Low-cost GNSS reflectometry measurement system with a dual-ridged horn antenna produced by a 3D printer and metal-coated

Abstract

The invention relates to a dual-ridged horn antenna structure covered with metal foil, produced by a three-dimensional (3D) printer, which is both cost-effective and linearly polarized, and is designed for directional use in GNSS-R measurement systems.

Description

[0001] LOW-COST GNSS REFLECTOMETRY MEASUREMENT SYSTEM WITH A DUALRIDGED HORN ANTENNA PRODUCED BY A 3D PRINTER AND METAL-COATED

[0002] TECHNICAL FIELD

[0003] The invention relates to a dual-ridged horn antenna structure covered with metal foil, produced by a three-dimensional (3D) printer, which is both cost-effective and linearly polarized, and is designed for directional use in GNSS-R measurement systems.

[0004] BACKGROUND

[0005] Traditionally, Global Navigation Satellite Systems (GNSS) technology is used for positioning studies. However, the disadvantage of this technique, known as multipath effects, has recently turned into an advantage by determining surface characteristics using SNR data. This method, referred to in the literature as GNSS-R (Reflectometry), allows the determination of surface characteristics such as sea level, snow depth, and soil moisture.

[0006] Geodetic GNSS antennas have a nearly hemispherical radiation pattern, making them less sensitive to reception from negative elevation angles. Despite their design, these antennas can still be used in GNSS-R applications since they cannot reject multipath signals at grazing incidence. However, such devices are relatively expensive, limiting the broader application of GNSS-R not only as a secondary role within Continuously Operating Reference Stations (CORS) networks but also as a primary tool for environmental monitoring. Therefore, in recent years, there has been a notable increase in the use of low-cost receivers for this method. Additionally, the directional use of geodetic GNSS antennas for GNSS-R applications remains an expensive solution.

[0007] The primary purpose of geodetic GNSS antennas is positioning rather than GNSS-R applications. GNSS-R studies have been initiated using CORS network points; however, since traditional methods do not yield sufficiently efficient results, directional use of geodetic GNSS antennas has been explored as a solution. Nevertheless, since geodetic GNSS antennas are not primarily designed for GNSS-R applications, this solution is not permanent and remains costly for reflectometry applications. In subsequent studies, the use of low-cost receivers and antennas has become widespread. However, these receivers and antennas were not originally designed for GNSS-R applications either. Therefore, recent studies have increasingly focused on antennas specifically designed for this technique.

[0008] Antennas produced using 3D printers are generally cost-effective communication equipment. These antennas can be designed with geometries that allow them to perform similarly to known antenna types, ensuring comparable performance in terms of gain, reflection, and polarization. As a result, cost-effective designs can produce antennas with characteristics equivalent to those found in the literature. Numerous variations of such designs have emerged in recent years.

[0009] In the known state of the art, there is patent document US2002113745. However, upon examination, it describes a four-ridged horn antenna structure. The referenced system operates in the Ku-band and is proposed as an element of a parabolic reflector antenna array. This antenna is not designed for GNSS-R applications. Therefore, its purpose and usage differ from our invention. Within the patent application, an antenna with equal E- and H-planes is described, and the mentioned four-ridged antenna operates in circular polarization.

[0010] AIM OF THE INVENTION

[0011] The 3D antenna used in the GNSS-R measurement system subject to this invention has been designed to be both cost-effective and directional, making it suitable for the intended application and compatible with a low-cost receiver. In this regard, the antenna used in the proposed measurement system is advantageous compared to geodetic GNSS antennas due to its lower cost and directional nature, making it more suitable for GNSS-R applications.

[0012] The invention pertains to a dual-ridged horn antenna structure. The technical effect of the dual-ridged design is that the signals received from the E-plane and H- plane of the antenna differ. Since this antenna is linearly polarized, it predominantly captures the signal component of an incoming electromagnetic wave in a single direction. Therefore, the antenna subject to this invention has been designed for directional use, allowing it to collect signals reflected from the ground in a single dimension.

[0013] Another objective of our invention is to use the antenna as a signal receiver in GNSS-R applications and for obtaining SNR data at L1 and L2 frequencies. Since GNSS-R is a technique used to determine surface characteristics, identifying the dominant frequency in terms of SNR (Signal-to-Noise Ratio) is crucial. Determining the dominant frequency is made possible by the directional use of the antenna proposed in this invention.

[0014] The antenna structure subject to our invention is produced using a three- dimensional printer and coated with metal. It is not manufactured directly from a conductor or metal. This feature makes it a cost-effective system. The ease of design and production distinguishes the antenna technically from the mentioned antenna and the studies available in the literature.

