Designers of mobile satellite communication antenna systems are faced with a number of conflicting system requirements. The link budget benefits from higher gain, but an omnidirectional pattern is best from a system coverage perspective. The antennas should be low profile and yet have good low elevation angle performance. They should also be small and yet have sufficiently wide bandwidth.
Exploring these trade-offs typically leads to the selection of patch antenna technology if maintaining a low profile is critical, or helical antennas if profile is less important but low elevation angle performance is vital. Furthermore, maintaining low cost is critical for commercial applications.
While a patch antenna is typically low profile, there are a number of problems with the patch antenna, namely the low elevation angle performance is not good, in the case where the antenna and transceiver are integrated onto a single PCB, it takes up a large amount of space on the top side of the transceiver, forcing the electronics to the bottom side, limiting miniaturization. Moreover, the patch antenna requires a substantial ground plane further miniaturization and there is a difficult bandwidth/volume trade-off.
While a helical antenna typically has good low elevation angle performance, there are a number of problems with the helical antennas. They have a relatively high profile, typically a significant fraction of a wavelength in height, the radiation pattern is typically impaired by the ground plane/electronics PCB, and they take up a large amount of space on the top side of the transceiver.
Another substantially omnidirectional antenna is the curled inverted-F antenna (CIFA). This is essentially an inverted-F antenna with a curled-end. With the curled end and optimized placement and orientation in the corner of an optimally sized ground plane, reasonably good circular polarization performance can be achieved. One example of such an antenna is sold by TE Connectivity under part no. 1513634-1. This GPS antenna is about 6 mm in height and 16 mm in diameter.
While this antenna is compact and lends itself well to integration along with other components on the same PCB, it has a number of limitations, including narrow bandwidth (only about 22 MHz for the 1513634-1), and intrinsic radiation pattern issues, such as a tilted beam with non-uniform RHCP (Right Hand Circular Polarization) coverage, which would mitigate against using this kind of antenna for some GEO applications.
Diversity antenna systems are known, for example, as described in U.S. Pat. No. 8,305,270 to mitigate multipath fading, particularly deep fades. Known diversity systems do not improve system performance in situations where fading is not a factor.