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     

A frame synchronization method for adaptive array antennas in digital mobile communications

This paper proposes a frame synchronization method for an adaptive array antenna (AAA) used in digital mobile communications. The proposed scheme, which is based on the maximum likelihood estimation (MLE), calculates error signals by subtracting a training sequence convolved with an estimated channel impulse response from the AAA outputs and searches for the timing that minimizes the mean squared errors. Because the proposed scheme can effectively exploit delayed paths of the desired signal, it can improve the synchronization performance on frequency-selective fading channels. Computer simulations show that the proposed scheme can operate properly even in interference-rich fading environments and that it can significantly improve the synchronization performance.     

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 with dielectric fin aperture loading

Planar waveguide array structures in which some form of dielectric matching is introduced, either in the form of a continuous sheet above the array face or dielectric plugs in the apertures, have received considerable attention in the literature. An alternative construction has one central dielectric fin or two edge dielectric fins in each rectangular waveguide aperture. Schaedla [2] has given a theoretical analysis for the first type of phased array but does not quote numerical results. In this paper computed results are compared with experimental measurements for simulated array faces of both types. Some conclusions are given regarding the comparative match-scan performance of fin-loaded, fully loaded, and empty waveguides. These results suggest certain advantages for the fin-loaded array configuration.     

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。     

Downlink adaptive array algorithms for cellular mobile communications

The capacity of wireless downlink communication to mobile receivers in a dense urban environment is limited primarily by co-channel interference. Downlink adaptive arrays can be used to mitigate this limitation by maximizing the power transmitted to desired in-cell mobiles in the reference cell while minimizing power to co-channel mobiles in neighboring cells. This is accomplished by using uplink measurements to estimate downlink covariance matrices and then solving a generalized eigenvalue problem. Several algorithms are proposed to adaptively estimate the optimal solution and are evaluated using a simplified signal model that allows efficient deterministic performance calculations.     

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 compact digital beamforming SMILE array for mobile communications

A compact spatial multiplexing of local elements (SMILE) scheme smart antenna array with adaptive beamforming is presented. Low-noise amplifiers are implemented as switching elements to maintain a low system noise figure and allow fast switching. The switching scheme effectively reduces N RF channels to one, reducing the amount of costly RF hardware by a factor of N. The sampling rate must be higher than the signal bandwidth based on the Nyquist criterion to ensure proper restoration of the original signal. Measured data for destination of arrival estimation, beamforming, and digital data recovery demonstrate the capability and benefits of digital beamforming with this architecture.     

Dual-band circularly polarized equilateral triangular-patch array antenna for mobile satellite communications

The Japan Aerospace Exploration Agency will launch the Engineering Test Satellite VIII (ETS-VIII) in 2006 to support the next generation of mobile satellite communications covering the area of Japan (beam coverage El=38/spl deg/ to 58/spl deg/). In this paper, a satellite-tracking left-handed circularly polarized triangular-patch array antenna is developed for ground applications. The targeted minimum gain of the antenna is set to 5 dBic at the central elevation angle (El=48/spl deg/), in the Tokyo area, for applications using data transfer of around a hundred kbps. The antenna is composed of three equilateral triangular patches for both reception and transmission units operating at 2.50 and 2.65 GHz frequency bands, respectively. The antenna was simulated by method of moments (MoM) analysis, and measurement of the fabricated antenna was performed to confirm the simulation results. The measurement results show that the frequency characteristics and the 5-dBic gain coverage in the conical-cut plane of the fabricated antenna satisfy the specifications for ETS-VIII. A prototype of the proposed antenna system is employed in outdoor experiments using a pseudosatellite and shows good performance from El=38/spl deg/ to 58/spl deg/.     

Base-station tracking in mobile communications using a switchedparasitic antenna array

Base-station tracking in mobile communications benefits from a directional antenna and so requires direction finding technology. A novel technique for electronically directing the radiation pattern of an antenna array employs a directional array with only one active element and three parasitic elements operating near resonance. Three different methods of direction finding are assessed; a coarse angular location method, a precise angular location method assuming one incident beam, and a precise angular location method with multiple incident beams. An array with n elements, if used in conjunction with a relatively simple controller, can be used to resolve n-1 signals. This technology can be implemented using both wire and patch antenna-array elements and either linear or circular polarization can be used, lending the technology to applications in both terrestrial and satellite communications systems     

Polygonal patch antennas for wireless communications

An effective design of polygonal patch antennas with multifrequency or broad-band operation modes for wireless communications is presented in this paper. It is shown how polygonal patches with suitable features may be obtained after a proper perturbation of conventional rectangular geometries, which inherently present poor bandwidth performances. These perturbed irregular geometries may support multiple resonances and, thus, may present a broad-band or multifrequency operation mode, even employing conventional patch antennas with a single dielectric substrate. These polygonal patches are efficiently analyzed through a numerical code based on the method of moments, with entire domain basis functions that accurately describe the radiation mechanism. After the presentation of the analysis and design techniques, some antenna layouts for modern wireless communication systems will be proposed. Such antennas are designed for both universal mobile telecommunication system and wireless local area network portable equipment with real-life finite ground planes.     

