active antenna
Antennas are passive RF components that convert electromagnetic waves into RF voltage. If they are combined with integrated antenna amplifiers, they are referred to as active antennas.
The combination antenna with integrated antenna amplifier should not be confused with an antenna with downstream antenna amplifier. The difference lies in the antenna cable, which in the case of the downstream antenna amplifier is located between the two RF components and attenuates the RF signal before it reaches the input of the antenna amplifier. In addition, the antenna cable can pick up interference and electromagnetic noise fields.
To avoid losses through antenna cables, the antenna base of active antennas is directly connected to the input of the antenna amplifier. The input impedance of the antenna amplifier corresponds to the footpoint or antenna impedance. The integrated antenna amplifier amplifies the RF signals without first being affected by noise or other interfering signals. As a result, the signal-to-noise ratio( SNR) is much better than for antennas where the antenna amplifier is connected via a longer antenna cable. The bandwidth of the active antenna - antenna plus amplifier - corresponds to the frequency range for which the active concept is designed. So it can be relatively broadband.
Active antennas are characterized by a high antenna gain, they can be designed more broadband and thus cover several frequency bands. They are not only suitable for stationary operation, but are also used as car antennas. The so-called "shark fins" combine several antenna systems in a compact housing, including for FM, digital radio( DAB),high-definition television( HDTV), satellite radio( SR), traffic radio, digital traffic radio ( TMC), mobile telephony with GSM and UMTS, WiMAX and for the GPS system.