Conventional Antenna Systems Research Articles

Digital metasurface for selective information distribution in the spatial domain in the THz region.

This paper presents a new, to the best of our knowledge, technique to control the flow of electron packets employing a switchable digital metasurface in the terahertz region. The proposed structure can act as a device that converts an electromagnetic (EM) wave into electron packets that can be represented in the form of digital bit sequences at the output. The top layer of the structure controls the intensity of the electron packets while the bottom layer involves the spatial distribution of the information with the help of electrical switching. The electrical switching is achieved with the application of suitable biasing across a vanadium dioxide (VO2) patch. This approach to the distribution of information helps feed the circuitry of an electronic system as per the requirement using electrical tuning, which is not possible in a conventional antenna system.

A travelling wave array system as solution for the ion cyclotron resonance frequencies heating of DEMO

Travelling wave array (TWA) antennas distributed along the periphery of the tokamak are presently considered as an ion cyclotron resonance frequencies (ICRF) heating solution for the DEMO reactor. Compared to the conventional ICRF antenna systems currently in use or designed for future machines like ITER, the TWA consists of antenna sections integrated in the breeding blanket scattered around the machine, each one fed through a variable coupler in a resonant ring configuration. Previous modelling of an antenna system for DEMO with 16 quadruple TWA sections of eight straps shows that a power capability exceeding 50 MW can be obtained in the frequency band of interest using the reference low coupling plasma profile of ITER. The described system optimizes the coupling to the plasma by providing a large number of radiating elements, which results in enhanced antenna directivity, hereby decreasing the antenna power density. This results in a maximum strap voltage amplitude of only 15 kV and maximum inter-strap voltage amplitude of 18 kV. The generators remain matched for all loading conditions: the system is totally load resilient. Following the recommendation of the work package heating and current drive Review Panel, a TWA ion cyclotron resonant heating (ICRH) system consisting of fewer sections concentrated in front of the equatorial ports is analysed in this paper and compared to the previous design. Reducing the number of sections increases the power density and its associated voltages. To couple 50 MW on the ITER density profile, voltages up to 30 kV are now required. Some aspects like the coupling between sections and its repercussion on the feeding network are briefly discussed. To assess the feasibility of the TWA fed by a resonant ring as an ICRH system for a DEMO reactor, a test on an existing medium size tokamak is under study.

Outage Analysis of Distributed Antenna Systems in a Composite Fading Channel with Correlated Shadowing

Distributed antenna systems (DASs) are known to be effective to enhance coverage, spectral efficiency, and reliability in mobile communication systems. Because multiple antennas are physically separated in space, DASs benefit from both micro- and macro-diversity, which makes DASs significantly more robust compared to conventional co-located antenna systems in fading channels. However, when multiple antennas are not dispersed enough, there exists a certain degree of correlation in large-scale fading (shadowing), which degrades the macro-diversity gain. In practice, various measurements indicate a high degree of correlation of shadowing in DASs. However, most of the previous studies on DASs have not considered the correlated shadowing and its corresponding performance loss. Motivated by this limitation, we analyze the impact of the correlated shadowing to better evaluate DAS-based schemes with dual diversity transmitters. Assuming that shadowing correlation is an exponentially decreasing function of the inter-element separation, we derive the outage probability of DAS in composite Rayleigh-lognormal shadowing channels. Also, we present numerical and simulation results, which indicate there exists an optimal inter-separation between antennas that minimizes the outage rate to balance a trade-off between macro-diversity and path loss.

Analytic and Flexible Location Determination of the Small Cell for the Heterogeneous Network

As the number of user devices growing rapidly for the current 4G communications, it is expected that the problem of energy consumption for future mobile broadband communications will be more and more seriously. Therefore, how to effectively save the energy and reduce the carbon emission are very important issues for the green communications. In this paper, an analytic and energy-efficient location determination method of the small cell access (SCA) is provided for the Heterogeneous Network. The proposed method can be applied to any kind of distribution of the users in the considered region. Combined with the Coordinated Multi-Point (CoMP) technique, the energy consumption can be further reduced. Computer simulation and outdoor field experiments are conducted to verify the performances. Results demonstrate the correctness of the derivatives and the proposed method outperforms than the compared literature methods. According to the simulation results, the proposed method with the CoMP technique can save about 70% energy for the conventional co-located antenna system architecture and 20% compared with the uniformly distributed arrangement SCA method.

