Choke Ring Research Articles

Analysis of a Low-Earth Orbit Satellite Downlink Considering Antenna Radiation Patterns and Space Environment in Interference Situations

This paper investigates a low-Earth orbit (LEO) satellite downlink for high-speed data communication in interference situations. A choke ring horn type antenna is used as the data transmitting antenna with an isoflux pattern in the LEO satellite, which has a beam coverage of ±51.6° and a bore-sight gain of 4.4 dBi at 8 GHz. The receiving antenna on the ground station is a parabolic type antenna with a diameter of 11.3 m, and it has a half-power beam width (HPBW) of 0.2° with a maximum gain of 59 dBi at 8 GHz. The jamming-to-signal ratio (J/S) is calculated assuming that the LEO satellite transmits signals to the ground station, and an elevation angle of the interference source varies from 0° to 90° at an altitude of 10 km. Applying antenna characteristics, such as HPBWs and side lobes, to the calculated space wave path loss makes it possible to predict the J/S results according to the location of the interference source and the satellite. The results show that it is necessary to consider the space environment to accurately analyze the LEO satellite downlink, especially at the low elevation angle of the satellite.

Research on the Positioning Performance of GNSS with a Low-Cost Choke Ring Antenna

One of the technologies used for localization is GNSS (Global Navigation Satellite Systems), which is exposed to many phenomena, i.e., the occurrence of terrain covers, reflections of the radio waves, and the multipath nature of the radio waves in the propagation environment. To increase the resistance to environmental phenomena, special types of antennas are used, which include, among others, choke ring antennas. The article describes the design and construction of the choke ring antenna and the impact of the mentioned device on the quality of GNSS positioning. The accuracy of the constructed antenna (based on selected accuracy measures: DRMS, 2DRMS, SEP, MRSE, SAE) is calculated together with positioning errors determined for two types of antennas: choke ring antenna and the dedicated antenna supplied by the manufacturer in RTK mode. The results confirm that the designed choke ring antenna can be used for positioning without significantly losing accuracy in the RTK mode.

Compact Hybrid Choke Rings for Dual-Band Circularly Polarized GPS Antenna

This letter presents the compact hybrid choke rings for the dual-band circularly polarized global positioning system (GPS) antenna, in order to suppress the surface wave propagation and reduce the back lobe levels. The designed dual-band circularly polarized antenna is center-fed and composed of two radiation patches. The novel compact hybrid choke rings are introduced to reduce the radiation back lobes and improve the front to back ratio effectively. The measured results show that the return loss of the antenna is greater than 10 dB and the bandwidth covers GPS L2 from 1.168 to 1.238 GHz and GPS L1 from 1.543 to 1.599 GHz. In the working bands, the front to back ratio of the proposed antenna is greater than 30 dB.

Design and Installed Performance Analysis of a Miniaturized All-GNSS Bands Antenna Array for Robust Navigation on UAV Platforms.

Global navigation satellite systems (GNSS) are vital technologies of our age and serve a plethora of industries that rely on precise positioning for automation, efficiency, and safety. Emerging applications of unmanned aerial vehicles (UAV) in critical applications like security, surveillance, critical logistics and defense demand precise and robust navigation capabilities even in challenging environments with high multipath or (un-)intended interference. The design of robust GNSS receivers for UAV applications, capable of suppressing interfering signals, is challenging due to the need for multi-antenna systems and the stringent requirements on hardware to be lightweight and miniaturized enough to fit onto small mobile platforms. In order to overcome these limitations, the present article details a four-element wideband antenna array, fitting into a 100 mm diameter footprint. The array is capable to operate across all GNSS frequency bands while incorporating, if needed, a multipath mitigation solution. The antenna design relies on a modular concept with 3D printed Dielectric Resonator Antennas (DRAs) and vertical choke rings. The antenna performance is evaluated in terms of its radiation pattern via installed antenna simulations and measurements in an anechoic chamber. The effect of different installation heights on the antenna pattern is studied. Furthermore, GNSS measurements carried out with the array alone and mounted on the UAV are presented.

New Choke Ring Design for Eliminating Multipath Effects in the GNSS System

An anti-multipath antenna is an antenna that can effectively suppress multipath signals from the source of signal reception. There are many problems in the traditional choke design, such as excessive volume and low elevation gain damage. In this paper, the conventional choke ring is improved by using the complementary trapezoidal structure, and the detailed design process is given. The measured results show that the choke has good resistance to a multipath effect in the navigation frequency band (1.1–1.7 GHz) and can significantly improve the front-to-back ratio of the antenna.

