Four Main Effects on GPS Antenna Performance

Ceramic Wafer: ceramic powders and sintering processes directly affect the quality of performance. Now the market ceramic used is mainly in 25 × 25,18 × 18,15 × 15,12 × 12. Ceramic chip area is larger, the larger the dielectric constant, the higher the resonant frequency and the better is the receiving. Most of the ceramic wafer design is square, to ensure that the resonance in the XY direction is consistent, in order to achieve signal receiving well-distributed. 
 
Silver Plate: the silver layer of ceramic antenna can affect the resonant frequency. Ideal frequency of GPS ceramic should fall 1575.42MHz on the nose, but the antenna frequency is vulnerable to affect by the surrounding environment, especially built in the machine, Therefore, have to adjust the silver-coated form, to make sure the frequency remained at 1575.42MHz .

 
The Feed Point: ceramic antenna collects resonance signal through the feed point and then sent to the backend. Since the antenna impedance matching reasons, feed is generally not in the center of the antenna, but doing minor adjustments in the XY direction. This impedance matching method is simple and has no extra cost. Move only in the uniaxial direction is called a single partial antenna, do move in two axes are referred to as double-side. 

 
The amplifier circuit: to bear the shape and size of the PCB ceramic antenna. As GPS has the characteristics of ground bounce, when the background is 7cm × 7cm without a break earth, patch antenna performance can be to the limits. Although restriction by the appearance of the exterior structure and other factors, but try to maintain a considerable size and the same shape. Amplifier gain selection should be with the back-end LNA gain. Before the required signal input of Sirf’s GSC3F, total gain shall not exceed 29dB, otherwise saturated signal will result in self-excited.

Quick demonstration showing how an oscilloscope, an RF signal generator and a simple box with 5 resistors (3 – 50R0 and 2 – 1K0) can be used to observe antenna resonant frequency in the 7 MHz range. Note: This is no substitute for an Agilent VNA, but then, it isn’t going to cost as much either if this GPTE (General Purpose Test Equipment eg scope, signal gen) are just sitting around idle … More info (schematic of resistors in ‘magic box’, calculation of impedance using values read off O-scope): web.archive.org .
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