Pulse Doppler SpectrumBy

Tariq Kanher

Pulse Doppler Spectrum

Pulse Doppler Clutter

Ground Clutter in Stationary Radar

Ground Clutter in Moving Radar

Sidelobe Clutter

Main Beam Clutter

Single Target Tracking

Multiple Target Tracking

Agenda

Pulse Doppler Spectrum

Pulse Doppler Spectrum

Pulse Doppler Spectrum

Pulse Doppler Spectrum

previous figure show the unfolded spectrum in caseof horizental motion of radar, with a velocity VR .

The clutter free region in define as that portion of thespectrum in which no ground clutter can exist.

The side lobe clutter region, 4VR /λ in width, containsground clutter power from the side lobes of theantenna, although the clutter power may be belowthe noise level in part of the region.

Pulse Doppler Spectrum

Altitude line clutter, which is due to ground clutter atnear normal incidence directly below the radarplatform, is at zero Doppler if there is no verticalcomponent of platform velocity.

A discrete target return in the main beam is shown at

fT = f0 + 2VR /λ cos (Ψo) + 2VT /λ cos (ΨT) ,where thetarget velocity is VT with an angle between the targetvelocity vector and radar target line of sight.

Pulse Doppler Spectrum

The main beam region , located at f0 + 2VR /λ cos(Ψo)contains the strong return from the main beam ofantenna striking the ground at scan angle of Ψomeasured from the velocity vector.

Rain and chaff clutter may also be large when themain beam illuminates a rain or chaff cloud. Motiondue to winds may displace and/or spread the return infrequency.

Pulse Doppler Spectrum

Clutter returns from various scatters have a stronginfluence on the design of a pulse Doppler radar aswell as an effect on the probability of detection ofpoint targets.

PULSE DOPPLER CLUTTER

When the radar is fixed with respect to the ground, both main-beam and side lobe clutter returns occur at zero Doppler offset, the transmit frequency.

The side lobe clutter is usually small compared with main beam clutter.

The clutter can be calculated as in a pulse radar, then

folded in range as a function of the PRF.

GROUND CLUTTER IN A STATIONARY RADAR

When the radar is moving with a velocity VR the clutter is spread over the frequency domain as illustrated in figure for special case of horizontal motion.

The fold over in range and Doppler is illustrated in next Fig for a medium-PRF radar where the clutter is

ambiguous in both range and Doppler.

Ground Clutter in a Moving Radar

The radar platform is moving to the right at 1000km with a drive angle of 10 degree.

The narrow annuli define the ground area that contributes to clutter in the selected range gate.

The five narrow hyperbolic bands define the area that contributes to clutter.

Ground Clutter in a Moving Radar

The entire clutter spectrum can be calculated for each range gate by Equation next slide, if the antenna pattern is known in the lower hemisphere.

In preliminary system design, the exact gain function may not be known, so that one useful approximation is that the side lobe radiation is isotropic with a constant gain of GSL .

Side lobe Clutter

The main-beam clutter-to-noise power can be approximated from equation

The summation limits are the lower and upper edges of the smaller of the transmit and receive beams.

Main-Beam Clutter

Main-Beam Clutter

Tracking can be identical to a congenital pulse radar using mono pulses, sequential lobbing or conical scan.

Mono pulse is more difficult to mechanize because of the problem of phase and amplitude matching of the multiple receiver channels.

Single-Target Tracking

Multiple target tracking can be accomplished in several ways.

One, track while scan , is to use normal search mode with FM or multiple PRF ranging and store the range, angle and Doppler of the reported detection in the computer.

Multiple-Target Tracking

A second method of multiple-target tracking, pause-while-scan, particularly applicable to electronic scan antennas, is to scan in a normal search pattern pause on each search detection, and enter a single-target track mode for a brief period.

PULSE DOPPLER RADAR

William H. Long

David H. Mooney

William A. Skillman

Westinghouse Electric Corporation

Reference