1. Background
The microwave and millimeter wave (hereinafter referred to as microwave) products mentioned in this article mainly refer to passive antennas and devices working in the 4-86GHz frequency band. They enable the communication system to have a high dynamic range and realize broadband analog channel transmission without the need for a power module. They are the core antenna feeder components in modern point-to-point wireless communication systems. The article first introduces the relevant terms of microwave antennas and devices, aiming to explain the relationship between core indicators and system performance; microwave products have a wide range of frequency bands, and this article mainly explains the categories of microwave antennas and devices currently on the market from different perspectives And some technical concerns and characteristics when selecting models. Considering that microwave technology has been commercialized for a short time, it can be said that it is an emerging industry in China. Many companies have only equipped with comprehensive microwave and millimeter wave test equipment in the past 10 years. Therefore, the products and technologies are still not perfect. This article will extract a chapter Discuss the future industrial development trend of microwave technology.
2. Fundamentals on Microwave Antennas and Components
Understanding any product requires first understanding the characteristics of these products, the different indicators and how good or bad indicators affect the use of the product. For point-to-point wireless communication systems, the quality of the product affects the gain, efficiency, link interference and service life of the system. This chapter analyzes some general terms and their relationship with point-to-point wireless communication systems from the perspective of antennas and devices.
2.1 General Terminologies for Antennas
Table 1 lists common terms for antennas and their potential impact on system performance. As the core device that converts energy into free-space wireless electromagnetic energy, the antenna’s radiation characteristics are the most critical indicators. Figure 1 lists several core indicators used to describe the antenna’s radiation characteristics. In addition to the gain, the front-to-back ratio and the radiation envelope The network diagram is the two most concerned indicators in the selection of point-to-point communication antennas.
Table 1 The relationship between conventional terms and systems of microwave antennas
2.2 General Terminologies for Components
Table 2 lists device general terms and their potential impact on system performance. Among them, difference loss and isolation are often the two most concerned indicators in the selection of point-to-point microwave devices. When the device is cascaded with the antenna, they directly affect the gain of the antenna feed system and the cross-polarization characteristics of the pattern.
Table 2 General terminology and system relationship of microwave devices
2.3 General Terminologies for Stabilities
We regard product reliability as an indispensable part of the product index. Table 3 lists the reliability and environmental adaptability experimental terms related to antennas and devices in point-to-point communication. Their quality is directly related to the service life of the communication system or Component maintenance cycle.
Table 3 Common terms for product reliability of microwave antennas and devices
3. Microwave Antenna Classification and Selection Microwave Antennas Classifications
Microwave antennas can be classified from multiple perspectives. This article aims to analyze the following five conventional classification methods in the industry.
3.1 According to Frequency and Size Classification According to Frequency and Size
The most common and widely recognized classification methods for microwave antennas are frequency bands and antenna sizes, which are basically used by antenna manufacturers to define their product numbers. Table 4 is the corresponding table of frequency bands and sizes of products of Tongyu Communication Co., Ltd. (where green, light green and red represent products released in different years from 2011 to 2013), and Table 5 is the frequency band definition of each frequency. It is worth mentioning that although the microwave antenna covers 4-86GHz, the large-aperture antenna does not cover the entire frequency band. This is mainly because the large-aperture antenna is generally used for long-distance microwave transmission. In addition, the higher the frequency, the narrower the beam width, and the large-aperture antenna with too high frequency will also make link alignment a problem. In addition, the traditional microwave antenna has a bandwidth of about 10%. Recently, Tongyu has begun to launch a 20% broadband antenna. This is why some frequency points in Table 5 include narrow-band and wide-band specifications.
Table 5 Microwave Antenna Frequency List
3.2 According to polarization classification According to Polarization
Polarization is a major characteristic of electromagnetic fields. Using orthogonally polarized signals in a communication channel doubles the channel capacity while keeping the frequency band constant. At present, point-to-point microwave systems are divided into three types according to polarization: single polarization, dual polarization and circular polarization. Among them, the first two are relatively mature, and dual polarization microwave antennas are widely used in XPIC microwave communication systems. Figure 2-Figure 3 are two single-polarization and dual-polarization microwave antenna products produced by Tongyu Company. It is worth noting that dual-polarized products can be considered as a combination of single-polarized products and orthogonally polarized couplers.
