Inexpensive GPS mobile Antenna
Build a compact, circularly polarized GPS antenna for mobile use with common materials.
Description
For amateur radio operators utilizing APRS or requiring an external antenna for their GPS receiver, this resource details the construction of a compact, circularly polarized mobile antenna. The design is based on a classic turnstile configuration, employing two dipoles rotated 90° from each other and spaced a quarter-wavelength above a ground plane. A parallel-plate transmission line, fabricated from printed circuit board material, serves as both the connection method and mounting post for the dipoles, simplifying the feed network for circular polarization at 1.57542 GHz.
The article outlines the fabrication process, starting with a 4-inch diameter hobby tin or brass base plate and #14 solid copper wire elements. It specifies using RG-58/U or similar 50-ohm coax, with an 8-foot maximum length to minimize loss at the GPS frequency. The parallel-plate transmission line is constructed from two 2-inch lengths of single-sided FR-4 or G10 PCB material, 0.062-inch thick, with a specific 45° microwave turn cut on the active side. Final assembly involves an 8-ounce cream cheese container as a radome, and the article discusses the self-phased quadrature feed method to achieve circular polarization without a coaxial phasing line, resulting in an omnidirectional pattern suitable for GPS satellite reception.