Flat-topped Radiation Pattern Research Articles

A Compact Singly Fed Dielectric Resonator Antenna With Flat-Top Radiation Patterns

A Compact Singly Fed Dielectric Resonator Antenna With Flat-Top Radiation Patterns

Способ построения двухэлементной цифровой антенной решетки для оценки угловых координат радиосигналов со сверхразрешением с повышенной точностью на основе нижней границы Крамер-Рао

In the paper an effective method for optimal placement of directional antenna elements for digital spatial signal estimation is discussed. The digital antenna array evaluates spatial coordinates with the subsequent beamforming. However, as it is well known, the relative position of antenna elements, their number and the shape of the radiation pattern have a significant impact on the quality of the spatial pseudospectrum. The paper uses the previously obtained expression for estimating the Cramer-Rao lower bound to reduce the number of antenna elements without losing the accuracy of direction-of-arrival estimation of the signals. For example, a two-element array is obtained. The elements have a flat-top radiation pattern. It is shown that the accuracy of the MUSIC method in the obtained array is higher or comparable to the array composed of three elements.

Methods of synthesis of overlapped subarrays with flat-topped radiation patterns in planar phased array antennas

One of the approaches to the design of phased array antennas (PAA) for beam scanning in a limited region of space is associated with formation of overlapped subarrays with flat-topped radiation patterns of width equal to the width of the scan region. Unlike linear subarrays, for which there exist many technical solutions, planar overlapped subarrays can be formed by two ways. One of them is based on cascade connection of linear subarrays arranged perpendicularly to each other. Another way is based on use of beamforming networks. Since the problems concerning synthesis of overlapped subarrays with flat-topped patterns in planar PAA is not yet sufficiently considered in the literature, the indicated problem remains of interest. The work considers two methods of synthesis of planar overlapped subarrays with flat-topped radiation patterns. One method is a conventional method based on Fourier transform of the required radiation pattern. Another method introduced in the paper is new one. It allows determination of amplitude distribution over subarray aperture with providing maximum level of the subarray factor in the broadside direction and with taking into account power balance distributed over the subarray radiating elements. The proposed method is compared with the conventional method based on the Fourier transform, and advantages of the former method over the latter one are shown. The paper contains results obtained for amplitude distributions for a few cases of subarray excitation and appropriate subarray factors characterizing the capabilities of the new method. The method proposed in the paper can be applied in the further studies concerning development of networks for feeding overlapped subarrays in planar limited-scan PAA of modular construction.

Low-profile metasurface lens antenna with flat-top radiation pattern

This paper proposes a low-profile metasurface (MS) lens antenna with flat-top radiation pattern. Specifically, a low-profile slot array fed by the pillbox system serves as the feeding source while an MS lens placed close to the slot array can further shape the beam to flat-top radiation pattern. Compared with the conventional MS lens antennas with a single feeding source, the overall profile is greatly reduced and the fabrication stability is improved. Theoretical analyses, simulations, and measurements are carried out in this study. The proposed MS lens antenna operates at a central frequency of 28.5 GHz, aiming at supporting 5G millimeter-wave (mmW) communications. The measured results agree well with the analyzed and simulated ones. The proposed MS antenna realizes the flat-top pattern of over ± 20° with the measured peak gain of 10.5 dBi. The overall size is 78 mm × 63 mm × 4.4 mm, corresponding to 7.4λ0 × 6λ0 × 0.42λ0 at 28.5 GHz (λ0 is the free-space wavelength).

An Orthogonal Beamforming Network Synthesis Method Based on Complex Givens Rotation Matrix

This letter studies the possibility of synthesizing an orthogonal beamforming network (BFN) with an arbitrary number of inputs and outputs and beam-shaping functions. The proposed synthesis approach is based on complex Givens rotation matrices and is realized through the optimized program. First, it is derived that a complex Givens rotation matrix can represent a directional coupler with corresponding power ratio and phase difference. Then, this letter presents a computer-aided program to synthesize BFN that combines matrix cascading techniques and optimization algorithms, achieving beam shaping function. For validating the proposed synthesis approach, an example of an orthogonal 2×6 BFN with flat-topped radiation patterns for diversity application is presented. The accuracy and efficiency make the proposed synthesis method beneficial in antenna array systems.

