Antenna Problems Research Articles

MODERN ANTENNA DESIGN USING MODE ANALYSIS TECHNIQUES

In this paper, the modal theory of antennas is re-visited, believing that it brings invaluable information towards facilitating the design of multi-feed multi-band antennas. First, some subtle changes are proposed to enhance the applicability of the theory. Next, using some efficient computational techniques, the proposed formulations are shown to predict, to a very high accuracy, the input impedance of any antenna under study. This greatly simplifies the antenna problem and focuses design efforts on finding the appropriate complex resonance frequency to cover a required band. Finding the appropriate feed location is then a matter of extracting the corresponding impedance map for this antenna through simple field manipulations.

Performance Comparison of RFID Tag at UHF Band and Millimeter-Wave Band

The ultra high frequency (UHF) band spectrum will likely be congested in near future since the next generation wireless as well as Radio Frequency Identification (RFID) system users will witness the use of UHF band technology with increased demand of bandwidth, bit rate, frequency spectrum and power consumption. The alternate solution is the use of millimeter-wave band technology. It is possible to improve data throughput, range resolution and multi-user capability in mm-wave band RFID system. ‘Higher power reception efficiency and lower side lobe level (SLL) of radiation pattern’ is required for RFID system that will increase the tag range and transmission bit rate. At the same time lower SLL will minimize the interference level. Beam pointing error is another problem of UHF band antenna which reduces the tag range and bit rate. These problems can be minimized by using large number of antenna elements. But with UHF band signal it is practically difficult to construct large array antenna; since the array size becomes tremendously larger with the increase of antenna elements. ‘Higher power reception efficiency and lower SLL’ can practically be obtained by using non-uniform power distribution of large number of antenna elements in millimeter wave band. A new and technically better method of beam forming by implementing the concept of staircase power distribution (SPD) of antenna elements at 60 GHz has been investigated and presented in the paper. The SPD method is compared with Gaussian edge tapering method. It was found that the maximum SLL (MSLL) is the lowest in case of SPD. The beam efficiency of SPD is also equivalent to that of Gaussian edge tapering method. It is easier to fabricate a larger number of antenna elements within smaller area with SPD at 60 GHz system; since the antenna size is smaller and the number of different power distribution in SPD case is less and stepwise uniform. Uniform and less number of different power distribution of SPD also minimizes other technical errors.

Radiation pattern simulation of antenna array problem with perfectly electrically conducting object in arbitrary shape using novel hybrid method of equivalence principle algorithm and physical optics

A hybrid method combining the equivalence principle algorithm (EPA) with physical optics (PO) is proposed to solve electromagnetic radiation of an antenna array with perfectly electrically conducting (PEC) object of arbitrary shape. The main idea of this approach is based on the domain decomposition method which is a scheme for multi-scale problems. An EPA can simulate antenna array accurately, and PO is an asymptotical method to obtain current distribution on a PEC object of arbitrary shape as an electrically large problem. For an antenna array with identical elements, the equivalence principle operator only needs to be calculated and be stored once. Compared with the original EPA, this approach performs with higher efficiency and fewer iterations with acceptable accuracy. Numerical results demonstrate the feasibility of the hybrid method.

MEMS Reconfigurable Optimized E-Shaped Patch Antenna Design for Cognitive Radio

Reconfigurable antennas offer attractive potential solutions to solve the challenging antenna problems related to cognitive radio systems using the ability to switch patterns, frequency, and polarization. In this paper, a novel frequency reconfigurable E-shaped patch design is proposed for possible applications in cognitive radio systems. This paper provides a methodology to design reconfigurable antennas with radio frequency microelectromechanical system (RF-MEMS) switches using particle swarm optimization, a nature-inspired optimization technique. By adding RF-MEMS switches to dynamically change the slot dimensions, one can achieve wide bandwidth which is nearly double the original E-shaped patch bandwidth. Utilizing an appropriate fitness function, an optimized design which works in the frequency range from 2 GHz to 3.2 GHz (50% impedance bandwidth at 2.4 GHz ) is obtained. RF-MEMS switch circuit models are incorporated into the optimization as they more effectively represent the actual switch effects. A prototype of the final optimized design is developed and measurements demonstrate good agreement with simulations.

