Global Positioning System (GPS) receivers are finding their way into many new mobile communications devices and in virtually every new automobile, thus heightening the need for smaller and more flexible antennas. To satisfy growing demands for GPS receivers, researchers from various Taiwanese institutions developed a miniature, low-cost, folded-patch GPS antenna for vehicular applications. It operates at the GPS center frequency of 1575 MHz with right-hand circular polarization (RHCP) in two orthogonal linear resonant modes.
RHCP enables a flexible orientation angle between the GPS receiver on the car and the satellite-based transmitter, reducing multipath reflections. The antenna, designed to be simple and inexpensive, was printed on two layers of economical FR-4 printed-circuit-board (PCB) material to lower cost. To obtain RHCP, the antenna is fabricated with four different lengths of meander strips connected to the four edges of a square circuit patch. The four meander lines are folded and the patch is excited by a single coaxial probe.
To better understand the folded antenna’s behavior under different conditions, it was designed with different ground planes to ensure effective operation when mounted on the metal roof of an automobile. The antenna was simulated via High Frequency Structure Simulator (HFSS) electromagnetic (EM) simulation software from Ansoft Corp. Return-loss measurements of the fabricated antennas were made on a commercial vector network analyzer from Agilent/Keysight Technologies.
Simulations were performed to analyze the effects of different ground-plane radii. They indicated that the location of the antenna on a vehicle roof has only a slight effect on performance, and does not impact the circular polarization performance. Close agreement was obtained between the simulated and measured results. Measurements revealed an approximate impedance bandwidth of about 2.1% for 10-dB return loss, from 1560 to 1593 MHz.
See: “Miniature Folded Patch GPS Antenna for Vehicle Communication Devices,” IEEE Transactions on Antennas and Propagation, May 2015, p. 1891.