A new acid gas destruction kinetic model for reaction furnace of an industrial sulfur recovery unit: A CFD study

• Developing a reduced reaction mechanism for acid gas combustion. • Simulating detailed full-scale reaction furnace with new reduced kinetic model. • Predicting accurate results in terms of temperature profile and chemical species. • Vectorwall and co-directional diffuser showed the lowest radiative heat flux. • Common checkerwall and co-directional diffuser showed the highest H2S efficiency. A new reduced kinetic model is developed for the simulation of acid gas destruction in the industrial reaction furnace of sulfur recovery units. The proposed CFD model includes the reactions of the new kinetic mechanism, steady laminar flamelet model, and fine details of industrial furnace geometry related to the burner, choke ring, checkerwall, and exhaust pipe holder. The mean relative error in predicting H 2 S conversion using CFD, coupled with our new kinetic model, is about 9.48% when compared with the industrial data. The influences of two types of burners and the checkerwalls on the thermohydrodynamics behaviors of the reaction furnace are investigated. The reactor equipped with Vectorwall and co-directional diffuser shows the lowest radiative heat flux (RHF) and favorable outlet temperature to protect the tube sheets, while the one with conventional checkerwall and co-directional diffuser shows the highest H 2 S conversion efficiency in the furnace.

A Dual-Polarized Horn Antenna Covering Full Ka-Band Using Turnstile OMT

This article presents a dual-polarized corrugated horn antenna incorporated a turnstile orthomode transducer (OMT) covering the full Ka-band (26.5–40 GHz). A three-stepped cylindrical tuning stub scattering element is designed in the turnstile junction to combine/split the two linearly polarized waves with high isolation. The proposed turnstile OMT shows a good simulated return loss better than 20 dB and a high isolation higher than 57 dB within the whole Ka-band. Then, a corrugated horn antenna with five-stage choke rings is designed. Finally, the proposed horn antenna incorporated in the turnstile OMT is fabricated and measured. The measured impedance bandwidth for |S11/22|≤ −15 dB is 50.7% from 25 to 42 GHz. The measured peak gain is 11.9 dBi. The proposed antenna system is a promising candidate for the 5G millimeter-wave applications.

Low-Profile Substrate Integrated Choke Rings for GNSS Multipath Mitigation

In this article, a novel technique for the miniaturization of corrugated structures is presented, and multifolded corrugations (MFCs) are introduced. The miniaturization is achieved by implementing multiple folds or slits inside corrugations. The proposed miniaturization technique is modeled using the modal expansion method. An equivalent circuit is extracted, which precisely models the surface impedance of the proposed MFCs. A time-efficient design procedure is presented based on the equivalent circuit model, and a dual-band double-folded substrate integrated choke ring (DFSICR) structure is designed to suppress the propagation of surface waves over the main global navigation satellite system (GNSS) frequency bands: L1 (1573–1587 MHz) and L2 (1215–1240 MHz). The DFSICR demonstrates significant multipath mitigation capabilities, close to that of a classic choke ring, while it eliminates the drawbacks of a conventional choke ring, such as large size, heaviness, costly fabrication, and inability to integrate with printed circuit board (PCB) structures. An example design shows miniaturization of 85% in height and 38% in diameter compared to the conventional choke ring. A prototype is fabricated using FR4 laminates, which demonstrates a weight reduction of more than 90% compared to the classic choke ring. The measurement results confirm the validity of the proposed technique.

Testing Patch, Helix and Vertical Dipole GPS Antennas with without Choke Ring Frame

Abstract: The antenna is the connecting part between Global Positioning System (GPS) satellite and receiver, and it works on transferring the satellite signal propagation to the receiver with minimum interruption. This is beside the main role that GPS antenna can play for accurate and precise positioning. High quality GPS antennas have high gain, systematic radiation pattern, Right Hand Circular Polarization (RHCP), and low directivity. Multipath error is a principal error source connected with GPS positioning and it can be mitigated using better antenna design. GPS antennas tend to be provided with choke ring frame for protection from the reflected RHCP electromagnetic waves. In this paper, the performance of three different types of GPS antenna, namely: Microstrip Patch Antenna (MPA), Helix antenna (HA), and Vertical Dipole antenna (VDA), with and without choke ring frame, has been investigated using single frequency GPS receiver. The antennas have been examined under the same GPS environment, including satellites constellation, geometry, and surroundings, with different heights from the ground reflector surface for multipath evaluation. Short base-line kinematic differential code GPS (DGPS) technique has been used for removing and mitigating the main GPS error sources and focusing on multipath effect. Satellite residuals and the quality of the obtained positioning have been considered for evaluating the performance of each antenna. The results have reflected the ability of choke ring frames to improve the performance of the three GPS antennas with different rates in multipath areas, and illustrate the advantages and limitations of each antenna. Keywords: Micro-strip, Patch, Helix, Vertical Dipole, GPS, Choke Ring Antenna, Multipath.

