Progress towards a wideband RF imager

RF imaging is the mapping of signal intensity to the available azimuth and elevation angles of arrival. Although the result is analogous to optical images, which are formed using optical lenses, RF imagers typically use processor-intensive synthesis imaging techniques to form the image from signals collected by an antenna array. As the antenna array element count and the bandwidth of the receivers grow, however, the required processing power rapidly increases. In the experiment presented in this paper, we choose an electro-optic process to form the RF images. We upconvert the array of antenna signals onto an spatial optical fiber array, which allows us to use a lens as a Fourier optical beamformer. As we show with initial results, this forms frequency-scaled narrowband images of the RF object onto an image plane where they may be detected by an optical camera. To collect wideband images, we must compensate for the narrowband frequency scaling, so we incorporate a spectral hole burning (SHB) crystal as a time integrating image channelizer. The SHB crystal integrates narrowband images within 1 MHz wide spectral bins across a spectral bandwidth up to 30 GHz. These narrowband images are sequentially read from the crystal and scaled by an external zoom lens such that, when integrated on an optical camera, they form a wideband image. We present experimental progress towards forming a one dimensional image across a frequency band of 2-4 GHz.