Chapter 9: Moving Target Indicators (MTI)
J. Patrick Reilly
MTI systems comprise the most widely used class of radar processors for detecting moving targets in a background of clutter. Clutter is distinguished from receiver noise by its relatively narrow, low-frequency spectrum, which implies that these echoes are correlated from one sample to the next. Because of this property it is possible to reduce the effects of clutter with fiters that reject energy at clutter frequencies but pass the Doppler-shifted echoes from targets having higher velocities than the clutter. A processor that distinguishes moving targets from clutter by virtue of the differences in their spectra is called a moving target indicator or simply MTI. The simplest MTI processor, the single delay-line canceler, subtracts two successive echoes from the same location; reflections from stationary objects cancel, while those from moving targets produce fluctuating signals. When an MTI processor is cascaded or combined with a pulse Doppler processor, it is usually referred to as a moving target detector (MTD). Principles of MTD processing are discussed in Chap. 14.
MTI processors built around delay-line cancelers have been used since World War II. Early systems were primarily limited by system instabilities such as oscillator incoherence. Subsequent equipment refinements have in many cases shifted the main source of limitation from equipment instabilities to the characteristics of the clutter itself.
MTI canceler systems maximize signal-to-clutter ratios only for highly correlated interference. It should be understood that, to maximize the signal-to-noise ratio, the radar system must also contain a matched filter for...