Flat-Topped Radiation Pattern Synthesis of a Conformal Leaky-Wave Holographic Antenna

A novel method to synthesize a flat-topped pattern in single-curvature conformal leaky-wave antennas (CLWAs) is presented. When synthesizing the antenna, aperture field estimation (AFE), the holographic principle, the transformation optic (TO) approach, and the effects of the geometrical parameters of a curved structure on the far-field radiation pattern are considered. In the design process, three software packages (HFSS, MATLAB, and CST) are used to achieve the desired far-field radiation pattern at the design frequency. The shaped beam is in the broadside direction at 10 GHz. This CLWA is composed of unit cells with square patches that are printed on a double-layer grounded substrate which consists of PLA (Polylactic Acid) and Rogers RO4003 having thicknesses of 4 mm and 0.127 mm, respectively. An edge-fed 1:8 power divider excitation with a substrate integrated waveguide (SIW) structure is designed to illuminate the hologram. The proposed CLWA is fabricated and tested. The maximum realized gain of the novel antenna at the design frequency is about 13 dBi, and the weighted aperture efficiency of the proposed CLWA is about 0.86. There are also good agreements between the simulation and the measurement results of the proposed antenna frequency responses.

Bidirectional wide-angle waveguide grating antennas with flat-top far-field patterns for optical phased arrays.

To build advanced all solid-state LiDAR, optical phased arrays (OPAs) with a large field of view are highly desirable. As a critical building block, a wide-angle waveguide grating antenna is proposed here. Instead of aiming at the elimination of downward radiation of waveguide grating antennas (WGAs) to improve efficiencies, we in turn utilize the downward radiation and double the range of beam steering. In addition to widened field of views, the steered beams in two directions come from a common set of power splitters, phase shifters and antennas, which greatly reduces chip complexity and power consumption, especially for large-scale OPAs. Beam interference and power fluctuation in the far field due to downward emission can be decreased by specially designed SiO2/Si3N4 antireflection coating. The WGA exhibits balanced emissions in both the upward and downward directions, in which the field of view in each direction is more than 90°. The normalized intensity remains almost the same with a small variation of 10% from -39° to 39° for the upward emission and from -42° to 42° for the downward emission. This WGA is featured by a flat-top radiation pattern in far field, high emission efficiency and good tolerance to device fabrication errors. It holds good potential to achieve wide-angle optical phased arrays.

Performance Comparison of Optimization Methods for Flat-Top Sector Beamforming in a Cellular Network

The flat-top radiation pattern is necessary to form an appropriate beam in a sectored cellular network and to pro vide users with best quality services. The flat-top pattern offers sufficient power and allows to minimize spillover of signal to adjacent sectors. The flat-top sector beam pattern is relied upon In sectored cellular networks, in multiple-input multiple-output (MIMO) systems and ensures a nearly constant gain in the desired cellular sector. This paper presents a comparison of such optimization techniques as real-coded genetic algorithm (RGA) and particle swarm optimization (PSO), used in cellular networks in order to achieve optimum flat-top sector patterns. The individual parameters of flat-top sector beams, such as cellular coverage, ripples in the flat-top beam, spillover of radiation to the adjacent sectors and side lobe level (SLL) are investigated through optimization performed for 40◦ and 60◦ sectors. These parameters are used to compare the performance of the optimized RGA and PSO algorithms. Overall, PSO outperforms the RGA algorithm.

Array‐based Fabry–Pérot cavity antenna for flat‐topped radiation pattern

AbstractIn this letter, an array‐based ray tracing model and Fabry–Pérot cavity antenna covered by frequency selective surfaces (FSS) are proposed to realize the flat‐topped radiation pattern (FTRP). Based on the array‐based model, a good FTRP can be obtained by combining the initial directivity of the feed array with the additional directivity of FSS‐type partially reflective surface. By using the proposed method, a low‐cost, lightweight, simple structure and dual‐polarization Fabry‐Pérot cavity antenna with small aperture size for FTRP is designed. From the measured results, the FTRP with more than 58° beamwidth and less than 2 dB ripple level in the frequency band of 2.4 to 2.7 GHz for indoor communication are obtained.

