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Multiband circularly-polarized stacked elliptical patch antenna with eye-shaped slot for GNSS applications
Abstract
This paper introduces a tri-band stacked elliptical patch antenna featuring a right-handed circular polarized, designed to operate at the L2, L5, and L1 Global Navigation Satellite System bands. Initially, an elliptic patch is constructed and fed by a probe feed to generate TM 110 and TM 210 modes at resonance frequencies calculated using Mathieu functions. The probe position is precisely adjusted to excite the quasi-orthogonal mode of TM 110 to generate circularly polarized (CP) waves at the L2 and L5 bands. Subsequently, an eye-shaped aperture is engraved into the elliptical patch to enhance the axial ratio (AR) beamwidth in the L2 and L5 bands and stimulate the orthogonal mode of TM 210 to produce CP waves at the L1 band. Lastly, a stacked partially elliptical parasitic element is placed beneath the upper slotted elliptical patch to enhance the orthogonality of TM 210 surface current versions and thus improve the AR beamwidth at the L1 band. The proposed antenna shows low reflection coefficient values at 1.12–1.33 (L2/L5), and 1.5–1.66 GHz (L1). The AR beamwidths are 133/213 ∘ , 167/163 ∘ , and 36/103 ∘ at two orthogonal cutplanes at L5, L2, and L1 bands, respectively. The antenna also has decent gains of 6–6.9 dBic across the three bands.
... Traffic moving object detection in real-world recorded videos is used to recognize the changing or moving areas in the camera view [1][2][3]. It is an essential task in computer vision and plays a vital role in various applications, including intelligent transportation systems (ITSs), fault detection, area monitoring, motion capture, disaster management, scene analysis, and visual surveillance [4][5][6][7][8]. Several image processing algorithms have been developed, in the literature, to detect a particular object or event in the video scenes. ...
Moving object detection is a vital research area that plays an essential role in intelligent transportation systems (ITSs) and various applications in computer vision. Recently, researchers have utilized convolutional neural networks (CNNs) to develop new techniques in object detection and recognition. However, with the increasing number of machine learning strategies used for object detection, there has been a growing need for large datasets with accurate ground truth used for the training, usually demanding their manual labeling. Moreover, most of these deep strategies are supervised and only applicable for specific scenes with large computational resources needed. Alternatively, other object detection techniques such as classical background subtraction need low computational resources and can be used with general scenes. In this paper, we propose a new a reliable semi-automatic method that combines a modified version of the detection-based CNN You Only Look Once V4 (YOLOv4) technique and background subtraction technique to perform an unsupervised object detection for surveillance videos. In this proposed strategy, background subtraction-based low-rank decomposition is applied firstly to extract the moving objects. Then, a clustering method is adopted to refine the background subtraction (BS) result. Finally, the refined results are used to fine-tune the modified YOLO v4 before using it in the detection and classification of objects. The main contribution of this work is a new detection framework that overcomes manual labeling and creates an automatic labeler that can replace manual labeling using motion information to supply labeled training data (background and foreground) directly from the detection video. Extensive experiments using real-world object monitoring benchmarks indicate that the suggested framework obtains a considerable increase in mAP compared to state-of-the-art results on both the CDnet 2014 and UA-DETRAC datasets.
Global Navigation Satellite System—Reflectometry (GNSS-R) has already proven its potential for retrieving a number of geophysical parameters, including soil moisture. However, single-pass GNSS-R soil moisture retrieval is still a challenge. This study presents a comparison of two different data sets acquired with the Microwave Interferometer Reflectometer (MIR), an airborne-based dual-band (L1/E1 and L5/E5a), multiconstellation (GPS and Galileo) GNSS-R instrument with two 19-element antenna arrays with four electronically steered beams each. The instrument was flown twice over the OzNet soil moisture monitoring network in southern New South Wales (Australia): the first flight was performed after a long period without rain, and the second one just after a rain event. In this work, the impact of surface roughness and vegetation attenuation in the reflectivity of the GNSS-R signal is assessed at both L1 and L5 bands. The work analyzes the reflectivity at different integration times, and finally, an artificial neural network is used to retrieve soil moisture from the reflectivity values. The algorithm is trained and compared to a 20-m resolution downscaled soil moisture estimate derived from SMOS soil moisture, Sentinel-2 normalized difference vegetation index (NDVI) data, and ECMWF Land Surface Temperature.
