Null Shifting with Fixed Delays
NAVAL COMMAND CONTROL AND OCEAN SURVEILLANCE CENTER RDT AND E DIV SAN DIEGO CA
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We demonstrate null shifting over a 1 GHz bandwidth using a fiber optic and integrated optic transversal filter. The null dept for our system is greater than 70 dB measured with a 10 kHz IF bandwidth. The null shifting is achieved by varying the tap weight values. Null shifting in the response of a transversal filter is directly related to null steering for a radar direction finder. The fixed delays consist of optical fibers cut at 10 centimeter increments. Integrated optical 2 x 2 couplers are used as the tap weights. The weighting is controlled by an applied voltage. The depth of the null is limited by the dynamic range of the sourcedetector combination. Ordinary fixed weight fiber optic transversal filters are subject to dynamic range and bandwidth limitations due to errors in cutting the fiber lengths. This problem can be remedied by using variable taps to shift the null frequency. The null depth and resolution is not detrimentally effected by using this approach.
- Active and Passive Radar Detection and Equipment