Showing papers on "Reflective array antenna published in 1998"

Microstrip antennas for SAR applications

Abstract: This paper discusses various methods of implementing a shared-aperture dual-frequency dual-polarized array antenna for spaced-based synthetic aperture radar (SAR) applications. After evaluating the use of several potential array architecture concepts and radiating elements, a design using interlaced C-band microstrip patches and X-band printed slot elements was chosen as the best choice for the present system requirements. Layout considerations for the two arrays and their associated feed networks are addressed in terms of a practical design. A dual-frequency (C- and X-band), dual-linear polarized SAR array antenna prototype was designed, fabricated, and tested. The principal goal of this effort was to demonstrate the viability of the dual-band dual-polarized array concept, and this has been accomplished. Test results are shown with good correlation between measured and predicted results, validating the design approach used. This work demonstrates that a dual-frequency dual-polarization SAR antenna within a single aperture is a feasible approach to meeting user requirements in future SAR spacecraft.

Microwave phase conjugation using antenna arrays

Abstract: A technique has been developed and tested for achieving phase conjugation in the microwave and millimeter-wave regime. The effective nonlinearity required for this phase-conjugation process is provided by electronic mixing elements feeding an array of antennas. Using these balanced mixing circuits in conjunction with a one-dimensional array antenna, we have demonstrated two-dimensional free-space phase conjugation at 10.24 GHz. A critical factor of this technique is the delivery of a 2/spl omega/ pump signal to each array element with the same phase. Two types of interconnects, electrical and a more versatile optical technique, have been implemented to distribute the pump signal in our demonstrations. In both systems, two-dimensional free-space phase conjugation was observed and verified by directly measuring the electric-field amplitude and phase distribution under various conditions. The electric-field wave-fronts exhibited retro-directivity and the auto-correction characteristics of phase conjugation. Furthermore, these experiments have shown amplified conjugate-wave power up to ten times of that of the incoming wave. This amplifying ability demonstrates the potential of such arrays to be used in novel communications applications.

1 GHz programmable analog phase shifter for adaptive antennas

Abstract: This paper describes a programmable analog phase shifter operating at 1 GHz. This has application in adaptive antenna systems, where variable phase shifters are used to steer the directivity of the antenna array. The circuit is fabricated in 0.8 /spl mu/m silicon bipolar technology, with a 10 GHz f/sub T/. The resulting chip area is small enough to allow 16 complete phase shifter circuits to be included in a single package, thereby allowing control of an array of 16 antenna elements. This approach in constructing adaptive antenna is highly inexpensive compared to the use of bulk microwave phase shifters.

Performance of lens antennas in wireless indoor millimeter wave applications

Abstract: Dielectric lens antennas can be designed to produce highly shaped beams that significantly improve the performance of emerging wireless indoor millimeter wave systems. A lens configuration is analyzed in this paper that produces a circular symmetric cell with uniform spatial distribution of power, with fairly sharp boundaries and scalable cell radius. The last characteristic is used to control the reflections at side walls. An hemispherical coverage lens antenna is designed for the mobile terminal to ensure relatively free movement. The impact of these antennas is analyzed in terms of cell coverage and channel time dispersion, considering the effect of cell radius scaling, and mobile terminal antenna tilting. Measurements and simulations show that the proposed lenses outperform common solutions based on pyramidal horns or biconics.

Receive mode of optical signal processing multibeam array antennas

Abstract: A receive mode of the optical processing array antennas is presented. In this receive mode, the transmitting radio frequency (RF) signals generated by optical processor will be shifted as local oscillator (LO) signals, and the received RF beams will be discriminated in the downconverted intermediate frequency (IF) frequency domain by a mixer array between the optical processor and antenna elements. A proof-of-concept experiment for a two-beam and four-element array antenna is demonstrated, and the received IF power distributions for each beam have very good agreement with the calculated antenna patterns.

Virtual array synthesis method for planar array antennas

Abstract: 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.

