Microwave antenna based on point-to-point communication and its high-precision far field test system

Introduction: Compared with optical fiber communication, microwave point-to-point communication has many advantages such as good portability, high cost performance, and no land property rights. In many countries, they have become an alternative technology for fiber-optic connections between base stations. For example, in the United States, the United Kingdom, Japan and other countries, more than 85% of base station backhaul communications have been used by operators.

Compared with optical fiber communication, microwave point-to-point communication has many advantages such as good portability, high cost performance, and no land property rights. In many countries, they have become an alternative technology for fiber-optic connections between base stations. For example, in the United States, the United Kingdom, Japan and other countries, more than 85% of base station backhaul communications have been used by operators. The survey shows that the annual demand for microwave antennas worldwide is growing at a rate of about 10% per year. In addition, the demand for wireless broadband access in public places such as shopping malls, parks, and stations is becoming more and more popular. Small base stations have become popular solutions. The latter end-to-point backhaul scheme of this type of communication system can also use microwave antennas. Both provide a good market prospect for microwave antennas and peripheral devices. The microwave antennas mentioned in this paper mainly refer to passive antennas operating in the 4 to 86 GHz band. They enable communication systems to have high dynamic range and broadband analog channel transmission without the need for power modules, and are core antenna components in modern point-to-point wireless communication systems.

Arranging as many microwave antennas as possible in as little space as possible requires very strict requirements for mutual interference between the antenna and the antenna, and imposes high requirements on the accuracy and dynamic range of the test system. In general, the main antenna parameters that measure this mutual interference are front-to-back ratio, side lobes and patterns. This paper focuses on the high-precision microwave antenna far-field test system of Guangdong Tongyu Communication Co., Ltd., and gives some test results with Eband ETSI Class4 antenna.

Microwave antennas can be classified from multiple angles. The general industry has the following classification methods.

2.1 Classification to Frequency and dimension by frequency and caliber

Microwave antennas are the most common and commonly accepted industry classifications for frequency bands and antenna diameters. Antenna manufacturers also use this to define their product codes. Table 1 shows the band definitions for each frequency. Table 2 is the product frequency band and size correspondence table that has been successfully developed by Tongyu Communication Co., Ltd. and can be supplied in large quantities. It is worth mentioning that although the microwave antenna covers 4-86 GHz, large aperture The antenna is not covered by the full frequency band. This is mainly because the large-diameter antenna is generally used for long-distance microwave transmission. As the frequency increases, the spatial loss becomes difficult to reflect the advantage of large-caliber and high-gain. In addition, the higher the frequency, the narrower the beam width is, and the height is too high. Large-caliber antennas with frequencies also make link reversal a problem. In addition, the traditional microwave antenna has about 10% of the bandwidth. Tongyu Communications has launched 20% of broadband antennas, including 5W, 6W, 7W, 10W, 23W and 27W.

Table 1 Microwave antenna frequency

Table 2 List of antennas by frequency band and aperture

2.2 Classification by Polarization to PolarizaTIo n

Polarization is a major characteristic of electromagnetic fields, and the use of orthogonal polarization signals in the communication channel allows the channel capacity to be doubled in the case of a constant band. At present, the point-to-point microwave communication system is divided into single polarization and dual polarization according to polarization. The first two are relatively mature. Figure 1 and Figure 2 are two single-polarized and dual-polarized microwave antennas produced by Tongyu. product.

2.3 Classification to Level of Performance by Performance Level

Different countries have developed different standards to describe microwave antenna levels and differences based on antenna pattern characteristics. The most commonly used in the industry is the ETSI standard, which sets the Class1-Class4 level for the level of the point-to-point antenna radiation envelope. The best-selling point-to-point microwave antennas on the market belong to Class 3, while Class 4 antennas have higher front-to-back ratio and pattern envelope requirements, and have become the next generation products actively developed by major manufacturers. Figures 3 and 4 show the results of the radiation pattern test of the Class 3 and Class 4 antennas developed by Tongyu Communication Co., Ltd. It can be seen that the antenna is full of ETSI standards, and its pattern curve is lower than the upper limit of the Class 3 and Class 4 envelopes specified by ETSI. Compared to the Class3 antenna, the Class4 antenna requires a lower antenna pattern and a higher front-to-back ratio, which allows a larger number of microwave antennas to be deployed in a limited space.