Multibeam antennas for indoor wireless communications

A multibeam beamformer in combination with a decision feedback equalizer is considered for the base station in a single-cell 100-Mb/s TDMA/TDD QPSK indoor wireless network at 24 GHz. The outage rate in terms of required SNR/bit/antenna is estimated using a statistical, clustered propagation model and for beam selection diversity and two-beam combining     

Phased array calibration

Calibration of a phased array antenna while the antenna is in service can be a complex and time-consuming procedure that affects use of the antenna and imposes an unacceptable overhead on the system. The procedure described herein uses a maximum likelihood algorithm to minimize the number of measurements, thus reducing the impact on the system and shifting the overhead to a remote site     

Virtual array synthesis method for planar array antennas

A new array antenna synthesis method, which we call the virtual array synthesis method, is presented. In this method, the excitation values of a virtual array are synthesized using some known synthesis method. The geometry of the virtual array can be chosen so that there will be a suitable synthesis method for that geometry and the synthesis of the virtual array can be done accurately enough. In the synthesis method presented, the excitation values of the virtual array are transformed into the excitation values of the actual array geometry. Matrix operations are simple and large arrays can be easily synthesized     

Self-phasing array antennas

A self-phasing array antenna is described which operates on the incident wavefront in such a manner that when it is retransmitted it returns whence it came as a coherent wavefront irrespective of the original phase distribution incident on the array. Self-phasing is useful where a two-way propagation path is available and where a conventional antenna cannot operate efficiently because of an unknown phase distribution in the incident wavefront. The operation of a self-phasing array, its properties, its relation to other antenna design techniques and its potential applications are discussed.     

Wide-band E-shaped patch antennas for wireless communications

This paper presents a novel single-patch wide-band microstrip antenna: the E-shaped patch antenna. Two parallel slots are incorporated into the patch of a microstrip antenna to expand it bandwidth. The wide-band mechanism is explored by investigating the behavior of the currents on the patch. The slot length, width, and position are optimized to achieve a wide bandwidth. The validity of the design concept is demonstrated by two examples with 21.2% and 32.3% bandwidths. Finally, a 30.3% E-shaped patch antenna, resonating at wireless communication frequencies of 1.9 and 2.4 GHz, is designed, fabricated and measured. The radiation pattern and directivity are also presented     

Phased array for millimeter wave frequencies

A phased array is presented at a frequency of 70 GHz, consisting of a corporate feed, ferrite phase shifters and dielectric rod antennas. Metal waveguides were utilized to construct the feed network, whereas a special dielectric waveguide structure was employed for the ferrite phase shifter and dielectric rod antenna. Beam scanning can be performed electronically controlled in the horizontal plane.     

An implementation of a CMA adaptive array for high speed GMSKtransmission in mobile communications

The hardware implementation of an adaptive array as a technique for compensating multipath fading in mobile communications is described. The number of the antenna elements is four. The target communication system is modulated by 256 kbps Gaussian-filtered minimum shift keying (MSK) and has a time-division multiplexing (TDM) architecture with 24 time slots. Based on the digital beamforming concept, all of the signals and the array weights are digital-signal processed. The constant modulus algorithm (CMA) is employed for weight optimizing. In an additive white Gaussian noise channel, this system has 5.6-dB gain in an energy-per-bit-to-noise-density ratio at a bit error rate (BER) of 1.0×10^-3, compared with a single antenna system. The result of the basic field test shows that the gain at a BER of 1.0×10^-3 reaches 22.3 dB in a nonselective, slow Rayleigh fading channel given a 5 Hz maximum Doppler shift     

MSW applications for phased array antennas

A potential application of MSW technology lies in the area of time delay for future low-sidelobe wide-bandwidth phased array antennas. High-precision MSW electronically tunable analog time-delay units in transmit/receive modules in phased arrays have the potential of greatly enhancing antenna system capabilities, by increasing instantaneous operating bandwidth and decreasing sidelobe levels, over phased array systems using only phase shifters or switched lines for beam steering and control. This paper provides a status report of MSW time delays for such arrays.