Efficiency Improvement of Vehicular Antenna Systems for Ubiquitous Intelligent Systems

This paper describes the design of a high-efficiency vehicular roof-mounted antenna for wireless access for vehicular environment (WAVE) communication systems used for ubiquitous intelligent systems. The main objective of the ubiquitous intelligent system’s automotive IT technology is to enhance the connectivity among vehicles to ensure seamless communication and to reduce the initial access time using high-performance antenna systems. The efficiency of WAVE communication systems used for ubiquitous intelligent systems depends on the antenna efficiency. The proposed vehicular antenna for WAVE communication systems shows an improvement of approximately 4.77 dB in the return loss, as compared with a conventional antenna system.

Cooperative Diversity Technique Using Spatial Phase Coding Based on OFDMA System

Transmit diversity generally requires more than one antenna at the transmitter. However, many wireless devices are limited by size or hardware complexity. Cooperative diversity techniques were proposed to overcome this limitation. Cooperative communication has been widely investigated to improve the performance of wireless communication. Unfortunately, most existing cooperative schemes have the common fault of decreased transmission rate because the destination should receive the decodable compositions of symbols from the source and the relay. In this letter, we propose a new cooperative model that uses spatial phase coding (SPC) for orthogonal frequency division multiple access (OFDMA). This technique is free from the rate-loss and allows seamless cooperative communication while its diversity gain matches that of the conventional multiple antenna technique. The proposed technique is evaluated in terms of bit error rate (BER) and simulation results show that the proposed cooperative scheme approaches the performance of conventional multiple antenna system when the link between users is guaranteed.

Design of Miniaturized Fractal RFID Tag Antenna with Forced Impedance Matching

A new optimization based-methodology for miniaturizing RFID tag antenna is introduced. In this paper, the particle swarm optimization (PSO) technique in conjunction with CST Microwave Studio electromagnetic simulator are used to design a miniaturized fractal antenna having perfect impedance matching with the tag chip. The design does not need any additional loading or matching network and hence yields relatively lower cost and smaller antenna size compared with conventional tag antenna systems. A combination of two objective functions related to power reflection coefficient and antenna area are used for optimizing the antenna. The design methodology is applied to a 3rd-order Minkowski fractal nested-slot patch antenna and yields 90% area reduction compared with the reference (non-fractal) counterpart.

Antenna Placement Optimization for Distributed Antenna Systems

In this paper, we propose new algorithms to determine the antenna location for downlink distributed antenna systems (DASs) in single-cell and two-cell environments. We consider the composite fading channel which includes small and large scale fadings. First, for the single-cell DAS, we formulate the optimization problem of distributed antenna (DA) port locations by maximizing the lower bound of the expected signal to noise ratio (SNR). In comparison to the conventional algorithm based on the squared distance criterion which requires an iterative method, our problem generates a closed form solution. Next, for the two-cell DAS, we propose a gradient ascent algorithm which determines the optimum DA locations by maximizing the lower bound of the expected signal to leakage ratio (SLR). In our work, we consider selection transmission, maximal ratio transmission and zero-forcing beamforming (ZFBF) under sum power constraint and study equal gain transmission and scaled ZFBF under per-antenna power constraint. Simulation results show that our proposed algorithms based on both the SNR and the SLR criteria offer a capacity gain over the conventional centralized antenna systems.

General Purpose Wireless Communication System Using Data Acquisition

A sensor-enabled and RFID-integrated, Wireless Data Acquisition System (WDAS) that has similar functionality as multiple input multiple output (MIMO) systems for health-care applications has been developed, simulated and implemented. The system can accept various measurements via sensors placed on patients or elders and transmit information wirelessly to base station at a remote location. A microcontroller is used to control and process the signals submitted from sensor-enabled RFID devices using sequential logic. Processed signals are then sent to single receiver and transmitter pair instead of conventional MIMO antenna systems. This reduces the cost significantly in comparison to existing systems. It has been shown that the data transmitted from measurement locations can be acquired at the base station located 20 mile away. Data acquisition system (DAQ) is used to determine the measured value, apply the required statistics and display information to health-care professional at the base station. The system developed can be used for health-care applications including nursing homes in rural areas where access is difficult.