A High Gain Ku Band Antenna with Circular Polarization Using Hybrid Choke Ring Structure

A Novel Hybrid Choke High Gain Antenna (HCHGA) that operates at 15 GHz is presented in this article, HCHGA is a circularly polarized one that effectively mitigates the multipath effects. The proposed antenna has good impedance matching with S11 of −20.99 dB with a gain of 10.26 dB, and an axial ratio of 1.74 dB. The radiation patterns of the antenna are orthogonal to the antenna surface without any nulls. The proposed antenna is fabricated using RT Duroid 5880 substrate. Simulations are done on a basic patch antenna mounted on different types of ground planes including extended flat ground plane, concentric choke ring, and Hybrid choke ring. The effects of variation in the parameters of grooves thickness, grooves height, and grooves shape on antenna performance parameters are observed. The design of the hybrid chokes facilitated higher values of gain and front-to-back ratio development for mitigating the multipath. From the prototype of the proposed antenna, the measured and simulated results are in good agreement with each other and this proposed antenna is suitable for satellite communication applications.

Investigating GNSS multipath effects induced by co-located Radar Corner Reflectors

Abstract Radar Corner Reflectors (CR) are increasingly used as reference targets for land surface deformation measurements with the Interferometric Synthetic Aperture Radar (InSAR) technique. When co-located with ground-based Global Navigation Satellite Systems (GNSS) infrastructure, InSAR observations at CR can be used to integrate relative measurements of surface deformation into absolute reference frames defined by GNSS. However, CR are also a potential source of GNSS multipath effects and may therefore have a detrimental effect on the GNSS observations. In this study, we compare daily GNSS coordinate time series and 30-second signal-to-noise ratio (SNR) observations for periods before and after CR deployment at a GNSS site. We find that neither the site coordinates nor the SNR values are significantly affected by the CR deployment, with average changes being within 0.1 mm for site coordinates and within 1 % for SNR values. Furthermore, we generate empirical site models by spatially stacking GNSS observation residuals to visualise and compare the spatial pattern in the surroundings of GNSS sites. The resulting stacking maps indicate oscillating patterns at elevation angles above 60 degrees which can be attributed to the CR deployed at the analysed sites. The effect depends on the GNSS antenna used at a site with the magnitude of multipath patterns being around three times smaller for a high-quality choke ring antenna compared to a ground plane antenna without choke rings. In general, the CR-induced multipath is small compared to multipath effects at other GNSS sites located in a different environment (e. g. mounted on a building).

Choke ring horn antenna design for satellite payload data transmitters

AbstractIn low earth orbiting satellite communication systems, antennas are key elements for radio frequency transmitters and receivers. There are different types of antennas used on satellite communication systems. One of them is the antenna used in payload data transfer communication subsystem. Payload data transmitters for space segment should utilize the radio frequency power efficiently due to the limited power budget of the spacecraft. For low elevation angles of a low earth orbiting satellite, the free space loss increases as expected and it should be compensated. One way of this compensation is to employ an antenna having isoflux pattern. Therefore, in this paper, a circularly polarized X‐Band choked ring horn antenna is designed, optimized and manufactured due to its isoflux radiation characteristic and medium power handling capability. Initially, an analytical approach from the literature is explained and then the physical dimensions of the proposed antenna are optimized, iteratively, employing a commercially available electromagnetic solver. Next, a prototype has been manufactured to verify the radiation, return loss and port isolation characteristics and they are presented in the related section. Moreover, the results of the presented antenna have been compared to the ones available in the literature. These comparisons show that gain of the designed antenna at ±64° elevation angle has higher gain with respect to the compared ones. In addition, its axial ratio value is smaller than 6.5 dB for different azimuth angles between 8025 and 8400 MHz. Unlike the other studies given in the literature that have gain higher than 2 dB at ±64° elevation angle, in this study all design parameters have been presented to utilize through the operating bandwidth.

