Engineering Tutorials

"That part of a transmitting or receiving system which is designed to radiate or to receive electromagnetic waves". An antenna can also be viewed as a transitional structure (transducer) between free-space and a transmission line (such as a coaxial line). An important property of an antenna is the ability to focus and free shape the radiated power in space e.g.: it enhances the power in some wanted directions and suppresses the power in other directions .

Antennas focus the radio signal in a specific direction and in a narrow beam. The increase in the signal power (compared to an omni directional antenna) when it is focused in the desired direction is called gain.

Antennas are tuned to operate on a specific group of frequencies. Other specific attributes such as beam-width and gain are also fixed by the manufacturer. Antennas should be selected and placed according to the site and the application .

In general, the larger the antenna, the higher the gain and the larger the mast required. It is best to use the smallest antenna that will provide sufficient protection from interference and enough signal at the far end of the link to provide good reception even with fading.

Other considerations include antenna beam-width, front-to-side ratios, front-to-back ratios, and cross-polarization rejection. Where interference from other licensees on the same channel or adjacent channels is an issue, narrow beam-widths, high front-to-back and front-to-side ratios, and high cross-polarization rejection are likely to be required. Even when other licensees are not an issue, if using a network deployment using the “cell” approach, all these considerations is still important to reduce interference between own adjacent installations .