Impact of shaped lens antennas on MBS systems

Abstract: Highly shaped beam lens antennas were adopted on the ACTS SAMBA mobile broadband system trial platform to favor high transmission bit rates with moderate RF power requirement and moderate equalization effort. The description of the antenna system and its radiation characteristics are given together with the analysis of the implications of these antennas on the cell coverage and channel time dispersion.

Narrowbeam cylindrical antenna array with sparse antenna spacing

Abstract: We suggest a cylindrical array, which utilizes signal cancellation and sparse element spacing. The array has narrow beamwidth and low sidelobe level. The beamwidth is about 12/spl deg/ for a 35 element array having a -20 dB sidelobe level. An omnidirectional coverage area is obtained by a combination of commutation and phasing. The array has less elements and smaller size than a respective array consisting of linear panels.

A dual-polarized microstrip antenna array with high isolation fed by coplanar network

Abstract: In this paper, serial corner feeding of a square patch with two ports is proposed to realize dual polarization. For the four-element dual-polarized array, a novel coplanar feedline network is presented. An efficient method of analysis is developed and a practical array is manufactured. The measured isolation is less than -40 dB at 6.07 GHz. The proposed array occupies a smaller area than other dual-polarized arrays commonly used and is easier to further combine to form a larger coplanar array.

Spatio-temporal coding for radar array processing

Abstract: The aim of this paper is to present a new method allowing radar digital beamforming (DBF) with only one receiver channel. The key point is the use of a particular spatio-temporal waveform transmitted by an active phased array antenna. By properly choosing the temporal modulation applied on each of the transmission elements, one can transmit different signals in different directions, allowing (under certain hypotheses) angular localisation with only one receiver channel. The major advantage is the design of a low cost system providing DBF capabilities.

System of concentric microwave antennas

Abstract: A system with two concentric antennas for two bands of microwave frequencies includes between the two concentric antennas a system for eliminating or attenuating propagation of waves from the inner antenna to the outer antenna.

Grid array antenna with c-figured elements

Abstract: It is known that a grid array antenna radiates a linearly polarized wave. This paper presents the radiation characteristics of the grid array antenna with c-figured elements. Calculations show that the radiation field is circularly polarized. The frequency responses of the gain and axial ratio in the broadside direction are evaluated. A comparison between the radiation characteristics of the grid array antennas with and without c-figured elements is made and discussed.

A dual-polarized planar array antenna for Ku-band satellite communications

Abstract: The authors propose a low sidelobe dual-polarized planar array antenna for Ku-band satellite communications. In conventional dual-polarized planar array antennas using strip lines and microstrip patch antennas, it is difficult to obtain low sidelobe characteristics because the aperture distribution is deformed from the desired one by electrical coupling between feed lines and element antennas. In the proposed antenna, rectangular coaxial lines have been adopted as feed lines in order to reduce coupling between feed lines. We have developed a dual-polarized element antenna shielded by a cavity, in order to reduce coupling between element antennas and feed lines. Also, we have developed an element antenna arrangement forming the desired aperture distribution by adjusting the number of antenna elements in each row. These developed techniques can achieve sidelobe levels of less than -23 dB which would be lower than those of the conventional dual-polarized planar array antennas.

Compact wide-band microstrip antennas for PCS and cellular phones

Abstract: PCS and cellular telephones are required to operate well beside the human body. Microstrip antennas could be considered as one of the best candidates for such applications. Microstrip antennas are relatively easy to manufacture in a very accurate repeatable way. They may be fed by coupling and thus, there would not be any physical contact between the antenna and the RF circuit. Furthermore, it is relatively easy to separate the receive and the transmit bands of microstrip antennas to eliminate the duplexer or, at least, make it easy to design. Also, it is relatively easy to design dual-band internal integrated microstrip antennas for PCS and cellular telephones. Moreover, internal integrated microstrip antennas may utilize the E and H field component diversity technique which does not require an additional separate diversity antenna.