A Design of Hign Gain Wideband Circular Polarization Antenna Based on All-Metal Vivaldi Antenna

This paper designs a broadband circularly polarized antenna covering the 25 GHz to 31 GHz band. The Vivaldi antenna is used as the basic structure to generate broadband electromagnetic waves; circular polarization is achieved by feeding through a circularly polarized bridge; a metal choke ring is used at the bottom to ensure the low side lobes of the antenna. The antenna consists of four basic Vivaldi antennas, a metal choke ring, a grounded substrate, and a feed network. The results show that the antenna covers the entire frequency band when the axial ratio is lower than 3 dB, and the impedance matching is better. The use of a choke ring structure ensures that the antenna electromagnetic waves are radiated upward, resulting in higher gain and lower side lobes. The highest gain in the included frequency band is 11.4 dB, and the simulation result is good. The antenna has high gain and low sidelobe characteristics.

Absolute robotic GNSS antenna calibrations in open field environment

We consider robotic calibrations of GNSS receiving antennas in an open field environment. At the newly built test range, the sky is unobstructed down to 10° elevation; an industrial robot with six degrees of freedom is employed. The antenna calibration algorithm uses single differences of carrier phases. Two types of antennas are tested, a common choke ring ground plane antenna and a rover-type antenna. Three types of errors are analyzed in detail: far-field multipath, near-field multipath, and errors of antenna positioning by the robot. For far-field multipath, it has been shown that the notion of the satellite signal reflection by the plain surface underneath the antenna fits well with the observed data. Parallel vertical antenna displacements are analyzed to decrease the test time. It has been shown that the near-field multipath originating from the body of the robot is the main contribution to the remaining error of calibrations: while error components related to the remaining far-field multipath and inaccuracies in the geometry of the installation are estimated at 0.1 mm each, the overall accuracy of achieved calibrations is estimated as 0.3 mm for choke ring-type antenna and as 0.7 mm for rover-type antenna. A comparison of the obtained calibrations with Geo++® GmbH data is provided.

Reducing multipath effect of low-cost GNSS receivers for monitoring by considering temporal correlations

Abstract The investigations on low-cost single frequency GNSS receivers at the Institute of Engineering Geodesy (IIGS) show that u-blox GNSS receivers combined with low-cost antennas and self-constructed L1-optimized choke rings can reach an accuracy which almost meets the requirements of geodetic applications (see Zhang and Schwieger [25]). However, the quality (accuracy and reliability) of low-cost GNSS receiver data should still be improved, particularly in environments with obstructions. The multipath effects are a major error source for the short baselines. The ground plate or the choke ring ground plane can reduce the multipath signals from the horizontal reflector (e. g. ground). However, the shieldings cannot reduce the multipath signals from the vertical reflectors (e. g. walls). Because multipath effects are spatially and temporally correlated, an algorithm is developed for reducing the multipath effect by considering the spatial correlations of the adjoined stations (see Zhang and Schwieger [24]). In this paper, an algorithm based on the temporal correlations will be introduced. The developed algorithm is based on the periodic behavior of the estimated coordinates and not on carrier phase raw data, which is easy to use. Because, for the users, coordinates are more accessible than the raw data. The multipath effect can cause periodic oscillations but the periods change over time. Besides this, the multipath effect’s influence on the coordinates is a mixture of different multipath signals from different satellites and different reflectors. These two properties will be used to reduce the multipath effect. The algorithm runs in two steps and iteratively. Test measurements were carried out in a multipath intensive environment; the accuracies of the measurements are improved by about 50 % and the results can be delivered in near-real-time (in ca. 30 minutes), therefore the algorithm is suitable for structural health monitoring applications.

Performance Comparison of KOMPSAT-5 Precision Orbit Determination with GRACE

The Korean Multipurpose Satellite-5 (KOMPSAT-5) launched on 22 August 2013 was equipped with a global positioning system (GPS) receiver for precision orbit determination (POD). Even though the GPS receiver of KOMPSAT-5 shares the same heritage as the BlackJack receiver onboard in Gravity Recovery and Climate Experiment (GRACE) satellites, KOMPSAT-5 has a lower orbital position accuracy (~10 cm) compared with GRACE (~2 cm). The reduced dynamic and kinematic methods are applied for POD of KOMPSAT-5 and GRACE to investigate the GPS observation quality due to the satellite operation concept and hardware design. The results are analyzed in terms of the number of observations and their spatial distribution, GPS signal quality, and orbital position accuracies. The results show that the frequent attitude maneuvers of KOMPSAT-5 affect the quality of the GPS signals and solutions obtained from the kinematic method compared with that determined from the reduced-dynamic method. The onboard patch GPS antenna installed in KOMPSAT-5 and its geometrical position resulted in more erratic measurement residuals by 140% compared with the choke ring antenna of GRACE. The POD accuracy is dependent on the hardware design and regular attitude tilting for the synthetic aperture radar (SAR) imaging even though the same GPS receiver performances.

