ABSTRACT
Active antennas in automotive systems increase the reception sensitivity and dynamic range of a receiving system. Low noise amplifiers are used in most receiving automotive systems: satellite digital audio radio service, global positioning system, Frequency modulated/amplitude modulated printed-on-glass antennas, digital audio broadcasting and other types of antennas. The diversity antenna system uses two or more spaced antennas with one receiver to improve reception quality. The chapter describes the signal-to-noise ratio that can be obtained with an active rather than passive antenna. Antenna noise temperature is defined as the temperature of a hypothetical resistor at the input of an ideal noise-free receiver that would generate the same output noise power per unit bandwidth as that at the antenna output at a specified frequency. If the antenna has very low radiation resistance, impedance matching of antenna and amplifier input is difficult. Active antenna gain can be measured with the standard gain transfer method by a reference antenna with a known gain value.