In the paper, a low-profile dual-band printed quadrifilar helix antenna (PQHA) with wide beamwidth is presented for UAV GPS applications. The antenna is composed of a hollow dielectric cylinder with four arms of dual-helix metal strips and a hollow dielectric ring with four pairs of circular metal strips. To provide dual-band operation, different lengths of the dual-helix metal strips are applied. By loading the circular metal strips on the dual-helix metal strips, size reduction of the antenna height is realized. Moreover, wide beamwidth is obtained. A miniaturized quad-feed network is also designed to provide equal amplitude signals with sequentially quadrature phases. To validate the proposed structure, a prototype is fabricated. The height of the antenna is 18.5 mm. The experimental results show that good impedance matching (|S11| < -18 dB) and axial ratio (< 2 dB) are obtained at GPS L1/ L2 bands. At 1.227 GHz, the measured 3-dB axial ratio beamwidths (ARBWs) are 186° and 187° at xoz and yoz planes, respectively. While the values are 167° and 163° at 1.575 GHz. The measured half-power beamwidths (HPBWs) are both more than 120° at the two bands. The results indicate that the proposed PQHA is a good candidate for UAV GPS applications.
Wireless transmission based on orbital angular momentum (OAM) can improve spectrum utilization, but it requires effective OAM mode generation. Using the characteristic mode analysis, it is easy to obtain degenerate mode distributions of the symmetric rectangular patch. The coupling phase difference of 90° between two degenerate modes can be implemented by disrupting the symmetry. In that case, a single feed structure located at the common position of equal mode current amplitudes can excite two degenerate modes to synthesize OAM modes. When the fundamental degenerate modes of the rectangular patch antenna are used, only the field component along the beam direction has the characteristics of the first order OAM. To achieve higher order OAM modes, the patch structure should be further adjusted. By introducing slots in the patch edges and grounding the patch at its center, the single‐fed rectangular patch antenna can radiate the vortex wave carrying the second order OAM. Furthermore, the OAM mode performance such as mode purity can be analyzed by the modal excitation coefficients.
This paper presents a dual-band circularly polarized cross-dipole antenna with wide axial ratio (AR) beamwidth for full upper hemispherical coverage for GPS L1 and L2 bands. The antenna has curved radiating arms and a corrugated back cavity to enhance the beamwidth. A wideband hybrid coupler is used to feed the antenna at the two nearby frequency bands. Experimental results show that very wide 3-dB AR beamwidths of over 200° can be obtained, fully covering the upper hemisphere for the two GPS bands.
A broadbeam cross-dipole antenna with improved low-elevation gain for Global Positioning System (GPS) applications is reported. The cross dipole consists of two perpendicular dipoles, which are printed on two separate substrates that are vertically placed inside a cylindrical back cavity. Circularly polarized fields are generated by applying two quadrature signals with equal amplitude to the dipoles. To enhance the low-elevation gain, circular dipoles, curved ground planes, and corrugated back cavity are deployed in our design. A prototype operating in GPS L1 band (1.575 GHz) was designed with ANSYS HFSS, and measurement was done to verify the simulations. The reflection coefficient, axial ratio (AR), radiation pattern, antenna gain, and antenna efficiency are studied. It is found that the antenna has a wide 3-dB AR beamwidth of over 230° and a 3-dB gain beamwidth of 150°. The measured and simulated antenna gains at θ = 85° are 0.11 dBic and 0.68 dBic, respectively, which are higher than those of existing designs.
The Global Positioning System (GPS) signals are used for navigation and positioning purposes by a diverse set of users. As a part of GPS modernization effort L5 has been recently introduced for better accuracy and availability service. This paper intends to study and simulate the GPS L1/L5 signal in order to fulfill the following two objectives. The first aim is to point out some important features/differences between current L1 (whose characteristics have been fairly known and documented) and new L5 GPS signal for performance evaluation purpose. The second aim is to facilitate receiver development, which will be designed and assembled later for the actual acquisition of GPS data. Simulation has been carried out for evaluation of correlation properties and link budgeting for both L1 and L5 signals. The necessary programming is performed in Matlab.