3.3 Classification according to performance level According to Level of Performance
According to the different Paul characteristics of the antenna pattern and the antenna performance parameters described in 2.1, different countries have formulated different standards to describe the level and difference of microwave antennas. The most common ones are the ETSI standard of the European Telecommunications Standards Institute, the FCC standard of the US Federal Communications Commission, the ANATEL standard of the Brazilian National Telecommunications Agency, the ACMA standard of the Australian Communications and Media Authority, and the IC standard of the Canadian Department of Industry. The most commonly used in the industry is the ETSI standard, which sets Class1-Class4 levels for the level of the point-to-point antenna radiation envelope. The best-selling point-to-point microwave antennas currently on the market belong to Class 2-3 levels, while Class 4 antennas have higher front-to-back ratios and RPE requirements, and have become the next-generation products actively developed by major manufacturers. Figure 4-Figure 5 shows the test results of the radiation pattern of the Class3 (referred to as C3) and Class4 (referred to as C4) antennas developed by Tongyu Communication Co., Ltd. It can be seen that to meet these international standards, the antenna must first make its pattern curve lower than the upper limit of the C3 and C4 Paul lines specified by ETSI. Compared with the C3 antenna, the C4 antenna requires a lower antenna pattern and a higher front-to-back ratio, which allows users to deploy more microwave antennas within a limited space.
Of course, different standards also have different classification methods. For example, FCC, IC or ACMA have two grades of A and B respectively. Antenna manufacturers fully demonstrate 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 Company. Antennas that meet ETSI Class 3 and FCC levels use the ultra-high performance antenna code 'U', and antennas that meet ETSI Class 4 levels use the high-performance antenna code 'E' ' to indicate that they respectively represent C3 and C4 single-polarized antennas with 0.6m aperture and working at 38GHz.
3.4 Classification According to Application Scenarios
The application scenarios of microwave antennas are divided into electrical scenarios and environmental scenarios. The electric scene refers to the occasion where the microwave antenna is used to build a radio link, which is divided into point-to-point (p2p) microwave antenna and point-to-multipoint (p2mp) microwave antenna. Due to its different application occasions, the requirements for the radiation characteristics of microwave antennas are also different. For example, microwave antennas used to replace single-point-to-single-point transmission of optical fibers must have a three-dimensional pattern similar to that of a pencil beam, and a two-dimensional section pattern must have the effect shown in Figure 1. The characteristics of the microwave antenna used for multi-point coverage are similar to the conventional base station antenna, and the purpose is to realize signal broadcasting in a large angle range. Therefore, the three-dimensional pattern of the microwave antenna of p2mp must have the characteristics of a fan beam, and its two-dimensional direction The picture must have the effect shown in Figure 6 and Figure 7.
According to environmental scenarios, microwave antennas are mainly divided into three types: ordinary antennas, high-corrosion-resistant antennas and high-wind-resistant antennas. The latter two are mainly for special application places such as seaside with high smog corrosion or areas with high incidence of hurricanes, which require special high anti-corrosion surface treatment or structural reinforcement design.
3.5 According to Radio Interface Classification According to Radio Interface Types
In a complete microwave link communication system, more important than the antenna is the outdoor active wireless transmitter receiver, also known as Radio. In order to match their products with radios from different manufacturers, antenna manufacturers often equip them with special structural connectors or antenna matching transition units. When users purchase antennas, they often classify antennas according to different Radio types. Figure 8-Figure 10 are schematic diagrams of antenna interfaces of three different manufacturers. It is worth noting that, for antenna performance, since most of the components are shared, the performance of the antenna is generally considered to be unchanged by the change of the interface.
4. Microwave Component Classification and Selection Microwave Component Classifications
Microwave devices can also be classified from multiple perspectives. This article aims to discuss the following four conventional classification methods in the industry.
