# Research on the Positioning Performance of GNSS with a Low-Cost Choke Ring Antenna
## 1 Introduction  
One of the key features of all measurement systems, including GNSS (Global Navigation Satellite Systems), is the accuracy of their operation, which can be assessed based on the analysis of measurement errors. The mentioned errors can be systematic, i.e., repeated with each measurement, or can be random for individual measurements. Manufacturers try to minimize systematic errors at an early stage of design. Systematic errors include, for example, receiver clock errors, which are effectively eliminated through the use of compensation methods. On the other hand, most of the observed errors in GNSS result from the operation of random factors, the description of which requires the use of mathematical statistics methods [1, 2]. The key aspect in the analysis of the operation of satellite systems is the propagation conditions of the radio signal. They are related to, among others, the following phenomena affecting the damping of radio waves: covering the wave by buildings and trees, reflections of radio waves from various types of surfaces, and multipath wave propagation [3]. The factors obscuring the horizon include, among other buildings, that are an obstacle to the propagating wave, reducing its energy level. In turn, possible reflections and multipath of the radio signal are a direct cause of radio wave fading. It is a common phenomenon, the negative impact of which can be minimized by, inter alia, the use of several transmission frequencies in the receiver, the use of the special design of antennas, or the development of data processing algorithms in the receiver [3]. Most modern GNSS receivers already use at least two transmission frequencies and have an extensive signal processing layer. They also have external antennas, which makes the development of the antenna design the most available method of minimizing the reflection and multipath phenomena among the other mentioned options [4]. Several different antennas are used in GNSS: from small patch antennas (car navigation) to complex geodetic antennas [5; 6]. There are also antennas for special applications, which have mostly larger dimensions, allowing them to obtain a sealed structure and the highest possible resistance to adverse environmental phenomena [7; 8; 9]. These types of antennas include choke ring antennas, which enable high damping of signals arriving at low or negative elevation angles [10; 11; 12]. For this purpose, the discussed antennas use coaxial rings (quarter-wave chokes) with a specially selected depth (usually \(\frac{1}{4}\) wavelength of the antenna operating frequency) [13]. One of the advantages of such a structure is that it prevents the transverse flow of the induced electric current, which also allows the active element of the antenna to be electrically isolated from the side walls. In addition, this type of antenna significantly increases the protection of the receiver against jamming and interference from other radio devices nearby. Their main disadvantage is usually heavy weight resulting from the need to use metal (often steel) as the material from which the ring cover is made [5]. Localized effects such as multipath result from the environment around the receiving antenna [14]. Position fix errors are mainly caused by multipath propagation of GNSS signals. Providing a clear and accurate signal to a GNSS receiver is the primary purpose of the antenna. Integrated choke ring antennas are commercially available and very expensive [15; 16]. Leica, among others, publishes the results of localization scatter studies for the AR25 choke ring antenna [17], which indicate a slight standard deviation of the obtained results (Easting 1.1 [mm], Northing 1.3 [mm], Height 2.5 [mm]) and confirms the high repeatability of positioning. Research work on choke ring antennas also focuses on the design of miniaturized [10] and increasingly lighter versions of antennas [18]. Most often, choke ring antennas are composed of deep concentric rings on a flat circular metal ground plane [11].