Conformal array antenna for LEO observation platforms

Abstract: Current X-band links from LEO satellites to ground stations are limited in data rates because of their low gain, due to the global coverage by a single beam. In order to increase the data rate while keeping low DC consumption (so low transmitted power) and to enable simultaneous links with several ground stations, a multibeam scanning antenna was designed and a demonstrator (up to three beams in three adjacent sub-bands) manufactured for an observation mission at an altitude around 800 km. A conformal array was selected by Alcatel, in agreement with ESA, as the best option for such a mission, because of its higher gain compared to a passive fixed beam and its capability of electronic scanning which avoids any mechanical disturbances.

A 64 element broad band volumetric array antenna

Abstract: We present experimental results obtained from a 64 element volumetric array designed for broad band frequency operation. The experimental volumetric array consists of 64 elements arranged in spherical volume of radius 200 mm. Each element is a 7 segment log periodic dipole array designed to provide wide band operation over the frequency range of 6 GHz to 16 GHz. The elements are fed via semi-rigid coaxial cable supported in a stainless steel tubing for extra rigidity. The current array is configured to provide optimum scan performance in the H-plane as, in this orientation, the coaxial feeds are orthogonal to the radiated E-field. At present the 64 element volumetric array demonstrator has no beam forming network and therefore the array scan performance can not be measured directly. However, the main beam characteristics may be synthesised from a knowledge of the measured embedded element patterns. This approach allows accurate predictions of the array performance that include the effects of inter-element coupling.

An array of coupled nonradiative dielectric waveguide radiators

Abstract: A novel antenna array that radiates a single mode of multiple coupled nonradiative dielectric (NRD) waveguides, is described. The array is fed by a single NRD waveguide, which is designed to propagate a wave with the same wave number as that of free-space. The individual radiators of the array are spaced at one free-space wavelength, but due to the narrow beamwidth of the individual radiators, grating lobes are effectively suppressed. An eight-element array is described and measurements presented, but the design method can be extended to any number of elements.

Spatial power-combining using CPW-fed bowtie antennas

Abstract: A new quasi-optical power-combiner geometry consisting of an array of bowtie antennas fed by coplanar waveguide is presented. The bowtie structure provides space to accommodate planar tuning structures as well as multiple devices. An oscillator circuit that includes a heterojunction field-effect transistor (HFET) and coplanar resonator is embedded in one arm of each antenna. Experimental results for a 4/spl times/4 array are provided and an equivalent circuit model used for the array design is described.

Planar near-field measurement of low directivity embedded antennas using a synthetic array probe technique

Abstract: One of the limitations of planar near-field measurement using conventional processing is the inability to test small antennas with typically less than two wavelengths aperture dimensions because of the excessive ripple errors. This ripple is caused by discontinuity of the measured field at the edge of the plane of measurement which causes the generation of equivalent line sources which produce their own radiation pattern after transformation into the far-field. The ripple can also be viewed as resulting from a spectral domain convolution of the scan window and the antenna aperture field which contains a singularity. The technique presented here reduces the near-field level at the edges of plane of measurement by combining near-field data points to form a directive synthetic array of probes. This allows using the planar measurements for measuring antennas embedded in a large structure without rotating these structures or collecting excessively large scan data points. The deconvolution of the array factor in the spectral domain will be independent from the probe correction. The disadvantage of this processing is the limited measurement angular range in which the processed data are valid.

A switchable four-sector shaped-beam antenna for MM-wave wireless LANs

Abstract: The paper presents a four-sector shaped-beam antenna suitable for base station (BS) antennas in the 60 GHz band. This antenna has a plateau configuration whose four side walls have four linearly arranged patch array antenna, respectively. Each trapezoidal facet consisting of four linearly arranged patch array antennas excites a shaped beam in the elevation plane in order to cover from a small depression angle to the nadir, considering the radiation pattern of the developed remote terminal antennas. In order to suppress unwanted multipath delayed waves, they excite right-handed circularly polarised waves.

