Active Antennas
An active antenna is one that contains some electronic circuitry that can amplify a received signal at the antenna and thus avoid interference that may enter the system at the transmission line. Figure 27 shows this concept. The antenna “element” is connected to the input of an amplifier. The output terminals of the amplifier are the antenna terminals for this active antenna. The antenna element and the amplifier are included in the “active antenna,” shown as a dashed box in the figure.
Figure 27. A simple active antenna
Another purpose of an active antenna is to transform an unusual antenna terminal impedance to a constant value that matches the characteristic impedance of the transmission line. This function is useful for some antenna designs in which a specific pattern feature is desired, but cannot be achieved without causing the antenna to have an unusual terminal impedance. An active antenna is nonreciprocal and cannot be used for transmitting.
Comments
Post a Comment