In an active antenna, an active device such as an amplifier or an oscillator is integrated with the passive antenna. The implementation of an amplifier in a passive antenna increases gain, and improves noise performance. Active microstrip antennas are very widely used because they are small, inexpensive, compact, efficient, and reliable. An overall system gain of 40dB is very practical in a two-stage configuration, while the noise factor is on the order of 3dB. Circularly polarized antennas are required for use with GPS, the single-fed design being less expensive and therefore preferred over dual-fed. The common two-stage amplifier incorporates a low-noise amplifier as the first stage and a high-gain amplifier as the second stage, for maximum gain and minimum noise factor. In this presentation, the design, fabrication and measurements of the active antenna will be discussed.
 

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