Adaptive GNSS Antenna Matching for Low-Cost Applications

This paper presents a methodology for adapting the global navigation satellite systems (GNSS) antenna resonance frequency to different environments at a minimal cost. De-tuning effects of GNSS antennas due to the environment or manufacturing tolerances, especially for very compact narrow band antennas, significantly reduce the realized right-hand circular polarized (RHCP) gain of the antenna and hence the carrier-to-noise ratio of navigation signal. This has a detrimental effect on the acquisition, tracking and finally navigation performance of the system. This methodology contains an RF switch with different pre-defined matching components. A supervisory system uses knowledge of the received signal, i.e. the carrier-to-noise ratio and other signal indicators and switches between the matching options to maximize the realized RHCP gain. This increases the signal quality and finally improves the performance of the GNSS receiver. It is shown in simulation that the de-tuning of a single-band antenna due to a too small ground plane can be compensated with simple capacitive and inductive loading at the feed point. Furthermore, it is demonstrated that also the resonances of a dual-band antenna can be shifted independently with the same approach.