Compact Low Weight High Gain Broadband Antenna by Polarization-Rotation Technique for X-Band Radar

Less efficiency and gain is achieved by existence of aperture blocking phenomena in cassegrain antenna caused by the presence of subreflector or antenna feed. Also, length of feed cables causes delay which is another undesirable problem in antennas, since errors and less precision of detecting targets are created. To overcome these problems, low weight and compact optimized polarization-rotation monopulse cassegrain antenna is designed in this paper. The goal of our proposed rotating antenna is achievement of sum and difference patterns for target tracking in monopulse radar. In our work, left part of hyperbolic subreflector instead of right one has been used for reducing size of the antenna. The antenna is fabricated by grid wires instead of solid sheet metal reflectors and with composite technology for decreasing its weight. Width and volume of the antenna reduce by about 50% in comparison to other reflector antennas. This antenna has been simulated and manufactured in X-band and simulation data are in good agreement with measured ones. The antenna has the average gain of 35 dB from 8.5 up to 9.5 GHz. Also the antenna feed bandwidth is more than 50% and the antenna has efficiency of about 50% from 8 up to 10 GHz.

三路太赫兹光导天线的功率合成技术

For the limited power capacity problem of single photoconductive antenna,we use photoconductive antenna power combining technology to research high power and ultra-broadband terahertz radiation. By constructing a power combining system of three-way photoconductive antenna,using500 μm aperture dipole photoconductive antenna as the object,we studied the power combining technology. When the optical path differences of terahertz emitted by three-way 500 μm aperture photoconductive dipole antenna are the same,the power combined time-domain spectral reaches to maximum peak,the degree of temporal coherence up to 90. 6%,the output power of terahertz is improved efficiently.

Synthesis of thinned concentric circular antenna arrays using teaching-learning-based optimization

In this article, the design of thinned concentric circular antenna arrays CCAAs of isotropic radiators with optimum side lobe level SLL reduction is studied. The newly proposed global evolutionary optimization method; namely, the teaching-learning-based optimization TLBO is used to determine an optimum set of turned ON elements of thinned CCAAs that provides a radiation pattern with optimum SLL reduction. The TLBO represents a new algorithm for optimization problems in electromagnetics and antennas. It is shown that the TLBO provides results that are somewhat better than those obtained using other evolutionary algorithms, like the firefly algorithm and biogeography based optimization. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:443-450, 2014.

Reply to “Comments on `Superdirective-Type Near Fields in the Method of Auxiliary Sources'”

Summary form only given, as follows. We would like to Dr. Skobelev for bringing to the authors' attention the paper by N.P. Malakshinov and V.G. Yerikhov: On one numerical method for solving diffraction problems in Antennas, no. 25, pp. 53-65, 1977 (in Russian), which, to the best of their knowledge, has not been translated into English. Having now located and read the interesting paper by N.P. Malakshinov and V.G. Yerikhov the authors' of the above-named article (ibid., vol. 60, no. 6, pp. 3056-3060, June 2012) agree with Dr. Skobolev that the IEEE article discusses relations between the Method of Auxiliary Sources (MAS) and superdirectivity in more detail than in the Russian article. In the IEEE article the authors go beyond the rather obvious similarity that both MAS and superdirective arrays exhibit oscillating currents. Rather, they focus on developing asymptotic formulas for the near field that allow one to distinguish the superdirective-type behaviors in MAS from effects due to roundoff. They cannot agree with Dr. Skobelev's comment ... creates the impression that its authors were the first and only ones who detected the indicated analogy; in fact, in the Acknowledgment of the Russian article Malakshinov and Yerikhov thank Professor Ramakrishna Janaswamy for first suggesting the relationship between MAS and superdirectivity.

Simplified evaluation of the reduced kernel to solve the radiation problem of a cylindrical antenna

This paper presents simplified expressions regarding the radiation problem of a cylindrical straight antenna using the method of moments with the so-called reduced kernel or approximate.

Design of wide-beam antenna using dynamic multi-objective BBO/DE

Because the requirements of antennas get more and more complicated, an effective evolutionary algorithm for solving complex antenna problems is necessary. The hybrid biogeography-based optimisation with differential evolution BBO/DE and dynamic multi-objective technique are combined into dynamic multi-objective BBO/DE, which is aimed at improving the global search ability in solving antenna optimisation problem. We then used the effective algorithm to solve a challenging wide-beam antenna problem with beam width of 140 degrees. A small antenna with only seven wires, however, with 20 variables and 4,322 constraints, has been designed, and an acceptable one, which is satisfied in real application, has been obtained.

