Broadband multi-emitter signal analysis and direction finding using a dual-port interferometric photonic spectrum analyzer based on spatial-spectral materials

Abstract

A broadband signal analyzer that can determine the power spectra and direction of all spectrally non-overlapping emitters for a two antenna system is proposed and demonstrated. A spectrum analyzer (SA) based on spatial-spectral (S2) materials has previously been demonstrated that can monitor broadband signals (over several tens of gigahertz (GHz)) with sub-megahertz (MHz) resolution in real-time (sub-millisecond updates). Here, a dual-channel S2 SA is used to monitor the two outputs of a dual-drive dual-port optical Mach-Zehnder interferometer, where the RF inputs to the interferometer are driven by microwave signals with various time delayed components, emulating the outputs of a two-element antenna array receiving signals from emitters with various bandwidths, formats, and center frequencies. The sensitivity of the optical power spectra of the two output ports to the time delay of each resolvable frequency component of the signals enables the determination of energy and direction of each resolvable frequency component of multiple emitters. A simple post-processing technique is used to estimate the angle of arrival (AoA) and power spectrum of each emitter. The interferometric technique works on a variety of signals including short bursts of variable bandwidth frequency agile microwave signals. The system's direction finding (DF) and SA capabilities enable it to simultaneously monitor multiple types of emitters. With the current system architecture, tone bursts, spread-spectrum waveforms, and chirped waveforms over 5 GHz of bandwidth were demonstrated. Sub-picosecond resolution (sub-0.5 degree angular resolution on bore-site for signals with a 3.8 GHz carrier frequency) was demonstrated for signals with a 19 dB signal-to-noise ratio (SNR) at 1 MHz spectral resolution. The theoretical and measured resolutions are shown to be in good agreement.