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At present, the mainstream domestic positioning system using GPS (Global Positioning System) and BeiDou positioning system, its civil band are used L1 band (center frequency 1575.42MH), the advantages and disadvantages of the GPS antenna PCB design directly affects the transmission of signals and the number of star search. The following is a brief description of the GPS antenna design of small knowledge.
1, GPS antenna active circuit
Active antenna, as the name implies is that the antenna needs external power supply, the power supply of the antenna is not the same as our usual power supply, because the signal line of the active antenna is not only power supply, but also need to pass the signal. If the power supply is directly connected to the antenna's power supply through wires, the signal will flow back to the power supply through the wires, resulting in weakening or loss of signal.
Please note:
If the power supply wire is directly connected to the antenna's signal wire, it will cause the signal to flow back to the power supply, weakening the signal or causing it to be lost.
The paving on both sides of the signal line should form a good backflow, add some over holes on both sides of the signal line to form a complete connection with the bottom GND layer.
GPS antenna power supply and signal directly are generally connected to a 27nH inductance (according to the frequency of different inductance value is also different), inductance through the intersection of straight resistance, will block the signal to the power supply "loss".
GPS antenna
2, 50 ohm characteristic impedance
50 Ohm impedance means the impedance from the input of GPS antenna to the input of GPS chip (no break in the wire) (if there is a break in the wire between the two breaks, the impedance of the wire is 50 Ohm). Maintaining a 50 ohm characteristic impedance of the alignment is a very important thing, especially during the design of RF circuits, as the operating frequency is very high (GHz), the control of the characteristic impedance becomes even more important. If the characteristic impedance is not well controlled at 50 ohms, then it is easy to cause signal reflection and lack of signal integrity. Use software to calculate the impedance of the PCB in the design of the PCB.
In the use of CAD software to calculate the impedance of the PCB before and PCB manufacturers to determine the use of PCB materials PCB substrate thickness, copper foil thickness, etc.. In the PCB playing board should also be specified to do 50 ohm impedance of the wire, so that the PCB board factory will be impedance matching circuit to do processing, the effect will be more ideal.
Antenna as GPS equipment in the most important receiving device, it plays a role like human “ears”; is the satellite sent down the electromagnetic wave energy into electronic devices can be resolved current. Therefore, the performance of the antenna will be directly related to the performance of the GPS machine.
3, GPS antenna selection recommendations
(1) In the terminal structure space allows, can be unified to ensure that the GPS antenna face up the installation of the use of state; and there is no large metal objects around the case of blocking, it is recommended to use GPS ceramic antenna, in the case of space allows to try to choose a large size of the ceramic antenna.
(2) In the case that the terminal can not be guaranteed to be used, and the space is limited: such as cell phones, badges with positioning function; it is recommended to use FPC antenna.
(3) In the clear terminal installation environment is harsh, and the GPS performance has high requirements; it is recommended to use GPS active antenna 4, in can not guarantee the product installation and use of the state, but the space is not restricted, you can also choose similar to the GSM external rod antenna.
This is GPS antenna.