A new and circularly polarized (CP) antenna is
proposed for global navigation satellite systems (GNSS)
applications. The antenna employs a single feed and two
orthogonally elliptical printed dipoles. The dipoles are crossed
through a 90° phase delay line of a vacant-quarter printed ring
to achieve CP radiation. In order to achieve broad beamwidth,
four metallic cylinders are introduced. The proposed antenna
has achieved a bandwidth of about 43% from 1.08 to 1.69 GHz
for S11 < -10 dB. Meanwhile, the CP bandwidth is from 1.55 to
1.63 GHz (L1) and 1.12 to 1.26 GHz (L2, L5) for axial ratio < 3
dB. Additionally, the antenna yields right-hand circular
polarization (RHCP) and high antenna efficiency over a wide
frequency band. The simulated results have shown that the
proposed antenna is a good candidate for GNSS applications.
In this study, a compact, triple-band, circularly polarised stacked microstrip antenna is proposed over the artificial metasurface called reactive impedance surface (RIS) for enhancing antenna radiation efficiency for GPS applications. The proposed design utilises the concept of combining multi-stacked patches with RIS as imaginary-impedance metamaterial-ground-plane for selective frequency reduction of lower bands with improvement in antenna radiation properties for multi-band applications. The circularly polarised (CP) radiation with compact antenna size is achieved for triple-band GPS frequencies of L1 (1.575 GHz), L2 (1.227 GHz) and L5 (1.176 GHz) by placing three stacked patches with two different pairs of symmetric slits, four different sized symmetric cross-shaped slots and truncated corners over RIS. As RIS meta-surface reduces the wave penetration through the lossy substrate beneath it, the proposed stacked patch antenna over RIS demonstrates enhanced forward gain with suppressed back radiation. The measured results for antenna prototype are (1.168–1.185 GHz): L5 band, (1.2–1.245 GHz): L2 band and (1.51–1.59 GHz): L1 band for 10 dB return loss bandwidth with good CP radiation. Forward (boresight) right-handed CP gain of 2.88 dBic (L5 band), 3.25 dBic (L2 band) and 5.53 dBic (L1 band) is observed for compact antenna overall volume of 0.32/spl lambdao × 0.32λo × 0.024λo at 1.2 GHz.
A compact, dual band, circularly polarized (CP) multilayered stacked microstrip antenna over reactive impedance surface (RIS) is studied and presented in this paper. The CP radiation with compact antenna size is achieved by placing two asymmetric slit square patch (ASSP) and cross-shaped slotted square patch (CSSP) radiators over the RIS. Dual band is achieved by using the CSSP and ASSP stacked patches placed over RIS, fed by a coaxial probe at proper location to generate CP radiation. The measured results of the proposed antenna are 1.61% (1.235-1.255 GHz): L2 band and 1.25% (1.585-1.605 GHz): L1 band for 3-dB axial ratio bandwidth (BW), 2.00% (1.235-1.260 GHz): L2 band and 1.57% (1.580-1.605 GHz): L1 band for 10-dB impedance BW, and 2.68 dBic: L2 band and 4.46 dBic: L1 band for gain at the boresight for compact antenna overall volume of 0.26λo × 0.26λo × 0.018λo at 1.2 GHz.
The behavior of the Mathieu functions is illustrated by using a variety
of plots with representative examples taken from mechanics. We show how
Mathieu functions can be applied to describe standing, traveling, and
rotating waves in physical systems. Some background is provided on
notation and analogies with other mathematical functions. Our goal is to
increase the familiarity with Mathieu functions in the scientific and
academic community using visualization. For this purpose we adopt a
strategy based on visual recognition rather than only looking at
equations and formulas.
A new technique to achieve high front-to-back radiation ratios of slot antennas is presented. A 0.8 mm thin metasurface is loaded onto a circularly-polarised slot antenna and backed by a metallic reflector at close distances. The antenna has an overall height of ~ 0.1 wavelengths. However, it exhibits wideband characteristics with a measured impedance bandwidth (voltage standing-wave ratio ≤ 2) of 73.3% and a 3 dB axial-ratio bandwidth of 29.1%. A broadside gain of 7 dBic with a front-to-back ratio of 23.7 dB is achieved at 2.7 GHz.
A novel circularly polarized (CP) antenna with wide angular coverage is presented. The proposed antenna is formed by two bowtie patch antennas and two electric dipoles. It can achieve an impedance bandwidth (SWR < 1.6) of 41% and a 3-dB axial ratio bandwidth of 33%. For this design, very stable and symmetrical radiation patterns are obtained. In the axial ratio passband, the 3-dB beamwidth is 85<sup>deg</sup>plusmn2<sup>deg</sup> with a gain of 6.3 dBi plusmn0.3 dBi. The cross polarization is lower than -15 dB over a wide range of angles. For the entire half-power beamwidth, the axial ratio can be kept below 3 dB.
