Adaptive antennas for mobile communications

Adaptive-antenna techniques offer the possibility of increasing the performance of mobile radio communication systems by maximising directional gain and enhancing the protection towards multipath conditions. The net effect of these techniques is to improve immunity to interference, extend the range of each cell and thus increase the system capacity. The paper presents the results of a two year research programme aimed at the development of practical adaptive-antenna signal-processing structures. Specifically, results obtained from a series of analysis and field trial activities undertaken with an adaptive antenna test bed and based around the DECT cordless standard are presented     

Wideband patch antennas for mobile communications

This paper describes a new technique for bandwidth enhancement of microstrip patch antennas. An electromagnetically coupled (EMC) feeding structure was employed to increase the bandwidth. L-strip feeding rectangular and triangular patches were simulated and tested. The obtained bandwidth (SWR2) is about 1200 MHz (52%) for the rectangular patch, while that of the triangular one is around 1300 MHz (56%). These results provide evidence that the proposed designs can be used in the DCS, PCS, UMTS, WLAN and IMT-2000 service frequency bands.     

Phased array antennas for mobile communications

An antenna system including antenna elements and a tracking method is considered a key technology in mobile communication systems. A phased array antenna has been considered the most favorite candidate because of many attractive characteristics such as a low and compact profile, high-speed tracking and potentially low cost performance for vehicle antennas in mobile communications. On the other hand, it has several such disadvantages as beam steering error, loss in feed lines and an increase of noise level in a receiving frequency band. Some of phased array antennas have already been used in satellite communications, and some of them are under development. This paper overviewed basic performance and some examples of phased array antennas for especially satellite mobile communications.     

Miniature built-in multiband antennas for mobile handsets

In this paper, we propose a new design for built-in handset antennas in that metal strips as additional resonators are directly connected with a feed strip. With the new design scheme, a quad-band antenna for covering GSM900, DCS1800, PCS1900, and UMTS2000 bands and a five-band antenna for covering GSM900, DCS1800, PCS1900, UMTS2000, and ISM2450 bands for use in mobile built-in handsets are experimentally carried out. Compared with the parasitic form with a shorted strip placed away from the main radiator in the open literature, the size of the proposed antennas can be reduced by an order of 10/spl sim/20%, which is desirable since the size of mobile phones is becoming smaller according to consumer preferences. Moreover, the impedance matching for each band of the new antennas becomes easy. The new quad-band and five-band built-in handset antennas are developed within the limits of a 36/spl times/16/spl times/8 mm/sup 3/ volume. The antennas are also analyzed using the finite-difference time-domain technique. A good agreement is achieved between measurement and simulation.     

Dipole printed array antennas for mobile radio systems

Dipole array antennas realized on the basis of radiating modules in which strip dipoles are integrated with antenna balancers of a novel structure are described. Units with reduced overall dimensions and a reduced mass, which allow substantial simplification of the construction of array antennas for mobile radio systems, are proposed.     

卫星移动通信中的电扫描阵列天线

90年代以来，卫星移动通信发展异常迅速。许多科研组织都对移动地面站中的电扫描阵列天线进行了研究。介绍了目前已经开发并应用于卫星移动通信的几种电扫描阵列天线及其技术细节。     

Microstrip annular ring slot antennas for mobile applications

An annular slot on triplate feed is discussed which is suitable for use with vehicular mobile satellite systems. The slot is excited in a higher order mode and circularly polarised to give a conical radiation pattern. The slot can operate on a high dielectric base and a superstrate improves the gain     

Lens antennas for mobile broadband systems in the millimetre-waverange

An improved antenna for a wireless mobile broadband system (e.g. as realised by Bosch as a demonstrator) is proposed. By means of a shaped dielectric lens the radiation pattern of a primary antenna (e.g. a short helical structure) can be shaped to optimise the power distribution across an indoor cell. The calculated performance of lenses designed for the 30 and 60 GHz bands by using geometric optics shows good agreement with measured results     

Smart antennas for mobile communication systems: benefits andchallenges

Spatial filtering using adaptive or smart antennas has emerged as a promising technique to improve the performance of cellular mobile systems. This paper presents an overview of smart antennas in terms of key characteristics, options, challenges and benefits, in the context of current, but also with a view towards future, generation personal communication systems     

Reflector plasma array antennas

A reflector plasma array antenna is investigated. A plasma array with a controlled pattern is created with the help of a discharge creeping over a dielectric surface. The scattering microwave radiation pattern is calculated for the vertical and horizontal polarizations of the radiation incident on the plasma array.     

Printed antennas for dual-band GSM/DCS 1800 mobile handsets

The recent developments of dual-band dual-mode D-AMPS/AMPS mobile handsets and radiostations has increased pressure on GSM service providers to follow similar technology breakthroughs as a first step towards IMT2000. A frequency-agile device accommodating both GSM standard frequency bands would serve more than 25 million GSM subscribers, with expectations as high as 100 million subscribers by the year 2000. Novel dual-band printed bow-tie antenna elements developed for dual-mode GSM/DCS 1800 handsets are described     

Spaced directive antennas for mobile communications by the Fouriertransform method

The Fourier relations between the channel transfer function and scattering distribution can apply to personal and mobile communications where multipath is a prevalent phenomena. In this paper, the transform relations are reviewed and interpreted for the mobile radio channel. The effective scattering distribution is the vector product of the antenna pattern and the incident waves and is a scalar function of angle and delay time. The space base-band frequency correlation function transforms with the averaged power of the effective scattering distribution. If the angular power density marginal of the effective scattering distribution is known, then the transform relations can be used for configuring antennas for spatial diversity. Similarly, if the delay time marginal is known, then conditions for frequency diversity are available. The two-dimensional (2-D) transform gives a convenient route for assessing tradeoffs between combined frequency and space diversity. Using modeled distributions, solutions are given for spaced directive antennas and an example is discussed for the space-frequency tradeoff     

