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As the global industry demands electronic products to be "light, thin, short and small", the miniaturization of GPS systems has become a trend, and the size of GPS antennas has become a bottleneck in the miniaturization design of GPS systems.
Most existing GPS antennas use ceramic substrate antennas or helical antennas [1] . Ceramic substrate antennas have the highest gain on the orthogonal plane of the radiating element, that is, the radiating element on the horizontal plane has the highest gain for the signal sent from the zenith. Therefore, ceramic substrate antennas are widely used in terminal products that are mainly facing upward, such as in car navigation devices.
Antennas with ceramic substrates as the medium are smaller in size, so GPS antennas are widely designed with ceramic substrates.
However, the ceramic substrate GPS antennas currently on the market have the following disadvantages that limit their practicality and scope of application in engineering:
1. The existing structure of ceramic substrate GPS antenna limits its further miniaturization;
2. The medium is thick, fragile and heavy;
3. Not resistant to high temperature, high processing cost;
4. Since the medium has a high dielectric constant, the consistency of the antenna during processing is not high, which affects the batch production yield and increases the manufacturing cost.
2 Analysis and new design of GPS antenna
2.1 Antenna Structure
The purpose of this design is to solve the shortcomings of the current ceramic substrate GPS antenna, such as fragility, poor temperature effect, high dielectric constant, poor consistency, high price, and difficulty in integration. A GPS antenna based on printed circuit board technology is proposed. It can reduce the weight and thickness of the antenna while ensuring that other electrical properties remain unchanged, thereby reducing the difficulty and cost of antenna processing.
The implementation is as follows:
The GPS antenna is designed according to the modified microstrip method . In order to solve the problem of large size of ordinary microstrip antenna, the structure of microstrip loop antenna is used in GPS design, and the impedance mismatch problem caused by the loop antenna is solved through the coupling feeding of the middle square patch. The antenna includes 1- dielectric layer, 2- loop antenna, 3- inverted T -slot, 4- coupling feeding patch, 5- metal floor and 6- metal floor.
As shown in FIG1 , a GPS antenna is constructed, comprising a dielectric layer 1 , an antenna floor 5 arranged on the first surface of the dielectric layer, and an antenna patch and a feeding point 6 arranged on the second surface opposite to the first surface of the dielectric layer, characterized in that the antenna patch comprises a loop antenna 2 arranged in a ring along the periphery of the second surface of the dielectric layer and a coupling feeding patch 4 arranged at intervals inside the loop antenna and adjacent to one side of the loop antenna , and the feeding point is arranged on the coupling feeding patch ; a T -shaped slot 3 is arranged in the middle of the loop antenna adjacent to the coupling feeding patch , the foot of the T -shaped slot is connected to the inner edge of the loop antenna, and the upper horizontal side of the T -shaped slot is parallel to the inner edge of the loop antenna. The coupling feeding proposed in the antenna solves the impedance mismatch problem caused by the loop antenna well, improves the impedance characteristics of the antenna while realizing miniaturization, and realizes the circular polarization characteristics of the antenna by opening an inverted T- shaped slot on the loop antenna, changes the commonly used method of cutting angle to realize microstrip circular polarization, and improves the consistency of the antenna during mass production. By selecting materials with low dielectric constants, compared to antennas with general ceramic substrates, the innovative structure reduces the size of the antenna while reducing costs, improving undesirable properties such as temperature resistance and fragility, and improving the consistency of mass production.
2.2 Antenna Performance Comparison
Compared with the prior art, the GPS antenna of this design has the following beneficial effects:
1. The antenna structure is further miniaturized. For example, when a ceramic substrate is used, the size of the GPS antenna of this design can be 17mm×17mm×4mm , which is only 46.2% of the size of the ordinary ceramic substrate GPS antenna ( 25mm×25mm×4mm ) (as shown in Figure 2 ) ; and when a low dielectric constant medium with εr = 2.65 is used , the size of the GPS antenna of this design can be 40mm×40mm×1mm , which is only 47.6 % of the size of the ordinary εr = 2.65 medium GPS antenna with 58mm × 58mm× 1mm ;
Figure 2 Traditional ceramic GPS antenna
As shown in Table 1 below :
Table 1
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medium
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This design GPS antenna
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Traditional GPS Antenna
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Area ratio
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ceramics
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17 x 17 x 4mm
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25 x 25 x 4mm
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46.2%
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εr =2.65 medium
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40 x 40 x 1mm
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58 x 58 x 1mm
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47.6%
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2. The GPS antenna of this design adopts low dielectric constant medium, which has good temperature effect and is not easy to break, thus solving the shortcomings of common GPS antennas such as poor temperature effect and fragility;
3. The GPS antenna of this design uses a common printed circuit board with a low dielectric constant, which reduces the cost and processing difficulty while improving the consistency of antenna batch processing;
4. The GPS antenna designed in this paper solves the shortcoming that the ceramic substrate GPS antenna is not easy to integrate with the circuit board. It uses printed circuit board technology to facilitate the integrated design with the GPS receiving link.
