal direction finding using an antenna array

Passively detecting and localizing a frequency hopped signal presents two challenging problems. First, the signal must be detected by identifying individual frequency hopped chips associated with the signal of interest. Second, the array responses corresponding to individual chips must be combined in some manner to produce a direction of arrival estimate. This paper addresses the second problem. It describes a direction finding approach for frequency hopped signals that utilizes an antenna array, a switching network, and two wideband receivers. We present a maximum likelihood based approach to direction finding using array element response pairs collected during individual chip periods. Using a synthesized frequency hopped signal created from HF ionospheric sounder measurements, array responses are generated, and the direction of arrival estimated using the maximum likelihood based approach. The results are presented.