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Radar 101 ● Assembled by: Justin Fiore ● Resources Mahafza, Bassem. Introduction to Radar Analysis. CRC Press, Boston, 1998. ● Guerci, J. R. Space-Time Adaptive Processing for Radar. Artech House, Boston, 2003. ● ● ISBN: 3 1735 039 622 869 ISBN: 3 1375 046 827 063 Web Resource for Pitt Wikipedia Articles: ● ● Beamforming Adaptive Beamformer
Common Terms ● ● PRI: Pulse Repetition Interval – The interval between transmission pulses. PRF: Pulse Repetition Frequency (fr) – The frequency of transmission pulses ● ● fr=(1/PRI) Unambiguous Range: Ru – The range corresponding to the two-way time delay (to and from the target). ● Ru = c/(2 fr)
Common Terms - Continued ● ● Range Resolution: ∆R – a radar metric that describes its ability to detect targets in close proximity to each other as distinct objects. Doppler Frequency – Radars use this to extract target radial velocity as well as distinguish between moving and stationary targets or clutter. For a moving target, there will be a shift in the center frequency of the incident waveform. Depending on the direction of movement, the frequency shift will be positive or negative.
Common Terms - Continued ● ● CW: Continuous Wave radar – Radars that continuously emit energy and use separate transmit and receive antennas. PR: Pulsed Radar – Radars that transmit pulses of energy and receive when not transmitting. They use the same antenna for transmitting and receiving. ● SCR: Signal to Clutter Ratio ● SNR: Signal to Noise Ratio ● SINR: Signal to Interference Plus Noise Ratio
Common Terms - Continued ● Clutter – any object that may generate unwanted radar returns that may interfere with normal radar operations. Surface Clutter – includes trees, ground terrain, man-made structures, and sea surface (also known as sea clutter). Airborne or Volume Clutter – includes chaff (radar decoys), rain, birds, insects, etc. Surface Clutter tends to vary much more than Volume clutter Often the clutter signal is much higher than the receiver's noise level.
Common Terms - Continued ● ● MTI: Moving Target Indicator STAP: Space-Time Adaptive Processing – Radar processing that involves space (typically an array of antennas), time, and adaptively tunes the processing. ● ULA: Uniform Linear Array ● Ao. A: Angle of Arrival ● Hadamard product: C = A○B – element-wise matrix multiplication. If A and B are Mx. N matrices, C will be an Mx. N also and Cij = Aij * Bij
Common Terms – Continued ● Beamforming - a signal processing technique used with arrays of transmitters or receivers that controls the directionality of, or sensitivity to, a radiation pattern. When receiving a signal, beamforming can increase the gain in the direction of wanted signals and decrease the gain in the direction of interference and noise. When transmitting a signal, beamforming can increase the gain in the direction the signal is to be sent. This is done by creating beams and nulls in the radiation pattern. Beamforming can also be thought of as spatial filtering.
Common Terms – Continued ● Adaptive Beamformer - a signal processing system often used with an array of radar antennae (or phased array) in order to transmit or receive signals in different directions without having to mechanically steer the array. The main distinction between an adaptive beamformer and a conventional beamforming system is the ability of the former to adjust its performance to suit differences in its environment. A particularly important feature, in military applications, is the potential for an adaptive beamformer to reduce sensitivity to certain directions of arrival so as to counteract jamming by hostile transmissions.