Dielectric-loaded slotted-cylinder antennas offering reduced base station interference for personal communication services

Abstract: This paper proposes dielectric loaded slotted-cylinder antennas (DSCA) that have, for PCS, horizontally-polarized omnidirectional radiation patterns to reduce the base station interference These rod-shape array antennas are achieved by modifying a slotted-cylinder antenna (SCA) to include dielectric loading The structure of DSCA and the fundamental characteristics, such as input impedance and radiation pattern of the DSCA array, are shown The reduction in the base station antenna interference level and the radio zone length of the DSCA array are confirmed by measured results on an urban street

Conformal Microstrip Antenna Array with Hemispherical Coverage for Mobile Users of Future Satellite Systems

Abstract: Future satellite systems like GNSS-2 for combined communication and navigation services need small and low-cost ground segment antennas with a coverage of more than a hemisphere for mobile users. A candidate for this application is the antenna presented in this paper. It consists of a semi-spherical microstrip patch array for C-band with local planar elements. Beam switching by single element switching avoids the use of complex phased array concepts. The necessary gain is achieved by the use of high gain microstrip patch elements applying superstrate technology. 90°-hybrid-power-dividers in combination with dual linear polarized elements enable the reception and transmission of circularly polarized waves.

Field Profile Synthesis with an Antenna Array

Abstract: Two algorithms for the synthesis of a microwave beam with desired characteristics are discussed. The beam is composed by an array of either identical or non-identical antennas. In an example, the application of those algorithms for wireless power transmission is demonstrated.

Smart antennas

Abstract: Smart antennas have become an essential paradigm for the enhancement of capacity in cellular communications systems. In 2nd Generation Systems smart antennas were aiming at increasing capacity either by reuse within ceN (Space Division Multiple Access SDMA) or by intercell interference reduction (Spatial Filtering for Interference Reduction SFIR). Later in 3rd Generation UMTS UTRA (Universal Terrestrial Radio Access) smart antenna concepts evolved from pure beamforming techniques merely based on directional information of the radio channel to more general spacetime processing concepts which exploit a variety of available processing gains and sources of diversity. As a natural consequence the adaptive antenna and smart antenna concepts in mobile communication systems have become a hot topic in the Technical Specification Groups for Radio Access at 3GPP (Third Generation Partnership Project) who shall prepare, approve and maintain the 3GPP Technical Specifidations and Technical Reports. In this Special Issue of the European Transactions on Telecommunications journal, ainied at presenting original results in the field of Smart Antennas, contributions are collected, which emerged from a special session of the World Micro-Technologies Congress (Hannover, Germany, 2000) which has been incorporated within EXPO 2000. The presented selection of papers comprises almost all varieties of considering and deploying smart antenna concepts in mobile communication systems both in radio layer 1 and 2. The first three papers explicitely refer to applications ofsmart antennas for UTRA FDD and UTRA TDD. The first paper, by C. Brunner, W. Utschick, and J.A. Nossek, presents an overview of eigenbeamfoning concepts in the uplink and downlink techniques for UTRA FDD; the focal point of the paper is the efficient use of short-term and long-term properties of the radio channel. In the second paper, A. Jarosch and D. Dahlhaus focus on the downlink in UTR4 FDD; simple linear demodulation schemes exploiting the space and time diversity of the mobile radic channel are derived. Smart Antennas for UTRA TDD is the tenor of the paper by M. Haardt, C.F. Mecklenbr8ucker, M. Vollmer, and P. Slanina: here both uplink and downlink techniques are discussed; whereas in the uplink the emphasis is on joint detection techniques and its efficient implementation, br the downlink again the efficient use of short-term and long-term properties of the radio channel is discussed. The next two contributions are devoted to more principal investigations of downlink processing. First, H. Troger, T. Weber, M. Meurer, and P. W. Baier present a performance survey of Joint Transmission, a novel downlink transmission scheme, by exemplary system assessments and comparisons. In the next paper, by H. Boche and M. Schubert, the problem of joint downlink beamforming and power control in wireless communication systems is addressed. The third selection of papers contains two prospective topics of smart antennas in wireless communications. In the first paper, R.S. Thoma, D. Hampicke, A. Richter, and G. Sommerkorn present a new real-time MIMO vector radio channel sounder; the proposed MIMO measurement principle can be exploited to estimate channel properties at both ends of the wireless link simultaneously, and thus, dramatically enhance overall resolution of the multi path parameters. Finally, very promising strategies for radio resource management using smart antenna cellular networks are discussed by C. Hartmann and J. EberspZicher, the focus is on adaptive strategies which combine spatial reuse within the cell with dynamic inter-cell channel allocation. We would like to take this room to thank the Editor-in-Chief of the European Transactions on Telecommunications for the opportunity of publishing this Special Issue, as well as the editorial staff at ETT for their assistance during the preparation of the issue and we are especially indebted to the reviewers for their critical comments and their constructive suggestions. We also wish to express'our sincere appreciation to all the authors of this Issue, whose contributions made tis work an important document of recent theoretical and practical advancement of smart antenna concepts.

