The purpose of the radar antenna is to act as a transducer between free-space propagation and guided-wave (transmission-line) propagation.The function of the antenna during transmission is to concentrate the radiated energy into a shaped beam which points in the desired direction in space. On reception the antenna collects the energy contained in the echo signal and delivers in to the receiver.Thus the radar antenna is called upon to fulfill reciprocal but related roles.In the radar equation derived these two roles were expressed by the transmitting gain and the effective receiving aperture.The two parameters are proportional to one mitting gain and the effective receiving aperture implies a large transmitting gain another.An antenna with a large effective receiving aperture gain.
The large apertures required for long-range detection results in narrow beam widths, one of the prime characteristics of radar.Narrow beam widths are important if accurate angular measurements are to be made or if targets close to one another are to be resolved.The advantage of microwave frequencies for radar application is that with apertures of relatively small physical size, but large in terms of wavelengths, narrow beam widths can obtained conveniently
Radar antennas are characterized by directive beams which are scanned, usually rapidly.The parabolic reflector, well know in optics has been extensively employed in radar. The vast majority of radar antenna use the parabolic reflector, in one from or another. microwave lenses have also found some radar application,as have mechanically rotated array antennas.The electronically scanned phased array, is an antenna with unique properties that has been of particular interest for radar application
The radar antenna will be considered either as a transmitting or a receiving device,depending on which is more convenient for the particular discussion.Results obtained for one may be readily applied to the because of the reciprocity theorem of antenna theory.
Directive gain
- Power gain
- Effective aperture
- polarization
- Sidelobe radiation
- Aperture efficiency
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