Analysis of GPS Antenna Principle

　　At present, the GPS receiver circuit in practical application is generally composed of four parts: antenna unit, radio frequency unit, communication unit and calculation unit. Based on the analysis of the composition of GPS satellite signals, this paper gives the principle and application of the radio frequency front-end GP2010.

　　1. Composition of GPS satellite signals

　　The GPS satellite signal is synthesized by typical code division multiple access (CDMA) modulation technology, and its complete signal mainly includes three components: carrier, pseudo-random code and data code. The signal carrier is in the L-band, and the center frequencies of the two carriers are denoted as L1 and L2, respectively. The satellite signal reference clock frequency f0 is 10.23MHz, and the center frequency of the signal carrier L1 is 154 times the frequency of f0, namely:

　　fL1=154×f0=1575.42MHz (1)

　　Its wavelength λ1=19.03cm; the center frequency of the signal carrier L2 is 120 times the frequency of f0, namely:

　　fL2=120×f0=1227.60MHz (2)

　　2. Analysis of GPS Antenna Principle

　　Its wavelength λ2=24.42cm. The frequency difference between the two carriers is 347.82MHz, which is about 28.3% of L2. The carrier frequency is selected in this way to measure or eliminate the propagation delay error caused by the ionospheric effect when the navigation signal propagates from the GPS satellite to the receiver. Pseudo-random noise code (PRN), that is, ranging code, mainly includes two kinds of fine ranging code (P code) and coarse ranging code (C/A code). The code rate of the P code is 10.23MHz, and the code rate of the C/A code is 1.023MHz. The data code is the navigation and positioning data sent by the GPS satellite to the user receiver in binary form. It is also called the navigation message or D code. It mainly includes satellite calendar, satellite clock correction, ionospheric delay correction, working status information, and C/A code conversion. To capture the information of the P code and the general ephemeris of all satellites; the total message consists of 1500 bits, divided into 5 subframes, each subframe transmits 10 words within 6s, each word 30 bits, a total of 300 bits, so the data The baud rate of the code is 50bps.

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