Antenna manufacturers are fully demonstrating the performance of their antennas to meet the needs of customers around the world for different markets. For example, TYA06U38S and TYA06E38S are two microwave antenna products of Tongyu. The antennas that meet the ETSI Class 3 level use the ultra-high performance antenna code 'U', and the antennas that meet the ETSI Class 4 level use the different high-performance antenna code 'E'. They represent C3 and C4 single-polarized antennas operating at 38 GHz with a diameter of 0.6 m.

2.4 Classification to ApplicaTIon Scenarios by Application Scenario

Figure 7 point-to-multipoint fan antenna

The application scenario of the microwave antenna mainly refers to the electrical scene, which refers to the occasion where the microwave antenna is used to construct a radio link, and is divided into a point-to-point (p2p) microwave antenna and a point-to-multipoint (p2mp) microwave antenna. Due to the different applications, the microwave antenna has different radiation characteristics. For example, microwave antennas for single-point-to-single-point transmission, such as fiber optics, have a three-dimensional pattern that has a pencil beam-like characteristic, and the two-dimensional section pattern needs to have the same as shown in FIG. 3 or FIG. effect. The microwave antenna used for multi-point coverage has the same characteristics as the conventional base station antenna, and the purpose is to realize signal broadcast in a large angle range. Therefore, the three-dimensional pattern of the microwave antenna of the p2mp should have a fan beam characteristic and its two-dimensional direction. The figure must have the effects shown in Figures 5 and 6. Figure 7 is a sector antenna designed by Tongyu Communications for point-to-multipoint communication.

3.1 System Requirements

It is more difficult to test the previously mentioned C4 antenna and Eband (80 GHz) antenna using the traditional microwave darkroom test system, because they put forward higher requirements on the dynamic range and accuracy of the system compared to the traditional test system. . In order to derive the general requirements of the system requirements, we will use the following Eband Class-4 antennas as a detailed description:

Antenna diameter: φ=0.6m

Operating frequency: 71GHz-86GHz

Half power angle: 0.5 degrees

Gain: 50dBi

Before and after ratio: 70dB

Define the amplitude tolerable amount σ to be the maximum

3.2 system design

1) System block diagram

As shown in Figure 8, it is a block diagram of the system that uses the signal source, the most typical far field test system architecture of the spectrum analyzer. The transmitting end is placed on the ground, the receiving end and the central control system are placed on the top of the 7-story building. The line of sight (LOS) at both ends forms an angle with the ground. This is very advantageous for testing the antenna with high front-to-front ratio because the antenna can Directly against the sky.

Figure 8 system block diagram

2) System hardware

As shown in Fig. 9(a), respectively, the transmitting end bracket and the signal source are shown in Fig. 9(b) as the receiving end turntable, and Fig. 9(c) is the receiving end some equipment.

Figure 9 system hardware

3) System software

Like other test systems, software design requires precise control of its motors, spectrum analyzers, etc., requiring fast and efficient calculation of test data and final display. For the current test system, there are two highlights worth mentioning. The first is that all four axes support "absolute mode", "relative mode" and "normalized mode", and can be freely and independently controlled. As shown in Figure 10; the second is to design a remote spectrum analyzer control system for testing antennas with extremely high front-to-back ratio or extremely high dynamic range for testing. This design allows the spectrum analyzer to remotely obtain RF transmission loss and Correct the parameters as shown in Figure 11.

3.3 Test examples

The test system described above has been successfully developed and put into use in Guangdong Tongyu Communication Co., Ltd., which can effectively test the current ETSI Class3 antenna and the future ETSI Class 4 antenna. In the test, it was found that the accuracy can be greater than 75 dB before and after, and the half power angle is less than 0.5 degrees. As shown in Fig. 12(a), a pattern test result of a 0.3 m Class 4 antenna at 86 GHz is shown in Fig. 12(b) as a pattern test result of a 86 GHz 0.3 m Class 3 antenna.

Figure 12 test results

In summary, this paper introduces passive microwave antennas and high-precision far-field test systems in point-to-point wireless communication, introduces the performance and classification methods of these products, introduces the architecture and hardware and software components of high-speed remote test systems, and Describe the development trend of the industry.