A bandwidth enhancement technique for mobile handset antennas using wavetraps

A novel technique for enhancing the impedance bandwidth of wireless terminal antennas is presented. By introducing resonant short circuit transmission lines to the long sides of the chassis edges, an effective electrical shortening of the terminal ground plane is achieved. This effect has been used to realize terminal ground planes with resonant lengths at high frequencies, such as GSM 1800/1900 MHz or UMTS 2 GHz, thereby extending the impedance bandwidth. The proposed technique has been validated by simulations and measurements. Three typical applications are presented where the introduction of wavetraps improves the bandwidth and/or in-band performance.     

Environment effects and system performance characterisation of GPS antennas for mobile terminals

The GPS antenna on mobile terminals suffers from multipath effects owing to reflection, diffraction and scattering of the incident wave in a radio environment. A traditional approach to evaluate the GPS antenna performance in a real multipath environment is therefore insufficient. Presented is a new technique to characterise these environmental effects and the system performance of GPS antennas on mobile terminals.     

Design of small and broad-band internal antennas for IMT-2000mobile handsets

The objective of this paper is to design some small broad-band internal antennas for third-generation International Mobile Telecommunications-2000 (IMT-2000) mobile handsets. By introducing substrates of low dielectric constants and electromagnetically coupling two shorted microstrip patch elements, of either rectangular or semidisc shape, both compactness and broad bandwidth can be achieved. These novel internal antennas for IMT-2000 mobile handsets incorporate only one single probe feed in a driven patch element, white the broad-band feature is obtained by realizing dual-frequency operation. The typical impedance behavior and far-field radiation pattern characteristics of eight different antenna configurations are discussed theoretically and experimentally     

Design concept of antennas for small mobile terminals and the future perspective

With the progress and rapid increase in mobile terminals, the design of antennas for small mobile terminals is acquiring great importance. In view of this situation, the design concept of antenna systems for small mobile terminals and its future perspective are discussed, referring to the trends in modern mobile communications and the demands for the antenna system. The design concept of antenna systems has changed along with the progress of mobile systems. In the conventional design, the conducting material of the equipment case, existing near the antenna element, is included as a part of the radiator in the antenna system, without regard to whether or not it has been considered. In the latest mobile phones, the design concept has been advanced to aim at improving the antenna's performance, and the treatment of the case, etc., has become a part of this. Some particular considerations for the design are to relieve the degradation of the antenna's performance due to the human-body effect, to overcome the SAR problems, and yet to make the size small. Furthermore, it is now time to proceed to the more-advanced concept, in which implementation of adaptive control and software is considered, even in small mobile terminals. Typical trends in modern communications systems are discussed, and the demands of these trends-which are summarized as down-sizing, function, and intelligence-are taken up for future antenna structures. Small-antenna technology and the application of the integration technology to antenna systems are essential for realizing such future structures.     

Approximation techniques for the mutual admittance of slot antennas on metallic cones

The effect of scattering from a sharp tip on mutual admittance is investigated for pairs of circumferential and radial slots on a semi-infinite metallic cone. Mutual coupling measurements as a function frequency and angular separation are presented and compared with numerical calculations. The base of the conical model used in the experimental study was terminated in a spherical cap to minimize scattering from the finite length of the apparatus. The circumferential slot results illustrate interference effects between the direct coupling from slot-to-slot via the geodesic path over the conical surface and the tip back scattering. For the radial slot configuration, the results exhibit negligible tip scattering effects. The analysis utilizes a computer calculation of mutual coupling between circumferential and axial slots on an equivalent cylinder to predict the direct coupling contribution and utilizes the tip diffraction coefficient for calculating the component scattered by the apex. The tip diffraction coefficient is derived from an asymptotic expression for the tip-scattered component of the surface magnetic field excited on a semi-infinite conical surface.     

The antennas on a mobile board and their electromagnetic compatibility

This paper presents the solutions of a problem of optimization in the decrease of antenna-coupling coefficients on a mobile board in case of limitations on coverage for each antenna. To determine a minimum value of an antenna-coupling coefficient for one pair of antennas, we use the Gauss-Zeidel optimization method or search method. When two or several antenna pairs have a common antenna, the coordinates of this antenna are determined by the compromise. The algorithms of optimum antenna placement are supported by the computer software and are tested for a case of four antennas.     

Outage probability in mobile telephony with directive antennas and macrodiversity

Signal-to-interference ratio statistics for mobile telephony systems with hexagonal coverage areas, multiple interferers, and three-corner base stations are investigated. Corner base stations simultaneously reduce total interference (because of antenna directivity) and provide macrodiversity against shadow fading. Our results indicate that for 3 or 7 channel sets, with 2 tiers of interferers and typical system parameters (propagation exponent of 3.7 and lognormal spread of 8 dB), the improvement is on the order of 11 dB over a baseline arrangement which employs centrally located omnibase stations without macrodiversity. Additional considerations of blocking probabilities and average voice activity indicate possible further improvements.     

Teletraffic capacity of CDMA cellular mobile networks and adaptive antennas

The teletraffic capacity of a CDMA mobile network with adaptive antennas at the receiver base station is considered and a simplified expression for the system outage probability associated with the teletraffic capacity is obtained. Analytical as well as numerical results show that the outage probability, and consequently the teletraffic capacity of the system, is improved using adaptive antennas at the receiver base station. Copyright © 2002 John Wiley & Sons, Ltd.