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Increasing customer expectations, combined with the expanding application of high-performance media delivery systems, requires a high performance level be achieved for automotive FM reception with the existing analog broadcast technology. Multipath distortion is often cited as a leading industry concern that can limit the quality of mobile FM reception. FM diversity has been identified as a potential methodology for improving the reception performance under multipath conditions. However, the delay time and strength of any signal reflections can vary considerably under differing terrain and geographic conditions. The corresponding amplitude and phase disturbances within the transmission channel are significantly different as a function of the propagation environment. Additionally, the specific implementation strategy and architecture of the diversity system can have a significant impact on the performance effectiveness of the system.

Whip antennas have been used for automotive AM/FM reception for many years. Although these systems typically offer very good reception performance, they suffer from other disadvantages including wind noise and aerodynamic drag, styling detraction, and the potential for mechanical damage. These limitations offer a significant incentive for developing concealed AM/FM antenna systems for the automobile. The concept of using a concealed antenna system for AM/FM reception is not new. However, previous concealed antenna designs have suffered from poor EMC performance and lack of sufficient gain for reception of distant stations under weak field strength conditions. Recent advances in the design and test methodology for concealed antenna systems have resulted in subjective performance that is equivalent to, and under certain circumstances exceeds, the performance level of a traditional whip antenna.

Increasing application of high-performance audio media and sound systems requires new levels of performance be achieved in automotive FM reception. Multipath distortion has been identified as a leading industry concern which often limits the quality of FM reception. Laboratory tests will be used to empirically quantify the effects resulting from a direct wave combining with a single reflected wave at the receiver. The reflected wave will be adjusted in amplitude, phase, and delay time to simulate conditions of mild, moderate, and severe multipath. The effects on the stereo signal will be characterized by the following parameters: 1. Total Harmonic distortion (% THD) 2. Signal-to-Noise Ratio (dB.) 3. Stereo Separation (dB.) Additionally, the effects of the modulating frequency and carrier deviation will be explored. Data will quantify potential improvements in THD and signal-to-noise ratio by reducing the stereo separation in the receiver.