2.3 Antenna measurement results
The gain of the antenna in this design within the frequency band is measured by the comparison method and is shown in Table 2. The standard antenna in Table 2 is a standard circularly polarized helical antenna, and the antenna to be tested is a GPS antenna.
Table 2
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Frequency ( MHz )
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Antenna receiving level under test ( dB )
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Standard antenna reception level ( dB )
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Typical antenna gain ( dB )
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Antenna gain to be measured ( dB )
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1575
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-30.0
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-24.0
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10.0
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4.0
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The electrical performance of the GPS antenna can be reflected by the following test curves and measured directional diagrams:
Figure 3 Measured standing waves in the frequency band of the new GPS antenna and the H -plane radiation pattern at
1575MHz
The voltage standing wave ratio test results within the frequency band show that the voltage standing wave ratio of the antenna within the 1575MHz frequency band is less than 1.5 .
The test results of the antenna's radiation pattern at 1575MHz show that the antenna meets the pattern coverage requirements within the frequency band.
3. Comparison of advantages with traditional GPS antennas
Compared with the prior art, this design has the following advantages:
1. The antenna structure is miniaturized, with a volume of: length width height = 40mm 40mm 1mm .
By using loop antenna technology, the current is distributed along the loop, which forms a slow-wave radiation structure, which can resonate the frequency in a smaller size, and achieve better standing wave and radiation characteristics. And because of the low profile characteristics of the microstrip structure itself, its volume can be very small. And the rectangular patch coupling feeding method is adopted to solve the poor impedance matching of the loop antenna and the low efficiency of the matching network.
2. The antenna solves the shortcomings of common GPS antennas such as poor temperature effect and fragility.
The commonly used ceramic GPS antenna is very fragile due to the constraints of its own material properties, and it is very easy to crack due to uneven heating during high-temperature welding. When using printed circuit boards, the material itself is resistant to high temperatures, not easy to break, and has high strength, which greatly improves the structural performance parameters of the antenna.
3. The antenna uses a common printed circuit board with a low dielectric constant, which reduces the cost and processing difficulty while improving the consistency of antenna batch processing.
Ceramic materials have high dielectric constants and complex processing, so they have the disadvantage of poor consistency. Due to the high dielectric constant, its resonant frequency is very sensitive to size, and a small error during debugging may cause a large offset, which puts high tolerance requirements on actual production. When changing its structure, using a lower dielectric constant can also reduce the volume of the GPS antenna, which changes the shortcomings of high dielectric constant materials and improves product consistency. And because of the use of low dielectric constant materials, the cost is greatly reduced.
4. The antenna solves the shortcoming that ceramic substrate GPS antenna is not easy to integrate with the circuit board. It uses printed circuit board technology to facilitate integrated design with the GPS receiving link.
Because the processing technology is the same as that of the circuit board and is also based on PCB printed circuit technology, when a multi-layer microstrip structure is adopted, it is very easy to achieve an integrated design with the circuit board, with low design difficulty, high integration, low cost, and easy mass production.
5. The antenna has achieved the following indicators:
Frequency range: 1.575GHz ;
Voltage standing wave ratio: ≤ 1.5 ;
Gain: 4dB ;
Polarization: right-hand circular polarization;
Axis ratio: ≤ 1.5 ;
Weight: 10 g.
Since this design has the above advantages, it has wide promotion and application value.
4 Conclusion
The GPS antenna designed in this paper reduces the size and weight of the antenna while ensuring that other electrical properties remain unchanged, and reduces the difficulty and cost of antenna processing. It can be used in communication, detection , positioning , guidance and other fields. The proposed miniaturization technology and impedance matching technology can be extended and applied to the design of antennas in other frequency bands.
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提升卡
变色卡
千斤顶