Electro-optical microwave signal processor for high frequency wideband frequency channelisation

An electro-optic microwave signal processor for activity monitoring in an Electronic Warfare receiver, offering wideband operation, parallel output in real time and 100% probability of intercept is presented, along with results from a prototype system. Requirements on Electronic Warfare receiver systems are demanding, because they have to detect and identify potential threats across a large frequency bandwidth and in the high pulse density expected of the battlefield environment. A technique of processing signals across a wide bandwidth is to use a channeliser in the receiver front-end, in order to produce a number of narrow band outputs that can be individually processed. In the presented signal processor, received microwave signals are upconverted onto an optical carrier using an electro-optic modulator and then spatially separated into a series of spots. The position and intensity of the spots is determined by the received signal(s) frequency and strength. Finally a photodiode array can be used for fast parallel data readout. Thus the signal processor output is fully channelised according to frequency. A prototype signal processor has been constructed, which can process microwave frequencies from 500MHz to 8GHz. A standard telecommunications electro-optic intensity modulator (Mach Zehnder interferometer in Lithium Niobate) with a 3dB bandwidth of similar to 2.5GHz provides frequency upconversion. Readout is achieved using either a near infrared camera or a 16 element linear photodiode array.