A dual-band single-feed circularly polarized, S-shaped slotted patch antenna with a small frequency-ratio is proposed for GPS applications. An S-shaped slot is cut at the centre of a square patch radiator for dual-band operation. A single microstrip feed-line is underneath the center of the coupling aperture ground-plane. The frequency-ratio of the antenna can be controlled by adjusting the S-shaped slot arm lengths. The measured 10-dB return loss bandwidths for the lower and upper-bands are 16% (1.103-1.297 GHz) and 12.5% (1.444-1.636 GHz), respectively. The measured 3-dB axial-ratio (AR) bandwidth is 6.9% (1.195-1.128 GHz) for the lower-band and 0.6% (1.568-1.577 GHz) for the upper-band. The measured gain is more than 5.0 dBic over both the bands. The measured frequency-ratio is 1.28. The overall antenna size is 0.46 ??<sub>o</sub> ?? 0.46??<sub>o</sub> ?? 0.086??<sub>o</sub> at 1.2 GHz.
This letter presents a unique compact cavity-backed tri-band antenna design for supporting simultaneous Global Navigation Satellite System (GNSS) (
L
1/
L
5) and Satellite Digital Audio Radio Service (SDARS) operations in a rooftop flush mount configuration. The cavity dimensions are 100 mm in diameter and only 9.35 mm in depth to meet a specific automobile manufacturer's physical dimension requirement. The achieved half-power realized gain bandwidths at L1, L5, and SDARS bands are 85, 54, and 250 MHz, respectively. This design consists of a bottom feeding board, a top GNSS board, and a middle SDARS board. All three boards are connected using vertical wires. The left-hand circular polarization (LHCP) SDARS element is a C-line coupled circular patch element that is excited via a novel traveling-wave proximity-coupling method that maximizes the passage of the out-of-band signals. The right-hand circular polarization (RHCP) dual-ring GNSS element is excited after the SDARS element using two orthogonal tapered-width proximity probes which are connected to two microstrip lines with different lengths for producing 90° phase difference at 1.4 GHz. The entire antenna assembly is connected to a single subminiature version A (SMA) connector. The design specifications and operating principles of the proposed antenna are discussed along with comparisons between the simulation and measurement performance obtained from a fabricated prototype.
A compact circularly-polarized patch antenna with wide axial-ratio beamwidth (ARBW) operating at dual bands compatible for GPS satellite navigation application is proposed in this paper. The antenna consists of two stacked patches, which account for GPS L1 band (1575 ± 2 MHz) and L2 band (1228 ± 2 MHz). To realize significant size miniaturization, four pillars are introduced and strongly coupled to the lower patch. To adjust the beamwidth response of the far-field components, the antenna is backed by a modified metallic cavity, which in turn widen the 3-dB axial ratio beamwidth (ARBW) at two operating bands effectively Finally, the proposed design with excellent performance is realized in a size of 0.368 λ0 (diameter) and 0.105 λ0 (height). Simulated and measured results show that the ARBWs at L1 and L2 bands are as wide as 173° and 133°, respectively. For practical application, its satisfactory GPS signal receiving capability is also verified by outdoor positioning test.
A conformal self-balanced asymmetric two arm GPS antenna is proposed in this paper. The proposed antenna is designed at GPS L1 frequency band of 1.575GHz. The antenna is designed on a windshield substrate and the two arms of the antenna are truncated asymmetrically to achieve circular polarization. The antenna is fabricated by sputtering and electroplating. Furthermore, full wave simulations and measurements are performed to justify that the proposed antenna operates efficiently when conformed to the windshield of an automobile. VSWR of 1.065 and an axial ratio of 1.81dB at 1.575GHz are obtained.
A novel aspect in cross-polarization (XP) reduction in probe-fed circular microstrip patch antenna has been proposed employing a pair of symmetric circular clusters of shorting pins (CCSP) peripherally located along the radius of the patch. The proof of concept is first established using a pair of shorting pins located symmetrically on the circular patch. Once the optimum position of the shorting pins for maximized XP reduction was identified, the design was modified by replacing an individual shorting pin using multiple numbers of shorting pins arranged in a circular geometry that is defined as CCSP. Effect of the incorporation of CCSP structures on the antenna characteristics like resonance frequency, co-polarized and cross-polarized radiation has been studied extensively. The design concept has been discussed and experimentally established using simulated and measured results of CCSP integrated circular patch over conventional circular patch for S-band. The integration of CCSP resulted in a relative suppression in XP levels of around 51 dB at the boresight and an average of 30 dB around ±60° on either side of boresight in both the principal radiation planes.
