Overview of the development of GNSS high-precision antennas

introduction

With the continuous development and improvement of satellite positioning technology, high-precision positioning technology has been used in all walks of life in modern life. For example, in fields such as surveying and mapping, precision agriculture, drones, and unmanned driving, high-precision positioning technology can be seen everywhere. Especially with the completion of the networking of Beidou's new generation satellite navigation system and the arrival of the 5G era, the continuous development of Beidou + 5G is expected to promote the application of high-precision positioning technology in airport dispatching, robot inspection, vehicle monitoring, logistics management and other fields. The realization of high-precision positioning technology is inseparable from the support of high-precision antennas, high-precision algorithms and high-precision boards. This article mainly introduces the development and application of high-precision antennas and the current status of technology.

1. Development and application of GNSS high-precision antennas

1.1 Introduction to high-precision antennas
In the field of GNSS, high-precision antennas are a type of antenna that have special requirements for the stability of the antenna phase center. They are usually used in conjunction with high-precision boards to achieve centimeter- or millimeter-level high-precision positioning. In the design of high-precision antennas, there are usually special requirements for the following indicators of the antenna: antenna beam width, low elevation gain, out-of-roundness, roll-off coefficient, front-to-back ratio, multipath resistance, etc. These indicators will directly or indirectly affect the phase center stability of the antenna, thereby affecting the positioning accuracy.

1.2 Application and classification of high-precision antennas
High-precision GNSS antennas were initially mainly used in the field of surveying and mapping to achieve static millimeter-level positioning accuracy in engineering stakeout, topographic mapping, and various control measurement processes. As high-precision positioning technology becomes increasingly mature, high-precision antennas are gradually used in more and more fields, including continuously operating reference stations, deformation monitoring, earthquake monitoring, surveying and mapping, drones, precision agriculture, autonomous driving, driving test and driving training, engineering machinery and other industrial fields. The index requirements for antennas in different applications are also significantly different.

1.2.1 CORS system, deformation monitoring, earthquake monitoring-reference station antenna
When high-precision antennas are used in continuously operating reference stations, accurate position information is obtained through long-term observations, and the observation data is transmitted to the control center in real time through the data communication system. The control center calculates the error correction parameters in the area and then sends the error information to the rover (user end) through the ground-based enhancement system, wide-area enhancement system, satellite-based enhancement system, etc., ultimately allowing the user to obtain accurate coordinate information [1].In applications such as deformation monitoring and earthquake monitoring, it is necessary to accurately monitor the amount of deformation and detect tiny deformations to predict the occurrence of natural disasters.Therefore, in the design of high-precision antennas in applications such as continuously operating reference stations, deformation monitoring, and earthquake monitoring, the first thing that must be considered is its excellent phase center stability and anti-multipath interference capabilities, so that accurate position information can be provided in real time for various enhancement systems. In addition, in order to provide as many satellite correction parameters as possible, the antenna must receive as many satellites as possible, and the four-system full-band configuration has become a standard configuration. In such applications, a reference station antenna (base station antenna) covering the full frequency band of the four systems is usually used as the observation antenna of the system.

1.2.2 Measurement and mapping-built-in measurement antenna
In the field of measurement and mapping, it is necessary to design a built-in measurement antenna that is easy to integrate. The antenna is usually built on the top of the RTK receiver to achieve real-time high-precision positioning in the field of measurement and mapping.The main considerations in the design of built-in measurement antennas include frequency band coverage, beam coverage, phase center stability, antenna size, etc. Especially with the popularization of network RTK applications, full-network built-in measurement antennas that integrate 4G, Bluetooth, and WiFi have gradually occupied a major share of the market. Since their launch in 2016, they have been favored by the majority of RTK receiver manufacturers and have been widely used and promoted.
1.2.3 Driving test and driving training, driverless driving - external measurement antenna
The traditional driving test system has many disadvantages, such as high investment cost, high operation and maintenance costs, large environmental impact, low accuracy, etc. After high-precision antennas are applied to the driving test system, the driving test system changes from manual judgment to intelligent judgment, with high judgment accuracy, which greatly reduces the human and material costs of the driving test.In recent years, unmanned driving systems have developed rapidly. In unmanned driving, positioning technology that combines RTK high-precision positioning and inertial navigation is usually used, which can achieve high positioning accuracy in most environments.In driving test driving training, driverless driving and other systems, the form of external measurement antenna is often used, which requires the antenna to have multi-system and multi-frequency working frequency bands, be able to achieve higher positioning accuracy, have a certain ability to suppress multipath signals, and have good environmental adaptability, and can be used in outdoor environments for a long time without failure.

1.2.4 Drone-high-precision drone antenna
The UAV industry has developed rapidly in recent years. UAVs have been widely used in agricultural plant protection, surveying and mapping, power line inspection and other scenarios. In such scenarios, only high-precision antennas can ensure the accuracy, efficiency and safety of various operations. Since drones have the characteristics of fast speed, light load, and short endurance, the design of high-precision drone antennas mainly focuses on factors such as weight, size, and power consumption, and achieves as wideband a design as possible while ensuring weight and size.

2. Current status of GNSS antenna technology at home and abroad

2.1 Current status of foreign high-precision antenna technology
Foreign research on high-precision antennas began earlier, and a series of high-precision antenna products with better performance have been developed, such as NoVatel's GNSS 750 series choke coil antennas, Trimble's Zepryr series antennas, Leica AR25 antennas, etc., among which there are many innovative antenna forms. Therefore, for a long time in the past, my country's high-precision antenna market was dominated by foreign products. However, in the past ten years, with the rise of a large number of domestic manufacturers, foreign high-precision GNSS antennas have basically no advantages in performance. Instead, domestic high-precision manufacturers have begun to expand markets abroad.In addition, some new GNSS antenna manufacturers have developed abroad in recent years, such as Maxtena, Tallysman, etc. Their products are mainly small GNSS antennas used in drones, vehicles and other systems. The antenna form is usually a high dielectric constant microstrip antenna or a four-arm helical antenna form. Foreign manufacturers no longer have an advantage in the design technology of this type of antenna, and domestic and foreign products are entering a period of homogeneous competition.