Answers to RF Cafe Quiz #64

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Note: Many answers contain passages quoted in whole or in part from the text.

This
quiz is based on the information presented in
*Space-Time Adaptive Processing for Radar*, by J. R. Guerci.

Note: Some of these books are available as prizes in the monthly RF Cafe Giveaway

"Space-time adaptive processing (STAP) is an exciting technology for advanced radar systems that allows for significant performance enhancements over conventional approaches. Based on a time-tested course taught in industry, government and academia, this second edition reviews basic STAP concepts and methods, placing emphasis on implementation in real-world systems. It addresses the needs of radar engineers who are seeking to apply effective STAP techniques to their systems, and serves as an excellent reference for non-radar specialists with an interest in the signal processing applications of STAP. "

**1.** What was the original application of Space-Time Adaptive Processing (STAP)?

a) Moving target indication (MTI) radar

STAP was a term originally used for airborne multichannel moving target indication (MTI) radar.

(see page 53).

**2.** Why is moving target indication processing needed?

b) To enable detection of non-stationary objects within a background of stationary objects

The need for joint space and time processing in either airborne of space-borne MTI radar arises from the inherent two-dimensional, angle-Doppler nature of ground clutter when observed from a moving platform.

(see page 1)

**3.** What advantage does narrowband (c/B >> Nd) electromagnetic plane wave provide?

B = modulation bandwidth, N = number of elements, d = interelement spacing

d) Insures propagation across the array is manifested as a simple phase shift.

The effect of a unit-amplitude, narrowband EM plane wave impinging on an N-element ULA (uniform linear array) insures that propagation delay across the array is manifested as a simple phase shift.

(see page 13)

**4.** What are two key physical observables for MTI processing?

b) Doppler frequency and angle of arrival (AoA)

Besides AoA, another key physical observable for separating moving targets from noise is Doppler frequency.

(see page 30)

**5.** What are ramifications on adaptive processing due to variability in clutter terrain and other
interference nonstationaries?

c) They place practical limits on the size and quality of training data available

The number of adaptive degrees of freedom (DoFs) that can be utilized and supported in a given interference environment is highly dependent on variability in clutter terrain and other interference nonstationaries.

(see page 41)

**6.** What mathematical form does 'colored' noise take?

b) A nondiagonal covariance matrix

Space-time clutter is generally colored noise, that is, a nondiagonal covariance matrix.

(see page 53)

**
7.**
What is "the iceberg effect" (see chart at right)?

b) Increase in interference rank with increasing CNR due to realistic physical limitations

The iceberg effect describes the increase in interference rank (eigenvalues above noise floor) with increasing CNR when realistic eigenspectra are considered.

(see page 109)

**8.** What is another name for a structured-covariance method of STAP?

d) Model-based method

Structured-covariance methods, also referred to sometimes as model-based methods, refer to techniques that explicitly incorporate specific mathematical constraints or structures into the covariance estimation process.

(see page 153)

**9.** For which case is the max SINR (signal-to-interference-plus-noise-ratio) beamformer statistically
optimal?

a) Additive Gaussian interference

For the additive Gaussian interference case, the max SINR beamformer can be shown to be statistically optimal.

(see page 173)

**10.** What is a major advantage to radar clutter returns of having a prediction horizon on the
order of only seconds?

a) A significant degree of determination, and thus predictability

There is a significant degree of determination - and thus predictability - to radar clutter returns, particularly if the prediction horizon is only on the order of seconds.

(see page 253)