SWITCHABLE DISTANCE-BASED IMPEDANCE MATCHING NETWORKS FOR A TUNABLE HF SYSTEM

Distance-based impedance matching networks for a tunable high frequency (HF) system are presented in this paper for the improved performance. The transmitting antenna for a HF system with an operating frequency of 13.56MHz consists of a two-turn loop and three channel impedance matching networks corresponding to the distance of the receiving antenna. Each impedance matching network maximizes the system performance such as uniform power e-ciency and reading range at speciflc distance between a transmitting and a receiving antenna. By controlling the distance-based matching networks, the power e-ciency of the proposed antenna improves by up to 89% compared to the conventional antenna system with the flxed matching (FM) condition for distances, and the reliable reading range according to the impedance matching conditions is also increased. The proposed technique is applicable for near fleld communication (NFC), radio frequency identiflcation (RFID), or wireless power transfer (WPT) devices.

Slim Luneburg lens for antenna applications

Luneburg lens is a marvellous optical lens but is extremely difficult to be applied in any practical antenna system due to its large spherical shape. In this paper, we propose a transformation that reduces the profile of the original Luneburg lens without affecting its unique properties. The new transformed slim lens is then discretized and simplified for a practical antenna application, where its properties were examined numerically. It is found that the transformed lens can be used to replace conventional antenna systems (i.e. Fabry-Perot resonant antennas) producing a high-directivity beam with low side-lobes. In addition, it provides excellent steering capabilities for wide angles, maintaining the directivity and side-lobes at high and low values respectively.

Low Complexity Hybrid Smart Antenna with Directional Elements over Frequency Selective Fading Channel

In this paper, a low complexity hybrid smart antenna system with directional elements and reduced-size digital beamformer is proposed to combat the inter-symbol interference (ISI) problem over frequency-selective fading channels. The conventional smart antenna systems with omni-directional elements utilize the full-size digital beamformer to suppress interference and obtain the optimum performance. However, the proposed hybrid smart antenna system with directional elements can split the linear receive array into two subarrays. One subarray contains the elements with no ISI, which can be processed with a simple maximum ratio combiner (MRC). The second subarray includes the elements with the ISI interference, which require the use of a reduced-size optimum beamformer for interference suppression. Finally, the outputs of the two subarrays are combined for optimal detection of the transmitted signals. Simulation results confirm that the proposed low complexity hybrid smart antenna system can provide robust performance under the multipath fading channel with ISI, and outperform the conventional smart antenna systems due to the use of directional antennas and utilization of multipath diversity gain.

High altitude airborne cellular base stations antenna analysis

Obtaining continual mobile communication coverage over two or more disparate regions from an airborne platform utilizing a deployable cellular base station has proven to be challenging due to the resulting signal spatial structure and signal gain observed from the mobile ground users. A two-dimensional aircraft simulation environment has been developed to evaluate the optimal link budget of an antenna system coupled with a Code Division Multiple Access (CDMA) base station positioned above 45,000 feet in a designated elliptical orbital pattern in an effort to acquire broader and longer communication coverage. This will analyze the signal excess results of both an omni-directional conventional antenna system (CAS) and a switched-beam smart antenna system (SBSAS) with multiple mobile ground users present. Collectively, these results constitute a basis for low-risk implementation for a high altitude airborne deployable cellular base station.

Multicomponent receiver architectures for GPS interference suppression

The global positioning system (GPS) is a one-way satellite-based navigation system employing spread-spectrum techniques that is widely used for commercial and military applications. Although the very low signal-to-noise ratio (SNR) is handled by the large spreading gain, GPS is susceptible to high-power interference signals and various types of jammers. We propose multicomponent receiver architectures for GPS interference suppression. A conventional antenna system is first considered which utilizes a minimum-variance distortionless-response (MVDR) beam former and assumes that the GPS signal angle of arrival (AOA) and the antenna model are known at the receiver. However, this receiver is sensitive to AOA estimation errors and can have a high computational complexity. This sensitivity problem is eliminated by a multicomponent system based on a multistage matched filter (MF). Since this MF receiver also has a high computational complexity because the jammer AOAs must be estimated, we introduce a blind interference canceler based on the constant modulus (CM) array that is insensitive to AOA estimation errors and has a low computational complexity. Computer simulations are provided to illustrate the performance of the various systems for interference suppression in example signal scenarios.

