Reading Guide: antenna is a kind of converter, which converts the guided wave transmitted on the transmission line into the electromagnetic wave transmitted in unbounded preamble (usually free space), perhaps the opposite.

A component used to transmit or receive electromagnetic waves in radio equipment. Engineering systems such as radio communication, radio, television, radar, navigation, electronic countermeasures, remote sensing, radio geography and so on, all those that use electromagnetic waves to transmit information rely on antennas. In addition, in terms of transmitting energy with electromagnetic waves, non signal energy radiation also needs an antenna. Ordinary antennas are reversible, that is, the same pair of antennas can be used as both transmitting and receiving antennas. The basic characteristic parameters of the same antenna as transmitting or receiving are the same, that is the mutual theorem of antennas.

 

In antenna measurement, the working state of the measured antenna can be transmitted or accepted. This can be selected sensitively according to the measurement content, measurement equipment, site conditions and other factors. It can be seen from the antenna interaction principle that the results of measuring antenna parameters under the two working states should be the same. However, in practical measurement, the interaction principle must be used under certain conditions.

Condition 1: the antenna must be linear and passive. For example, the satellite TV receiving antenna, whose feed is integrated with the LNB, cannot be used for transmission.

Condition 2: the impedance matching of the transceiver system should be prominent. Although there are multiple reflections between the antenna to be tested and the source antenna, the impact is not serious due to the attenuation of free space transmission. Impedance matching between source antenna, feeder, signal source, antenna to be tested, feeder and receiver is an important condition to meet the transaction principle.

Condition 3: when exchanging antennas, passive equipment of transceiver branch, such as power amplifier, low noise amplifier, mixer, etc.