4.1 Polarization separation category According to Polarization
The polarization separation device itself is also a polarization coupling device. Common such devices include microwave orthogonal polarization coupler (OMT) and polarizer (Polarizer). The former has been widely used in commercial microwave communications. It mainly includes two types: separate type and direct buckle type. The separate type is mainly connected to the flexible waveguide through a standard flange. The cost of the device is low but the cost of the overall system accessories is relatively high; The main purpose is to allow the outdoor unit (ODU) or Radio to be directly connected to the device, thus saving the expensive flexible waveguide. Figure 11 is a schematic diagram of the polarization separation field distribution of the device in the state of receiving dual-polarization signals. Utilizing similar principles, Tongyu has successfully developed full-band separation and direct coupling OMT products (see Figure 12).
4.2 According to Power Division
Common microwave devices in the power distribution category are power dividers and directional couplers. They both have the characteristics of distributing or combining power, but there are essential differences. The former divides a signal into multiple channels according to a specific amplitude or phase, which is common in the excitation array antenna unit; while the latter generally refers to a 4-port device, and its two output ports generally do not work at the same time, giving the link a backup Function. The latter product is commonly used in point-to-point microwave communication systems, and is used at the back end of microwave antennas to improve link reliability. Figure 13-14 is the high-performance microwave directional coupler and its antenna connection effect diagram developed by Tongyu Company.
4.3 Frequency Classification According to Frequency Division
Frequency classification microwave devices mainly refer to products such as microwave filters, microwave duplexers, multiplexers and outdoor branch units. These devices are mainly integrated inside the antenna outdoor unit for functions such as filtering and channel integration. Microwave filters are mostly used for single-channel filtering. Duplexers enable link transmission and reception to share one antenna, while multiplexers and outdoor branch units can complete multi-channel fusion so that a single point-to-point link can achieve ultra-wideband transmission. Figure 15-16 demonstrates a custom duplexer and its performance.
4.4 Functional classes According to Functionalities
For several miniaturized microwave communication systems, multifunctional integrated microwave devices have become more and more common. For example, a device that integrates an orthogonally polarized coupler and a duplexer has been adopted by many radio manufacturers; in order to realize the multiplexing function, cascade connection of multiple filters and circulators is also a common solution. Here is a four-port coupling device independently developed by Tongyu Company. As shown in Figure 17, this product has four ports for connecting four outdoor units, and the other port is connected to a dual-polarized microwave antenna. The device integrates an orthogonally polarized coupler and two directional couplers, enabling each polarization of the XPIC system to have a backup function. Figure 18 is an antenna feeder system built with this device.
Development Trend of Microwave/Milimeter-wave Antennas and Components Development Trend of Microwave/Milimeter-wave Antennas and Components
Microwave and millimeter wave antennas and devices have the following future development trends: high performance, low cost, multi-polarization, broadband, high efficiency, miniaturization, custom integration, and high frequency. It is worth mentioning that with the development of LTE system and future 5G, small base station systems will become more and more common, and the number of microwave links in a unit space will become more, which requires the performance of microwave antennas and devices The price is higher and the price is lower; in addition, multi-polarization, broadband, and high frequency are mainly to meet the increasing demand for system bandwidth; more and more new outdoor units, in order to reduce the size of the entire system, Radio manufacturers have already Cooperating with antenna manufacturers to develop miniaturized and customized integrated antenna systems, which makes future microwave outdoor antenna feeder systems tend to be personalized and customized.
V. Summary
To sum up, this paper introduces passive microwave and millimeter wave antennas and devices in point-to-point wireless communication, discusses the existing product architecture around the performance and characteristics of these products, and briefly describes the development trend of this industry.
author:
Dong Junwei, Ph.D., graduated from the Department of Electrical Engineering of Virginia Tech in 2009. From 2009 to 2011, he was employed by the American Microwave Engineering Company as a research scientist. A returnee in September 2011, he is currently the chief technology deputy director of Tongyu Communications Co., Ltd., and is also responsible for the management and operation of the microwave department.
Wu Zhonglin, chairman of Guangdong Tongyu Communication Co., Ltd. In 1989, he graduated from Xidian University; in 1994, he successfully developed the first domestic mobile communication base station antenna, breaking the situation that the Chinese base station antenna market was monopolized by foreign products; in 1996, Tongyu Communication Company was registered and established.
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