Design, construction and analysis of a 14-bit direct digital antenna utilizing optical sampling and optimum SNS encoding
Ringer, William P
Pace, Phillip E.
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Direct digital direction finding (DF) antennas will allow an incoming signal to be digitally encoded at the antenna with high dynamic range (14 bits approx. equal 86 dB) without the use of down conversion that is typically necessary. As a shipboard DF device, it also allows for the encoding of wide band, high power signals (e.g., +/- 43 volts) that can often appear on shipboard antennas due to the presence of in band transmitters that are located close by. This design utilizes three pulsed laser driven Mach-Zehnder optical interferometers to sample the RF signal. Each channel requires only 6 bit accuracy (64 comparators) to produce an Optimum Symmetrical Number System (OSNS) residue representation of the input signal. These residues are then sent to a locally programmed Field Programmable Gate Array (FPGA) for decoding into a 14 bit digital representation of the input RF voltage. Modern day FPGA devices are rapidly becoming the state of the art in programmable logic. The inclusion of on chip flip flops allows for a fast and efficient pipelined approach to OSNS decoding. This thesis documents the first 14 bit digital antenna which utilizes an FPGA algorithm as a method of OSNS decoding. This design uses FPGA processors for both OSNS decoding and Parity processing
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