The benefits of intelligent antenna arrays in TD-CDMA-a study based on measured channel impulse responses

Abstract: In January 1998, ETSI (European Telecommunications Standards Institute) determined the air interface standard for UMTS (Universal Mobile Telecomunications System). This standard will comprise the component TD-CDMA (time division CDMA). In this paper, the suitability of TD-CDMA for utilizing intelligent antenna arrays at base station receivers and the benefits achievable by such antennas are demonstrated by simulations. Different types of antenna configurations are studied. The directional channel models needed for the simulations are derived from measured channel impulse responses.

Phased array feed for communication satellite antennas

Abstract: Phased array antennas are attractive for geostationary satellites because of their many advantages. This paper provides an analytical study of a single reflector antenna fed by an array feed composed of radially aligned elements. The antenna is compared with other phased array antennas such as a direct radiating array and a dual reflector antenna. Given the same environments for feeds and subreflectors, the comparison shows that a phased-array-fed single reflector antenna is superior to a dual reflector in wide angle beam scan capability. A manufactured array feed is described and measured radiation properties are shown. Secondary radiation patterns of the array fed reflector antenna calculated using measured array feed radiation patterns are presented. The agreement with original prediction proves the feasibility of the phased-array-fed single reflector antenna and the usefulness of radially aligned feed array elements.

Design of a beam-switching active microstrip antenna array

Abstract: An active microstrip antenna array with dual switching beams were developed and demonstrated. The array contained several active antennas and an extra amplifier-embedded coupling (microstrip) line. Two injection-locking signals were used in the design, that is, the free-space mutual coupling between antennas and the injection signal on the coupling line tapped from the first oscillator in the array. By turning on and off the amplifier on the line, these two signals dominated in turn, producing two radiation modes with different main beams. A three-element H-plane array and a two-element E-plane array were designed and measured. Both of the arrays had an out-of-phase radiation mode when the amplifier was turned off, and had an in-phase mode when the amplifier was on. Also, clean frequency spectra and good radiation patterns were measured, which demonstrated the validity of the present design.

Beam-forming network characteristics of spatial optical signal processing array antenna for multibeam reception

Abstract: We have experimentally investigated the basic characteristics of a beam-forming network in a spatial optical signal processing array antenna for multibeam reception. In this experiment, two RF signals, which were simulated multibeam antenna receiving signals from different directions, were separated according to the signal arrival direction in the optical domain. The obtained results generally agreed with calculated values.

Microstrip patch antenna design considerations for airborne and spaceborne applications

Abstract: Using manufacturer quoted and measured parameters of substrates, the temperature effects on the performance of airborne and spaceborne microstrip patch antennas have been studied. Extreme centre-frequency drifts have been observed for antennas made of teflon-glass laminates. It has been shown that the temperature drift can be substantially reduced using quartz-fibre composite materials.

Design of high gain dipole antennas using the genetic algorithm

Abstract: High gain antennas are often employed in communication systems to meet specific coverage requirements. To achieve high gain characteristics, one typically uses an array of radiating elements, e.g., active patch antennas, vertical dipoles, etc. By carefully choosing the excitation of each element, and their spacing, one can obtain certain desired gain characteristics, such as a high and narrow main beam with low sidelobes. The article introduces the concept of high gain dipole antennas that are realized by inserting lumped LC loads along the dipole. Also, in an effort to maximize the efficiency of the antenna, we make the loads entirely lossless.