What is the difference between a channelized receiver and a compressive receiver for ESM?

Channelized receivers and compressive (microscan) receivers are two architectures used in ESM systems to achieve wideband frequency coverage with high probability of intercept. They use fundamentally different approaches to determine the frequency of intercepted signals: (1) Channelized receiver: the input band is divided into many parallel channels using a bank of bandpass filters. Each channel covers a narrow slice of the spectrum (typically 10-100 MHz per channel). Each channel has its own detector (or digitizer) that reports whether a signal is present. To cover 2-18 GHz with 20 MHz channels: 800 channels needed. The frequency resolution equals the channel bandwidth. Advantages: 100% POI (all channels are monitored simultaneously), good sensitivity (narrow channel bandwidth means low noise per channel), and simultaneous signal handling (detects multiple signals on different frequencies at the same time). Disadvantages: complex and expensive (hundreds of filters and detectors), large size and weight, high power consumption, and the frequency resolution is limited by the channel bandwidth. (2) Compressive (microscan) receiver: uses a dispersive delay line (DDL) to convert frequency information into time information. The input signal is mixed with a rapidly swept LO (or passed through a chirp filter). Different input frequencies arrive at the detector at different times. By measuring the time of arrival at the detector: the input frequency is determined. Advantages: wide instantaneous bandwidth (2-18 GHz in a single sweep), fine frequency resolution (1-10 MHz, better than most channelized receivers), simpler hardware than a channelized receiver (one dispersive element instead of hundreds of filters). Disadvantages: limited dynamic range (the compressive receiver is essentially a correlator, and strong signals can mask weak ones), sweep time creates a dead time (signals present during the sweep transition are missed), and simultaneous signals at similar frequencies may not be resolved. (3) Modern trend: both architectures are being replaced by direct digital receivers (wideband ADC + FPGA channelization). The digital approach provides: the 100% POI of a channelized receiver, the fine frequency resolution of a compressive receiver, and programmable channel bandwidth and detection algorithms.