1. Ceramic flakes: The quality of ceramic powder and sintering process
directly affect its performance. The main ceramic chips currently used on the
market are 25 × 25, 18 × 18. 15 × 15. 12 × 12. The larger the area of the
ceramic sheet, the greater the dielectric constant, the higher the resonance
frequency, and the better the acceptance effect. Ceramic chips are mostly square
in design to ensure consistent resonance in the XY direction and achieve uniform
star collection.
2. Silver layer: The silver layer on the surface of a ceramic antenna can
affect the resonance frequency of the antenna. The ideal GPS ceramic chip
frequency point is accurately set at 1575.42MHz, but the antenna frequency point
is very susceptible to the influence of the surrounding environment, especially
when assembled in the entire machine. It is necessary to adjust the silver
coating shape to maintain the frequency point at 1575.42MHz again. Therefore,
GPS equipment manufacturers must cooperate with antenna manufacturers when
purchasing antennas and provide complete machine samples for testing.
3. Feed point: The ceramic antenna collects resonance signals through the
feed point and sends them to the backend. Due to antenna impedance matching, the
feed point is generally not in the center of the antenna, but slightly adjusted
in the XY direction. This impedance matching method is simple and does not
increase the cost. Moving only in the single axis direction is called a single
biased antenna, and moving on both axes is called a double biased antenna.
4. Amplification circuit: The shape and area of the PCB carrying the
ceramic antenna. Due to the characteristic of ground bounce in GPS, when the
background is 7cm × When the ground is 7cm uninterrupted, the efficiency of the
patch antenna can be maximized. Although constrained by factors such as
appearance and structure, try to maintain a considerable area and uniform shape.
The selection of amplification circuit gain must be coordinated with the backend
LNA gain. The GSC3F of Sirf requires that the total gain before signal input
should not exceed 29dB, otherwise the signal Supersaturation will generate self
excitation.
GPS antenna has four important parameters: Gain, VSWR, Noise figure, and
Axial ratio. Among them, special emphasis is placed on the shaft ratio, which is
an important indicator to measure the difference in signal gain of the entire
machine in different directions. Due to the random distribution of satellites in
the hemisphere sky, it is crucial to ensure that the antenna has similar
sensitivity in all directions. The axial ratio is affected by antenna
performance, external structure, internal circuit of the entire machine, and
EMI.
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