Synthesis Method of an Orthogonal Beamforming Network With Arbitrary Ports for Shaped Beams

This article proposes a synthesis method of orthogonal beamforming networks (BFNs) with arbitrary ports. The proposed method is based on matrix decomposition theory and breakthrough the synthesized BFN number to arbitrary. It has been theoretically demonstrated that the BFN with cascading 180° hybrid couplers can synthesize shaped beams. Therefore, a BFN synthesis method that combines the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">QR</i> decomposition theory and the optimization algorithm is introduced. With the help of an optimization program, a specific power ratio of each 180° hybrid coupler in the BFN is determined. The proposed synthesis method is verified by experiments with an orthogonal <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6\times2$ </tex-math></inline-formula> BFN with flat-topped radiation patterns. Through optimization, five 180° hybrid couplers with different power ratios synthesize the proposed BFN. Results show that two flat-topped beams with a beamwidth of (32° ± 0.3°), gain ripples less than 2.5 dB, and a sidelobe level less than 12 dB are achieved. The proposed method has the advantages of high accuracy and efficiency and a simple structure, which makes it convenient for multi-beam antenna arrays in multiple-input–multiple-output (MIMO) systems.

Dual-Polarized Nonuniform Fabry–Pérot Cavity Antenna With Flat-Topped Radiation Pattern

A method to realize the flat-topped radiation pattern of Fabry&#x2013;P&#x00E9;rot cavity antenna is proposed based on the ray-tracing model. In the design, a nonuniform partially reflective surface of dielectric substrate is proposed to reduce the sidelobe level and get a fast roll-off in the operating frequency band. Besides, a dumb source array is added around the dual-polarized feed array to minimize the disparity of beamwidth between E- and H-plane. The antenna was calculated with the proposed method, simulated by the full-wave simulation, and validated by the experiment. Compared with the traditional array synthesis method, there is no need to design a complex feed network because each coaxial port is fed equally in phase and amplitude. In addition, based on the proposed method, the aperture size is small and the flat-topped beamwidth is flexible.

Design of circularly polarized flat‐top pattern with phase gradient metasurface

This article presents a metasurface (MTS) for designing a circular polarized (CP) flat-top radiation pattern using the phase compensation method. The basic idea is to generate multiple beams pointing in different directions by dividing the entire MTS into sub-regions. The MTS consists of four-layered elliptical patches encircled in a square loop printed on three dielectric substrates. The asymmetric nature of the unitcell produces two orthogonal components with equal magnitude and 90° phase difference to obtain the required linear to circular polarization conversion. The proposed MTS consists of 15 × 15 unitcells, and is fed by a rectangular patch antenna operating at 10 GHz. The flat-top pattern has been observed in the 3-D plane for u,v-polarized wave incidences at 9.9 GHz. For u-polarized incidence wave results in left-hand circular polarized (LHCP) flat-top radiation pattern with a 1 dB beamwidth of 37.5°. The axial ratio is less than 3 dB in all planes within the 1-dB beamwidth at 9.9 GHz. Similarly, for v-polarized incident wave, identical characteristics have been observed for right-hand circular polarization (RHCP), which enables the proposed structure for polarization diversity.

Analysis and Design of an X-Band Reflectarray Antenna for Remote Sensing Satellite System.

This paper presents the analysis and design of an X-band reflectarray. The proposed antenna can be used for a medium Earth orbit (MEO) remote sensing satellite system in the 8.5 GHz band. To obtain a nearly constant response along the coverage area of this satellite system, the proposed antenna was designed with a flat-top radiation pattern with a beam width of around 29° for the required MEO system. In addition, broadside pencil beam and tilted pencil beam reflectarrays were also investigated. The feeding element of the proposed reflectarray antennas is a Yagi–Uda array. The amplitude and phase distribution of the fields due to the feeding element on the aperture of the reflectarray antenna are obtained directly by numerical simulation without introducing any approximation. The required phase distribution along the aperture of the reflectarray to obtain the required flat-top radiation pattern is obtained using the genetic algorithm (GA) optimization method. The reflecting elements of the reflectarray are composed of stacked circular patches. This stacked configuration was found to be appropriate for obtaining a wide range of reflection phase shift, which is required to implement the required phase distribution on the reflectarray aperture. The antenna was fabricated and measured for verification.