NOx emission from a sulfur recovery unit thermal reactor with rounded corners or a vector wall

A sulfur recovery unit (SRU) thermal reactor is important equipment in a sulfur plant. Because its operating temperature is very high, the nitrogen oxides (NOx) produced by a SRU thermal reactor is one of the possible sources of air pollution. In this paper, NOx emission from a practical SRU thermal reactor is analyzed. Both the prototype thermal reactor and its modifications, including modifying the reactor geometry and using a vector wall are compared. Simulation results show that the SRU thermal reactor with a radius of curvature 1m at the zone 1 corner has the lowest NO emission. Compared with using a choke ring, the NO concentration at the reactor exit is higher using a vector wall.

CASSIOPE orbit and attitude determination using commercial off-the-shelf GPS receivers

As part of the “GPS Attitude, Positioning, and Profiling experiment (GAP)” of the Canadian CASSIOPE science and technology mission, a set of four geodetic GPS receivers connected to independent antennas on the top-panel of the spacecraft can be operated concurrently to collect dual-frequency code and phase measurements on both the L1 and L2 frequencies. The qualification of the commercial off-the-shelf (COTS) GPS receivers is discussed, and flight results of precise orbit and attitude determination are presented. Pseudorange and carrier phase errors amount to roughly 65 cm and 8 mm for the ionosphere-free dual-frequency combination, which compares favorably with other missions using fully qualified space GPS receivers and is mainly limited by choice of simple patch antennas without choke rings. Precise orbit determination of CASSIOPE using GPS observations can achieve decimeter-level accuracy during continued operations but suffers from onboard and mission restrictions that limit the typical data availability to less than 50% of each day and induce regular long-duration gaps of 4–10 h. Based on overlap analyses, daily peak orbit determination errors can, however, be confined to 1 m 3D on 84% of all days, which fulfills the mission needs for science data processing of other instruments. The attitude of CASSIOPE can be determined with a representative precision of about 0.2° in the individual axes using three GAP receivers and antennas. Availability of dual-frequency measurements is particularly beneficial and enables single-epoch ambiguity fixing in about 97% of all epochs. Overall, the GAP experiment demonstrates the feasibility of using COTS-based global navigation satellite system receivers in space and the benefits they can bring for small-scale science missions.

Metallic Monopole Parasitic Antenna With Circularly Polarized Conical Patterns

In this paper, a new geometry for antenna producing conical patterns with circular polarization is proposed. The symmetrically placed parasitic posts, with different horizontal and vertical segments, around the centrally fed monopole control the circular polarization purity and the angle of maximum gain. The 3-D geometry favors high gain at low elevation angles. A circular ground plane atop a choke ring facilitates easy mounting of a radome and improves gain at lower elevation due to lower backlobe. The all-metal radiator has good mechanical stability and remains impervious to large temperature variations, which is ideal for use in space applications. An application to a Martian transponder at the $X$ -band is also discussed. The measured results of the manufactured antennas show a good agreement with those of the simulated one. Furthermore, the optimization of the antenna design parameters allows the antenna to have high gain and low axial ratio (AR), from high elevation ( $\theta _{max}=35^{\circ }$ ) to low elevation ( $\theta _{max}=70^{\circ }$ ) angles.

Surface Impedance Engineered Low-Profile Dual-Band Grooved-Dielectric Choke Ring for GNSS Applications

A novel low-profile grooved-dielectric choke ring with dual-band surface impedance resonance is proposed and experimentally demonstrated. The proposed structure is designed by engineering the surface impedance of a dielectric-based choke ring to introduce two resonant frequencies around the global navigation satellite system (GNSS) bands of L2 (1227.60 MHz) and L1 (1575.42 MHz). This provides capacitive surface impedances around both bands simultaneously, which is required for efficient surface wave suppression for higher multipath rejection performance. To demonstrate the proposed principle of surface impedance engineering, an in-house choke ring prototype of the proposed design is tested with the widely used Dorne and Margolin antenna. A high multipath rejection in both GNSS bands is experimentally confirmed with comparable performances to an otherwise bulky, heavy, and expensive conventional metallic choke ring.