This paper presents a compact circularly polarized (CP) patch antenna with wide axial ratio (AR) beamwidth. The simulation reveals that by etching two pairs of asymmetric slots on the patch and loading coupled strips, the phase differences between the radiated orthogonal fields become flatter and maintain approximately at 90 degrees over a wide angular range, hence a wide AR beamwidth is achieved. Experimental results agree well with the simulation results. Particularly, this antenna achieves a wide AR beamwidth of 188 degrees in both the principle and diagonal planes.
A wide-beam circularly polarized (CP) cross-dipole antenna for GNSS applications is proposed in this article. This cross-dipole antenna is fed by a coaxial cable, on which the slots is added to optimize the impedance matching. These two pairs of dipole arms are designed with different lengths to obtain the circularly polarized radiation. Enhanced wide-beam CP radiation characteristics can be achieved by curving the dipole arms and adjusting the distance between the arms and the metallic ground plane. The study of proposed antenna performance with different geometric parameters has been conducted. The final antenna exhibits a good impedance bandwidth (IBW) of ∼13.1% (1.50-1.71 GHz), and the 3-dB axial-ratio bandwidth is over 7% (1.52-1.64 GHz). Broad pattern coverage of more than 140°, pure CP radiation at all designed bands and a wide 3 dB axial-ratio beamwidth (ARBW) of nearly 150° makes this antenna an excellent candidate for satellite communications and navigation systems.
Chapter 1. Global Navigation Satellite Systems.- Chapter 2. Doppler Satellite Positioning, Telemetry and Data Systems.- Chapter 3. Precision and Navigational PNT Systems.- Chapter 4. Aided and Augmentation Systems, and Differential GPS.- Chapter 5. Applications of PNT Systems.- Chapter 6. National and International Governmental Policy Issues.- Chapter 7. Conclusions and Future Directions.- 8. Top Ten Things to Know About GNSS.- Appendix 1. Key Terms and Acronyms.- Appendix 2. Selected Bibliography.- Appendix 3. Selected Websites.
Circles, ellipses, squares, rectangles, rhombuses and cross shapes are all special cases of Lamé curves (also known as superellipses). As a further generalization of Lamé curves, the Belgian botanist Johan Gielis introduced the notion of the so-called superformula with a view to the application to modeling and understanding the shapes of plants and animals. Despite the fact that Gielis’ superformula is expressed by a single simple equation, it can describe a wide range of various shapes, including, for example, triangle-like shapes, star-like shapes, flower-like shapes and so on. So far, it seems that most of the studies about Gielis curves (the curves generated by Gielis’ superformula) are application-oriented. In this paper, we examine precisely and analytically the mathematical structure of Gielis curves from a theoretical point of view. The original equation of the superformula has six parameters, which is too many to deal with at once. Therefore, we focus on a restricted case where the number of the parameters is reduced to three. In particular, we analyze the curvature at the “corners” and the midpoint of the “sides” of Gielis curves. We also derive the limit curves of Gielis curves and compare them with regular polygons.
Experiments with probe-fed circular patches using conventional and defected ground planes flashed some interesting features relating to cross-polarized (XP) electric fields and associated radiations before the present authors. Those led to a series of new investigations for understanding the nature of XP fields and to deal with them using defected ground structure (DGS) for improved XP performance. In the first phase of investigation, the XP radiations of a probe-fed circular patch with conventional ground plane have been critically studied as a function of the radial probe location. Remarkably significant effect is experimentally demonstrated. New information about orthogonal resonant fields and its importance in designing an antenna is provided. In the second phase of investigation, limitations of dot-shaped DGS in reducing XP level are experimentally studied. As its improved variants, two new DGS geometries such as annular ring and circular arcs have been explored. The arc-DGS appears to be highly efficient in terms of suppressing XP fields. Suppression by 10–12 dB has been experimentally demonstrated. Each design has been experimented in both C- and X-bands to earn confidence on the measured data.