Phased array antennas of coupled multimode waveguides of hexagonal cross-section with flat-topped radiation patterns

Phased array antennas of coupled multimode waveguides of hexagonal cross-section with flat-topped radiation patterns

Reactively Loaded Dielectric-Based Antenna Arrays With Enhanced Bandwidth and Flat-Top Radiation Pattern Characteristics

This paper presents an antenna array organized in sub-arrays and composed of densely spaced dielectric-based radiating elements. To reduce the number of active components required in the array beamforming network, each sub-array consists of a single active element, directly fed, and several passive reactively loaded elements. State-of-the-art implementations of such arrays are typically based on rectangular air-filled waveguide radiators which provide a limited bandwidth and support a single linear polarization only. By utilizing the dielectric-based radiators presented in this work, a significant increase in the operating bandwidth of the array can be achieved. In this case, the aforementioned reactive loading is implemented through short-circuited dielectric-filled waveguides. By optimizing the position of the short circuits, the radiation pattern of the sub-array can be controlled and synthesized according to a given mask. To create a larger design flexibility, one can design the sub-array in the presence of the adjacent sub-arrays, so achieving their effective overlapping. By employing the considered design technique, a sub-array featuring flat-top radiation pattern characteristics in combination with low side-lobe levels and high gain was developed, manufactured, and thoroughly analyzed. An additional benefit of such design choice is the possibility of supporting two orthogonal polarizations.

Odd Mathieu Functions Application to Synthesize a Multi-element Radiator Flat-topped Radiation Pattern

The paper studies synthesizing capabilities of a flat-topped radiation pattern when using the expansion of the target radiation pattern into a series in terms of odd Mathieu functions. As parameters for comparing the target and synthesized radiation patterns, we used a main-lobe width at a level of -1 dB and an irregularity of the top of the main-lobe of the radiation pattern. The sector-shaped radiation pattern has been synthesized for linear radiators of various lengths. The convergence of the coefficients of the Mathieu series in the synthesis of the sector-shaped radiation pattern has been estimated. It is shown that the use of piecewise-linear approximation of the target radiation pattern in the synthesis using a series expansion into odd Mathieu functions allows us to improve the quality of the radiation pattern formed.The task that involved finding the amplitude-phase distribution for a linear emitter with a length of 3λ, 4λ and 5λ (λ is operation wavelength) for a target radiation pattern was solved. The target amplitude distribution has the following electrical characteristics: the main-lobe width is 37.5° at a level of -1 dB and the side lobe level (SLL) is -20 dB. The synthesis procedure was performed for two cases. In the first case, the target radiation pattern is represented by a piecewise constant function with a given width. In the second case, the target pattern was specified using piecewise linear approximation of the top and slopes of the main lobe.Comparison of the radiation patterns obtained shows that in the first case, the main-lobe width of the radiation pattern at a level of -1 dB is 34°, the SLL varies from -15.6 to -17 dB, and the irregularity of the main-lobe top of the radiation pattern lies within 0.9 ... 1.2 dB. In the second case, the main-lobe width of the antenna radiation pattern at a level of -1 dB is 36.5°, the SLL is -17.5 dB, and the irregularity of the main-lobe top is 0.4 dB at most. When used, the considered under consideration enables us to obtain both the synthesized patterns for linear radiators of various lengths, and the corresponding amplitude-phase distributions and coefficients of the Mathieu series. An estimate of the convergence of the Mathieu series shows that the use of linear approximation of the target radiation pattern in some cases allows up to 2.7-fold increase in acceleration of the convergence of the Mathieu series. The accuracy of reproducing the sector-shaped pattern by the synthesis method using the expansion into odd Mathieu functions gives good results when synthesizing the amplitude-phase distribution for the linear radiators with an electric length of 5λ or more.

