A 3-channel 14-bit optimum SNS wideband digital antenna: analysis of the electro-optic sampling front end

Abstract

Space considerations onboard naval surface ships frequently preclude adequate separation between high frequency (HF) transmit antennas and HF receive only antennas. As a result, high power shipboard emanations (for example Link- 11), interfere with low power signals of interest operating within the same frequency band. Symmetrical Number System (SNS) digital antennas provide high resolution direct digitization of wideband signals with excellent in band signal rejection characteristics, which makes them ideal for operating within high RF environments. This thesis describes the design, construction, testing and analysis of the optical electronics at the front end of a prototype optimum SNS digital antenna with a desired accuracy of 14 bits and a bandwidth of 2.5 MHz. The digital antenna utilizes pulsed laser sampling in conjunction with a parallel configuration of Mach-Zehnder interferometers which provide superior bandwidth and isolation performance over electronic sampling mechanisms. The interferometer folded output signal is in accordance with the optimum Symmetrical Number System (SNS) which yields the maximum amount of information from a folding waveform. The theory and experimental performance of the optical subsystem and the analog electronics subsystem is presented, and the total system performance is evaluated. A summary of results and a conclusion with recommendations for improvements to follow-on systems is also discussed