[0015] LIST OF FIGURES

[0016] Figure 1a. Perspective view of the invention

[0017] Figure 1 b. Side view of the invention

[0018] Figure 1c. Top view of the invention

[0019] Figure 1d. Front view of the invention

[0020] Figure 1e. Cross-sectional view of the invention, showing the connector and live end connection

[0021] Figure 2a. Return loss of the antenna

[0022] Figure 2b. Radiation pattern of the antenna in L1 band (polar graph)

[0023] Figure 2c. Radiation pattern of the antenna in L2 band (polar graph)

[0024] Corresponding references in the figures:

[0025] 1. Base

[0026] 2. Lower section

[0027] 3. Horn

[0028] 4. Side wall

[0029] 5. Bridge

[0030] 6. Ridge

[0031] 7. Connector

[0032] 8. Live end

[0033] DETAILED DESCRIPTION OF THE INVENTION

[0034] The invention is a low-cost GNSS reflectometry measurement system featuring a dual-ridged horn antenna produced by a 3D printer and coated with metal foil. It comprises a base (1 ), a horn (3), a lower section (2) connecting the base (1 ) to the horn (3), two closed side walls (4) on the horn (3), three bridges (5) connecting the closed side walls (4) on each side, and two ridges (6) extending from the base (1 ) to the top of the closed side walls (4), narrowing in width as they ascend.

[0035] A connector (7) is placed at the bottom of the antenna to receive GNSS-R signals. This connector (7) consists of an inner metal conductor, the live end (8), and an outer metal conductor (Figure 1e shows the cross-section of the antenna), which serves as the ground end (non-live end). The ground end contacts the lower section (2), while the live end (8) passes through the ridges and contacts the other ridge, allowing signal collection via the connector (7).

[0036] All parts, except for the bridge (5) and connector (7), are covered with metal foil. The bridge (5) consists of metal wires. Instead of fully enclosing the side surfaces with side walls (4), three evenly spaced rows of wire strips are used to create a more uniform radiation distribution. The gap between the ridges is g=4 mm (Figure 1d).

[0037] To summarize the invention: the technical design of the antenna was determined by experimentally calculating the antenna aperture (half-power beamwidth), and the dimensions were selected based on optimal values for directional gain and reflection threshold at L1 and L2 frequencies. The most suitable aperture antenna was produced using a 3D printer with plastic (PLA / Polylactic Acid) material. The antenna was then completely covered with a metal foil. The resulting antenna showed no performance disadvantages compared to a fully metallic antenna. As a result, a directional and cost- effective antenna was developed for GNSS-R applications aimed at determining surface characteristics. Additionally, a low-cost receiver was integrated with the antenna to establish a GNSS-R measurement system.

[0038] The dual-ridged horn antenna (Double Ridged Horn Antenna / DRHA) was manufactured using FDM-style additive manufacturing techniques. The internal ridge structures of the antenna are W3=5 mm wide. As seen in Figures 1 b and 1 d, the maximum ridge height is H3=55 mm. The outer surface of the printed antenna is entirely covered with 0.01 mm thick metal foil. Household aluminum foil and an adhesive were used for this coating.

[0039] The internal dimensions of the antenna’s bottom section are W1 =130 mm and H1 =100 mm. The structure rises vertically for L1 =50 mm from the base and then expands into a linear horn shape, with an extension length of L2=160 mm. The largest cross-sectional width of the horn section is W2=186 mm, and its height is H2=152 mm. Additionally, a 3 mm thick rear cover with dimensions H1 x W1 is included at the base (1 ) to close the bottom of the antenna. Figures 1a-1d present different views of the invention, while Figure 1e illustrates the cross-sectional view showing the connector and live-end connection.

[0040] The designed 3D-printed antenna operates at the global positioning frequencies of L1 and L2. An antenna is considered functional at a given frequency if its return loss falls below -10 dB. As shown in Figure 2a, the return loss of the antenna is below -10 dB at L1 =1575.42 MHz with a 10 MHz bandwidth and at L2=1227.6 MHz with an 11 MHz bandwidth, confirming that the antenna functions in these bands.

[0041] GNSS applications operate at very low power levels, requiring antennas that can receive signals over a broad range of arrival angles. To evaluate radiation patterns, the "First Null Beam Width" (FNBW), an antenna parameter representing the signal reception capability based on direction, was considered. For both L1 and L2 bands, the FNBW angles of the invention are approximately 145°. The maximum gain of the 3D-printed antenna is 9 dB for the L1 band and 8 dB for the L2 band. The antenna operates with linear polarization. Figures 2b and 2c illustrate the radiation patterns for the L1 and L2 bands, respectively.

Claims

CLAIMS1 . A low-cost GNSS reflectometry measurement system with a dual-ridged horn antenna, characterized by comprising a base (1), a horn (3), a lower section (2) connecting the base (1) to the horn (3), two closed side walls (4), three bridges (5) on each side, two ridges (6), a connector (7), and all parts except the bridges (5) and connector (7) being covered with metal foil.

2. The system of claim 1 , wherein the number of ridges (6) is two.

3. The system of claim 1 , wherein the antenna is produced using a 3D printer.

4. The system of claim 1 , wherein the connector (7) includes a live end (8) and a ground end.

5. The system of claim 4, wherein the ground end contacts the lower section (2).

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