Flat-topped pattern synthesis of optical leaky-wave antennas

In this article, a synthesis procedure is proposed to achieve a flat-topped radiation pattern in optical leaky-wave antennas (OLWAs). In the proposed procedure, the antenna is divided into sections, each with an appropriate phase constant, length and leakage constant. By determining a proper value for these parameters, the desired flat-topped pattern is achieved. The phase constant of the sections is obtained such that their beam pointing angle follows an appropriate layout in the region of interest. Further, by introducing the same beamwidth and the same radiation power for the radiating sections, the two latter parameters, i.e., the length and the leakage constant of the sections are determined. The proposed synthesis procedure is applied to a conventional OLWA, i.e., grating waveguide (GWG), to achieve a flat-topped pattern in the angular region of -30°to -11°. Results show that the desired radiation pattern is well synthesized. Finally, the effects of beam spacing and the sections’ beamwidth on the angular rejection slope, symmetry level, -3 dB and -10 dB beamwidth are investigated. The reflection coefficient of the synthesized antenna is also examined, indicating an excellent operation below -38 dB at the entire frequency band. The proposed synthesis procedure can be applied to any type of OLWA, through which a uniform illumination can be achieved in a desired angular region.

Amplitude-Modulated Leaky-Wave Antennas

Borrowing the idea of amplitude modulation from classical communications theory, this article proposes and demonstrates a new concept of amplitude-modulated (AM) leaky-wave antennas. In the proposed concept, the traveling wave in a wave-guiding structure serves as the carrier wave whose amplitude is spatially modulated by a predefined modulating waveform to generate the desired modulated waves. Two analysis methods are subsequently developed to analyze the amplitude modulation effects. It is demonstrated that spatial amplitude modulation corresponds to shifting the spatial spectrum of the modulating wave up to the carrier spatial frequency. Therefore, one can judiciously design the modulating waveform to control the spatial frequency spectrum of the modulated waves. The spatial frequencies fallen within the radiation region are fast waves, which can radiate into free space. In this manner, the AM structure works as a leaky-wave antenna. To justify the proposed concept, two AM leaky-wave antennas based on corrugated transmission line are designed. The first one is a sinusoidally modulated AM leaky-wave antenna for high-gain application. The second is a beam-forming AM leaky-wave antenna, whose modulating waveform is synthesized to generate flat-top radiation pattern. Both simulated and measured results are given to demonstrate the concept, theory, and design of the AM leaky-wave antennas.

A Wireless Power Transmitter With Uniform Power Transfer Coverage

To avoid the performance deterioration caused by the changing placement angle of a receiving antenna, a wireless power transmitter with uniform power transfer coverage is preferred. The utilization of a transmitting antenna with flat-top radiation patterns is the most effective approach. However, the existing antennas with flat-top radiation patterns usually are complex structures and bulky sizes. To mitigate these problems, a rectangular dielectric resonator antenna (DRA) is proposed to obtain flat-top radiation patterns for the first time. Flat-top patterns are realized in both the E and H planes by combining the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">119</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sup> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">133</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sup> modes of a rectangular DRA. For validation, both linearly polarized (LP) and circularly polarized (CP) flat-topped DRAs operating at 5.2 GHz were designed, fabricated, and tested. Reasonable agreement between the measured and simulated results is observed. For the LP design, stable flat-top patterns can be maintained from 5.18 GHz to 5.24 GHz. Across the operating frequency band, the measured 3-dB beamwidths are 86° and 58° in the E and H planes, respectively, with the side lobe levels lower than -13.9 dB. For the CP design, similar flat-top radiation patterns can be found. To demonstrate the effectiveness of the proposed transmitting antenna, the LP design is used to construct a wireless power transmitter, which can provide more power and also uniform power coverage within the desired angular sector.

A wideband beam shaping reflector antenna using model predictive control

A novel method based on model predictive control (MPC) is presented for synthesis and optimization of a wide band reflector antenna with cosecant squared and flat-topped radiation patterns. The proposed system is a doubly curved reflector antenna with nonlinear dynamic equation. This article investigates design and optimization of a double ridged horn reflector antenna operating within the frequency range of 8 to 18 GHz. In order to synthesize the proposed reflector antenna, MPC is used to achieve the desired radiation cosecant pattern. This method utilizes system model and tries to find the best control effort for minimizing the cost function by predicting the future behavior. The system differential equation is comprised of first and second order derivatives, so MPC can be a good solution for synthesis of a doubly reflector antenna. MPC optimizer operates based on state space model, so the proposed system is linearized in the operating range. Maximum error, the average error and side lobe level of this method for the radiation pattern of the proposed wideband antenna respectively are 1.4, 0.9, and −20 dB. Simulation results of the radiation pattern in CST and HFSS software show that the proposed reflector antenna can be used in broadband surveillance radar systems.