How does a digital instantaneous frequency measurement receiver work?

A digital instantaneous frequency measurement (DIFM) receiver works by digitizing the incoming microwave signal and computing the instantaneous frequency using digital signal processing, providing rapid and accurate frequency measurement of each intercepted pulse across a wide bandwidth. The DIFM receiver architecture: a wideband antenna receives the signal. The signal is amplified by a wideband LNA and filtered to the band of interest. The signal is digitized by a high-speed ADC (sampling rate: 2-20+ GSPS for Nyquist coverage of the threat band). The instantaneous frequency is computed in an FPGA or DSP using one of several digital algorithms. Frequency measurement algorithms: digital autocorrelation (correlate the digitized signal with a delayed copy of itself; the phase of the correlation at a specific delay tau gives the frequency: f = delta_phi / (2 × pi × tau); this is the digital equivalent of the analog IFM receiver's discriminator), FFT-based (compute a short FFT (e.g., 64-256 points) on the digitized signal; the peak of the FFT gives the frequency; the FFT length determines the frequency resolution and measurement time), and Hilbert transform (compute the analytic signal using a Hilbert transform; the instantaneous frequency is the time derivative of the unwrapped phase). The DIFM offers advantages over the analog IFM: ability to handle simultaneous signals (an analog IFM produces erroneous readings when two signals are present simultaneously; a DIFM can resolve multiple simultaneous signals using FFT processing), higher accuracy (digital processing provides arbitrarily fine frequency resolution by adjusting the FFT length), and programmability (the algorithm can be updated or changed without hardware modification).