CIRCULAR ANTENNA ARRAY DESIGN BY USING EVOLUTIONARY SEARCH ALGORITHMS

Evolutionary Search Algorithms (EA) have been inten- sively used in solving numerical optimization problems. Since design of antenna arrays is a numerical optimization problem, EAs have been intensively used in solving antenna arrays design problems. Although EAs are widely used in antenna array design problems, a performance comparison study of the intensively used EAs for circular antenna ar- ray design problem has been scarcely studied. In this paper, 3 difierent circular antenna array design problems have been solved by using 15 difierent evolutionary search algorithms (i.e., ABC, ACS, BSA, CK, CLPSO, CMAES, DE, E2-DSA, EPSDE, GSA, JADE, JDE, PSO, SADE, S-DSA). The objective function designed for solution of the relevant circular antenna array design problems ensures minimization of side lobe levels, acquisition of maximum directivity, and null control of the non-uniform, planar circular antenna array. Obtained statistical analysis results show that S-DSA solves the relevant circular antenna array design problems statistically better than the other evolutionary algorithms used in this paper.

Topology Optimization of Metallic Antennas

We introduce an approach to carry out layout optimization of metallic antenna parts. An optimization technique first developed for the optimization of load-bearing elastic structures is adapted for the purpose of metallic antenna design. The local conductivity values in a given region are used as design variables and are iteratively updated by a gradient-based optimization algorithm. Given a set of time-domain signals from exterior sources, the design objective is here to maximize the energy received by the antenna and transmitted to a coaxial cable. The optimization proceeds through a sequence of coarsely-defined lossy designs with successively increasing details and less losses as the iterations proceed. The objective function gradient is derived based on the FDTD discretization of Maxwell's equations and is expressed in terms of field solutions of the original antenna problem and an adjoint field problem. The same FDTD code, but with different wave sources, is used for both the original antenna problem and the adjoint problem. For any number of design variables, the gradient is evaluated on the basis of only two FDTD simulations, one for the original antenna problem and another for the adjoint field problem. We demonstrate the capability of the method by optimizing the radiating patch of both UWB monopole and microstrip antennas. The UWB monopole is designed to radiate over a wide frequency band 1-10 GHz, while the microstrip patch is designed for single and dual frequency band operation. In these examples, there are more than 20,000 design variables, and the algorithm typically converges in less than 150 iterations. The optimization results show a promising use of the proposed approach as a general method for conceptual design of near-resonance metallic antennas.

Response of plasmonic resonant nanorods: an analytical approach to optical antennas

An analytical model of the response of a free-electron gas within the nanorod to the incident electromagnetic wave is developed to investigate the optical antenna problem. Examining longitudinal oscillations of the free-electron gas along the antenna nanorod a simple formula for antenna resonance wavelengths proving a linear scaling is derived. Then the nanorod polarizability and scattered fields are evaluated. Particularly, the near-field amplitudes are expressed in a closed analytical form and the shift between near-field and far-field intensity peaks is deduced.

Numerical Solutions of the Integral Equation for Excitation-Transmission-Radiation in Aperture Antenna

The numerical method of the volume-surface integral equation has been used to model the electromagnetic excitation and propagation problems of the waveguide-fed aperture antenna. The mode-matching method has been used to describe the impedance marching situation at the exciting aperture. The excitation conditions were established based on the expansion of the waveguide modes and the equality principle of electromagnetics. The multi-level fast multi-pole algorithm is applied to speed up the matrix-vector multiplication and reduce the memory requirement of the method of moment. The numerical solutions of the electromagnetic transmission and radiation of an offset paraboloidal reflector antenna have been given. It has been demonstrated that the method proposed by this article is able to provide the valid and accurate numerical solution for the electromagnetic propagation and radiation problems of an aperture antenna with an arbitrary shape, composite metallic and material structure, and electrically large size.

H− radio frequency source development at the Spallation Neutron Source

The Spallation Neutron Source (SNS) now routinely operates nearly 1 MW of beam power on target with a highly persistent ∼38 mA peak current in the linac and an availability of ∼90%. H(-) beam pulses (∼1 ms, 60 Hz) are produced by a Cs-enhanced, multicusp ion source closely coupled with an electrostatic low energy beam transport (LEBT), which focuses the 65 kV beam into a radio frequency quadrupole accelerator. The source plasma is generated by RF excitation (2 MHz, ∼60 kW) of a copper antenna that has been encased with a thickness of ∼0.7 mm of porcelain enamel and immersed into the plasma chamber. The ion source and LEBT normally have a combined availability of ∼99%. Recent increases in duty-factor and RF power have made antenna failures a leading cause of downtime. This report first identifies the physical mechanism of antenna failure from a statistical inspection of ∼75 antennas which ran at the SNS, scanning electron microscopy studies of antenna surface, and cross sectional cuts and analysis of calorimetric heating measurements. Failure mitigation efforts are then described which include modifying the antenna geometry and our acceptance∕installation criteria. Progress and status of the development of the SNS external antenna source, a long-term solution to the internal antenna problem, are then discussed. Currently, this source is capable of delivering comparable beam currents to the baseline source to the SNS and, an earlier version, has briefly demonstrated unanalyzed currents up to ∼100 mA (1 ms, 60 Hz) on the test stand. In particular, this paper discusses plasma ignition (dc and RF plasma guns), antenna reliability, magnet overheating, and insufficient beam persistence.

