An antenna may be designed for high directivity in one plane only or in both planes, depending on the application. The power gain of an antenna increases as the degree of directivity increases because the power is concentrated into a narrow beam and less power is required to cover the same distance. Since microwave antennas are predominantly unidirectional, the examples you will study in this chapter are all of the unidirectional type. Reciprocity You read in this chapter that an antenna is able to both transmit and receive electromagnetic energy. Antenna reciprocity is possible because antenna characteristics are essentially the same regardless of whether an antenna is transmitting or receiving electromagnetic energy.
Reciprocity allows most radar and communications systems to operate with only one antenna.
Duplexer operation will be. Because of the reciprocity of antennas, this chapter will discuss antennas from the viewpoint of the transmitting cycle. However, you should understand that the same principles apply on the receiving cycle. Radar Fundamentals Radio, television, radar, and the human eye have much in common because they all process the same type of electromagnetic energy. The major difference between the light processed by the human eye and the radio-frequency energy processed by radio and radar is frequency.