Shaped Beam Reflector Research Articles

Simultaneous Optimal Design Method of Primary Radiator and Main Reflector for Shaped Beam Antennas

Shaped beam reflector antennas are widely used because they can achieve a shaped beam even with a single primary feed. Because coverage shapes depend on service areas, optimum primary radiators and reflector shapes are determined by the service areas. In this paper, we propose a simultaneous optimal design method of the primary radiator and reflector for the shaped beam antenna. Particle swarm optimization and the conjugate gradient method are adopted to optimize the primary radiator and reflector. The design method is applied to Japan coverage to verify its effectiveness.

A comparison between GA, PSO, and IWO for shaped beam reflector antennas

This paper presents a comparison between three evolutionary algorithms (EAs) for pattern synthesis of offset reflector antenna fed by a planar array of horn antennas. To perform the optimization process, an elliptical-shaped beam in the U–V plane (U = sinθ cosφ and V = sinθ sinφ) is considered as the desired far-field radiation pattern. To attain the appropriate excitation value for array elements, three conditions are considered: (1) variable amplitude (with uniform phase distribution), (2) variable phase (with uniform amplitude distribution), and (3) variable amplitude and phase excitation. Obtaining the appropriate excitation value based on the mathematical methods is always complicated and time-consuming. Therefore, genetic algorithm (GA) and particle swarm optimization (PSO) as two well-known EAs have been used widely for different applications and shown the promise to solve complicated problems. This paper compares these two EAs with invasive weed optimization (IWO) which is robust and has simple and powerful process with few tuning parameters. We found that for pattern synthesis of multi-feed reflector antenna in different conditions, IWO can provide accurate and comparable results with GA and PSO methods at approximately same iteration number. The convergence diagrams as well as the optimized radiation patterns for different conditions are presented and compared for GA, PSO and IWO.

Two-dimensional synthesis and optimization of a broadband shaped beam reflector antenna using IWO and PSO algorithms

A new technique for broadband shaped beam reflector antennas synthesis is presented. The surface of the shaped reflector is represented by a set of orthogonal Jacobi-Fourier expansion functions. To achieve a cosecant squared pattern in the elevation plane and a pencil beam in the azimuth plane, the expansion coefficients are optimized using invasive weed optimization and particle swarm optimization algorithms. High accuracy is achieved by combining optimization tools and analysis methods such as physical optics and integral equation. Besides, in the optimization procedures, a complex object function is used to achieve the desired performance over the entire 26-40 GHz operating bandwidth. The simulation results via FEKO and CST Microwave Studio software packages prove the validity and versatility of this technique for solving shaped reflector synthesis problems. There are several features that distinguish this technique from the previous methods. First of all is the wide bandwidth. The second is its ability to shape the radiation patterns in the elevation and azimuth planes simultaneously two-dimensional synthesis. Moreover, compared with other techniques, the proposed method allows achieving extra desired features such as high directivity, low sidelobe levels, and small ripples in the shaped beam region. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:129-140, 2015.

Broadband Approximation of Radiation Patterns for Doubly Curved Reflector Antennas [Antenna Designer's Notebook

Avery simple broadband approximation of the radiation patterns for shaped-beam reflector antennas with a primary feed (rectangular horn), producing cosine amplitude and uniform phase aperture distributions, is presented. Typical values, beamwidth changes, sidelobe levels, and aperture efficiencies are given for frequency changes up to approximately three times the operating frequency. A comparison of the approximated and measured patterns of doubly curved reflector antennas shows that the given approximation can be reliably used for analyses of pattern changes due to very broad frequency changes. This is very valuable for electromagnetic compatibility analyses, both from the electromagnetic interference and susceptibility points of view.

Smooth aperture distribution synthesis for shaped beam reflector antennas

A method of synthesising smooth aperture amplitude and phase distributions from a prescribed far-field radiation pattern is proposed. A geometric optics (GO) solution of the problem, which gives a starting point for the final physical optics (PO) optimisation, is obtained using the Monge-Ampère approach of Westcott. During PO optimisation a derivative condition is invoked to control the smoothness of the aperture distributions.

Application of spherical wave expansions to direct GO far field synthesis

Diffraction effects which arise in the direct far field geometrical optics synthesis of shaped beam reflector antennas are examined. A spherical wave expansion technique is introduced which allows the optical coverage area and reflector dimensions to be specified in Westcott's complex co-ordinate synthesis technique. Examples are given of the method when applied to the synthesis of typical beam shapes encountered in satellite communications.

Synthesis of shaped-beam reflector antenna patterns

The paper describes the synthesis of shaped-beam dual-reflector antenna patterns using two methods. In the first, for a prescribed far field the antenna aperture field is obtained initially and then a Geometric Optics synthesis method used to define the reflector coordinates. In the second method an optimisation procedure is employed to shape the reflectors directly, so as to generate, through Physical Optics, the desired far field. The two methods are compared for the pattern corresponding to the EUTELSAT 2 spacecraft. Close agreement is found and differences ascribed to initial constraints.

Direct far-field GO synthesis of shaped beam reflector antennas

Direct far-field GO synthesis of shaped beam reflector antennas

Feed network for dual beam reflector antennas

A primary feed network for doubly curved shaped-beam reflector antennas is described which allows simultaneous signal reception on two distinct elevation plane patterns such that the underside falloff separation between a fixed lower beam and a higher beam can be substantially varied in a lossless manner. A three-element feed array is employed wherein two elements of the array are interconnected by means of a sum-difference hybrid. The sum port generates the fixed low beam while the difference port generates an orthogonal beam pattern suitable for RF combining with an independent high beam generated by the third array element. Adjustment of the combining amplitude and phase relationships permits the variation of the underside falloff separation. The fixed low beam is, of course, also used for transmission at high power. Design parameters for a typical surveillance radar application axe discussed for a linearly polarized case. Calculated antenna patterns and free-space coverage diagrams are presented. The complexities of extending the feed network concept to handle switchable linear/circular polarization cases and an integral directional beacon pattern for L band systems are indicated.

Dual vertical beam properties of doubly curved reflectors

An investigation has been made of the vertical-plane dual-beam properties of a doubly curved shaped-beam reflector to provide design information relative to possible modifications for a large class of surveillance antennas (in particular, the cosecant-squared family) in order to improve their performance when working in the presence of serious ground clutter problems. Experimental results obtained with an X -band model reflector utilizing various dual-feedhorn geometries are presented. Measured secondary patterns demonstrating several important performance characteristics are shown for a linearly polarized situation. Measured primary patterns for the feeds which generate these results are included, Two-way radar coverage diagrams for one set of dual-beam patterns are examined in detail. These plots make it clear that for many ground clutter minimizing applications it appears desirable to mix at RF the signals received by both feedhorns.

An Improved Ground Beacon Antenna

An electromechanical scanning antenna technique is proposed to provide improved TACAN ground-beacon performance over the full 960-to 1215-Mc band.A radially symmetric, shaped-beam reflector is illuminated by an off-set, radial-pillbox horn. The horn is driven by a radial transmission line which contains a central radiator. Parasitic elements are arranged in dielectric rings positioned concentrically with the central radiator. The rings are rotated uniformly about the center line to generate an amplitude-modulated, omnidirectional azimuth pattern. The complex response of the elements controls the percentage modulation, while the geometry of the reflector and its feed independently control the shape of the elevation pattern. The antenna generates uniform azimuth modulation over the elevation angles of interest.