Generalized Multilevel Physical Optics (MLPO) for Comprehensive Analysis of Reflector Antennas

Recent developments of the multilevel physical optics (MLPO) algorithm aiming at the comprehensive analysis of complex reflector antenna systems are presented. The physical theory of diffraction (PTD) line integral along the rim of a reflector is combined with the physical optics (PO) surface integral within the multilevel algorithm. The multilevel scheme is also generalized to combine fields radiated by various components of different sizes, as encountered in complex antenna systems with multiple feeds and/or reflectors. Comparison with published results demonstrates the ability of the MLPO algorithm to cope accurately and efficiently with realistic reflector antenna problems.

Investigations on the synthesis of uniform linear antenna array using biogeography-based optimisation techniques

This paper presents the use of biogeography-based optimisation (BBO) algorithm for uniform linear antenna array (ULA) synthesis using amplitude only control method. BBO is a new evolutionary algorithm (EA) proposed by Dan Simon in the year 2008. The first objective of this paper is to optimise the excitation magnitude of array elements to minimise the maximum side lobe levels. Second objective is to place nulls at specific directions for the optimised pattern by optimising a weight parameter. We review classic BBO and modified biogeography-based optimisation (M-BBO) with two migration models namely linear and sinusoidal. Several simulation experiments are conducted on ULA using BBO techniques to minimise the maximum side lobe level (SLL) imposed with broad nulls. We compare the results of simulation case studies of classic BBO and M-BBO with other EAs such as ACO, GA and StudGA. Best performance is achieved using BBO techniques compared to other EAs for our design problem. The major aim of our investigation is to expose BBO to the EM community and demonstrate its great potential in antenna array design optimisation problem.

EMC ANALYSIS OF ANTENNA SYSTEM ON THE ELECTRICALLY LARGE PLATFORM USING PARALLEL MoM WITH HIGHER-ORDER BASIS FUNCTIONS

Currently, more and more practical engineering applica- tions place antenna system on the electrically large platform. This paper deals with the problem of antennas mounted on large platform from two aspects | radiation pattern and system electromagnetic com- patibility (EMC). To achieve an accurate and efiective computation, this paper applies method of moment (MoM) with Higher-order basis functions solver with large-scale parallel computation technique. And flnally some real-life examples are presented to describe how to install antennas on the platform reasonably.

ANALYSIS OF MULTI-SCALE PROBLEM ABOUT ANTENNA MOUNTED ON ELECTRICALLY LARGE PLATFORM BY USING CONNECTED EPA-PO

In this paper, a hybrid method combining equivalence principle algorithm with physical optics is proposed to solve the radiation problem of antenna mounted on electrically large platform. It is based on domain decomposition method which is a scheme for multi- scale problems. Equivalence principle algorithm can simulate antenna accurately, and physical optics is an asymptotical method to obtain current distribution on the electrically large platform. Continuity of currents is considered when the conductor on the platform is decomposed into two parts by the equivalence surface. In addition, a preconditioning for the hybridization of equivalence principle algorithm and physical optics is discussed. Numerical results demonstrate the feasibility of the hybrid method.

Taper-Walled Linearly Tapered Slot Antenna

Direct coupling among antenna elements is one of the critical problems of array antennas in near-field imaging systems. To mitigate the coupling, we propose taper-walled linearly tapered slot antenna (taper-walled LTSA) to be used in our adaptive ground penetrating radar (GPR) system for visualization of plastic landmines. It is based on the conventional walled LTSA, but the sidewall edges are curved at the aperture and connected to side slits. We analyze the characteristics of the proposed antenna in simulation, and demonstrate in experiment the reduction of the direct coupling in a wideband from 7.2 to 12 GHz which covers the observation frequency of our stepped-frequency adaptive landmine visualization system. The idea is directly usable also in other frequency bands.