Active Remote Sensor: Transmits radiation of specific ...



Active Remote Sensor: Transmits radiation of specific frequency (or frequency interval) and receives it via reflection or backscattering from a point target or distribution of targets (e.g., raindrops)

1. Introduction to radar

Good overview: man/dod-101/navy/docs/swos/cmd/fun12/12-1/sld006.htm

1. Background

Definitions: RADAR -- Radio Detection and Ranging

Range of wavelengths: 1 mm < λ < 10 m

Specific radar bands: refer to handout sheet

Doppler (coherent) radar – ability to measure change in phase of transmitted signal

Incoherent radar – phase change not measured, only magnitude of backscattered signal is measured

Radar strengths – ability to detect clouds, precipitation, and refractive index variations

Radar limiations – crude spatial resolution, spectral limitations, side lobe contamination, ambiguous signals

2. Radar History (Rinehart, pp. 1-4)

Radar

Meteorological radar

Doppler radar

Polarimetric radars

3. Radar hardware overview

1. Radar types

Pulsed – radiation emitted in short pulses (~1 μs) at some pulse repetition frequency (PRF)

Continuous wave (CW) – radiation emitted continuously

Bistatic – two antennas, one transmits and one receives

Monostratic – one antenna (transmits and receives), more common

2. Radar components

Transmitter

Source of EM radiation; generates signal at specific radio frequency (RF)

Transmitter types

Magnetron – an oscillator tube with resonant cavities (Fig. 6.2, Skolnik)

Developed in 1939

Small, relatively cheap

Can transmit signals with peak energy of ~500 kW

coaxial magnetron – improved power, frequency stability, efficiency and life (Fig. 6.3, Skolnik)

Fig. 2.2 in Rinehart

Example: HSV WSR-74C radar (coaxial magnetron)

Klystron – power amplifier fed by a RF oscillator (true amplifier)

Also contain cavities (Fig. 6.9, Skolnik)

Larger and more power, peak transmit power up to 2 MW

Good waveform, purer (very stable) transmit frequency

Also termed MOPA – Master Oscillator Power Amplifier

Example: WSR-88D radar

Solid state transmitter

Much lower power ( ................
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