Printed collinear two‐antenna element for WLAN access points in a MIMO system

AbstractA printed collinear two‐antenna element suitable for application in a wireless local area network (WLAN) access point in a multi‐input multi‐output (MIMO) system is presented. The printed element comprises one dipole antenna and one monopole antenna, both printed in a collinear configuration on a narrow FR4 substrate of width 12 mm and length 120 mm and showing good omnidirectional radiation characteristics. It has been found that an antenna system formed by using two proposed elements spaced 75 mm or larger can have good isolation (better than −20 dB) between any two of the four antennas in the two proposed elements. With the comparison to the conventional antenna system formed by four discrete antennas, the antenna system with two proposed elements shows a much smaller lateral length. This characteristic makes the proposed collinear two‐antenna element advantageous for application in a MIMO system. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 930–933, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21522

Multi-band, multi-polarisation reflector-reflectarray antenna with simplified feed system and mutually independent radiation patterns

An antenna system that combines reflectarray and conventional reflector technology is suggested for multi-band, multi-polarisation applications. This hybrid technology gives rise to the significant simplification of the feed system and relaxation of filtering requirements. The suggested design does not introduce additional volumetric requirements in comparison to equivalent conventional antenna systems. The proposed system is capable of maintaining mutually independent radiation patterns for each of its operating bands. A prototype that consists of a conventional ku-band offset reflector and a ka-band reflectarray was designed, fabricated, and tested. Close to 60% and 40% aperture efficiencies were realised in the lower and upper bands, respectively. The design procedure and experimental results are presented.

Experimental studies of direction of arrivals using a smart antenna testbed in wireless communication systems

AbstractThis paper presents some preliminary results from experimental studies on space‐division‐multiple‐access (SDMA) for wireless communications. A smart antenna system utilizing direction‐of‐arrival (DOA)‐based beamforming techniques can enhance signal quality by reducing co‐channel interference from mobiles located at angles spatially distinct from the base station. Adopting both smart uplink and downlink beamforming, a communication system with an antenna array can increase the cell coverage of a base station and significantly boost capacity compared with conventional antenna systems. However, successful implementation of DOA‐based beamforming techniques depends on the DOA characteristics. This paper presented the feasibility of direction finding and DOA variation with respect to frequency. Furthermore, the angle spread was studied for selected environments. The results demonstrate the feasibility of applying proposed smart antenna system utilizing DOA‐based beamforming algorithm for increasing channel capacity and improving system performance in frequency‐division‐duplex (FDD) wireless communication systems. Copyright © 2003 John Wiley & Sons, Ltd.

Performance evaluation of mobile radio slotted ALOHA with fixed multibeam antennas

In this paper, we report our investigation into the effect of using fixed multibeam antennas on the performance of the slotted ALOHA protocol with capture in a mobile communications environment with Rayleigh and Log-normal fading. We consider the configuration where multiple receivers are present at each base station and calculate the capture probability, its asymptotic value as the number of colliding packets tends to infinity, and throughput when multiple receivers are used. The results demonstrate that by using fixed multibeam antennas, we can achieve higher performance in terms of capture probability and throughput when compared to a conventional antenna system using the slotted ALOHA protocol.

Simple method of calibration of conventional sodar antenna system

Abstract The accurate estimation of sodar antenna parameters, back-scattering cross-section and a knowledge of acoustic absorption in the atmospheric air are needed in case structure parameters are to be computed. In the paper a simple method using a theoretical antenna directivity pattern, together with measurements of transduction characteristics of the acoustic transducer has been suggested. The method has been used for two sodars belonging to the Russian Academy (Sodar Latan-I) and the National Physical Laboratory, New Delhi, The theoretically and experimentally determined directivities of the Sodar Transducer Systems have been compared and it has been found that they coincide rather satisfactorily within the angles at which the paraboloids of sodars are seen from their respective foci. Computed thermal structure parameter values using Sodar Latan-I based on the above approach have been found to be comparable with the values computed from microthermal data collected simulaneously at the same place

Using elevated radials in conjunction with deteriorated buried-radial ground systems

Computer-modeling exercises performed indicate that it is possible to add a group of four elevated radials to a pre-existing conventional AM-broadcast vertical monopole antenna system in order to restore performance to its original level (or better) in situations where the buried-radial ground system has been damaged. A wide variety of different configurations for the elevated radials are examined, including variations in orientation, length, and height above ground. It is stressed that extensive outdoor testing should be performed in order to verify these computer predictions. The computer software used is the Numerical Electromagnetics Code. >