Definitions

Active radar target enhancer
An electronic system that responds to a received radar pulse by transmitting a similar radar pulse.  Target detection is improved because the actively transmitted pulse is generally more powerful than would be the case with passive reflection.  The more common type of active RTE receives a radar pulse, amplifies it, and transmits the amplified pulse back toward the radar set.  In this case, the transmitted pulse is the same width and frequency as the incoming pulse.  A less common type is similar to an SART in that the transmitted pulse sweeps in frequency over the entire X-band frequency range, resulting in the blip displayed on the radar screen being displaced from the true target position by between 0.1 and 0.7 nautical miles.

Analytic RCS diagram
A multi-color display in which color represents the magnitude of radar cross section vs. azimuth and elevation. Usually used for RCS data calculated from analytic formulas, whereas the similar target pattern map (TPM) is usually used for measured RCS data.

Antenna gain
Ratio of the power transmitted along the peak of the beam to the power delivered to the antenna. A good approximation is G=20,000/(BW_H*BW_V) for horizontal beamwidth BW_H and vertical beamwidth BW_V in degrees.

ARPA
Automated Radar Plotting Assistant; software that tracks individual radar targets and determines risk of collision. ARPA computes such quantities as target course, speed, time of closest approach, and point of closest approach. ARPA requires several sweeps of the antenna, i.e. several successive detected blips, to establish a target track and usually requires detection on at least 50% of antenna sweeps to maintain track and establish risk of collision.

Aspect
Orientation of an object. In our situation, the orientation of a radar reflector relative to the radar.

Attenuation
Loss of signal power due to the propagation path not being a vacuum. Fog, precipitation, dust, etc may all cause attenuation. Loss in signal power may be due to absorption by the propagation medium or to scattering of energy away from the target and/or receiver.

Beamwidth
Radiation pattern width between half-power points.

Blind zone
Range intervals in which a target is not detected by radar because of destructive interference between the direct path and reflected path.

Capped (Luneburg) lens
A passive radar reflector made by putting a reflective cap on one side of a Luneburg lens.

Clutter
General term for pulse energy received by the radar set but which is reflected by objects other than the actual target. Clutter from precipitation, waves, and land are of primary concern to radar engineers.

Detection threshold
A pulse is detected if the power exceeds the threshold established by the user. In more detail, the detection threshold established the probability of false alarm. Once the threshold is set the probability of detection is a smooth function of received signal-to-noise ration. "Very good" detection is taken to be a probability of detection equal to 0.99, i.e. out of 100 pulses at the threshold power level, one can expect 99 to be detected and 1 to be missed. Pulses with power level lower than the detection threshold may still be detected through with lower probability.

Dihedral
Reflector formed by two flat plates at a right angle to each other.