Showing papers on "Reflective array antenna published in 2002"

On the size requirement for finite phased-array models

Abstract: The question considered is how large an array model must be in order to capture approximately the characteristics of both the interior and the edge elements of a large multi-octave phased array. Arrays with tapered slot elements and with top-loaded dipoles are analyzed at element spacings as small as 0.1/spl lambda/ and it is concluded that at any frequency, a finite array model with this type of element should be at least 5/spl lambda//spl times/5/spl lambda/ in size. This suggests the generalization of the 10/spl times/10 element model often used as an engineering "rule of thumb" in the normal narrow-band case with 0.5/spl lambda/ element spacing. An array model with a 5:1 bandwidth thus needs about 25 times more elements than a narrow-band model. The array feed impedance is considered and it is found that the array active reflection coefficient in finite arrays but not in infinite arrays is dependent on the matching condition at the feed. The finite-difference time-domain (FDTD) technique is used to analyze arrays up to 49/spl times/49 elements, demonstrating that computer power now makes feasible the full wave solution for large phased arrays with complex geometry.

Multiple antenna diversity for wireless LAN applications

Abstract: An antenna system comprising a plurality of antennas designed and oriented to provide one or more of radiation pattern, signal polarization and spatial diversity. The various diversity operational characteristics are achieved by using similar antennas physically oriented to provide the diversity attributes or by using dissimilar antennas, that is, antennas having different radiation pattern and/or signal polarization characteristics.

Fresnel Zone Antennas

Abstract: Acknowledgement. 1: Introduction. 2: Offset Fresnel Zoneplate. 3: Phase Correcting Zoneplates. 4: Zonal Reflectors. 5: Single Printed Flat Reflector. 6: Reflective Array Antenna. 7: Other Fresnel Zone Antennas. Bibliography. Index.

Radiation patterns and correlation of closely spaced linear antennas

Abstract: A simple point source analysis is used to prove that, in theory, completely decorrelated reception can be achieved from two linear antennas with an arbitrarily small spacing. The conditions necessary to achieve this are consistent with two high gain (superdirective) beams in opposite directions. It is shown that the horizontal radiation patterns and correlation coefficient of arrays of vertically orientated linear antennas can be found via an exact relation to simple, point-source theory that includes the effects of mutual coupling. This theory leads to practically achievable optimum diversity designs at closer spacings than previously thought possible. The theory is illustrated for a dual antenna configuration and can be extended to multiple antennas.

Array antennas for JPL/NASA Deep Space Network

Abstract: Recently, JPL has begun an assessment of the long-term capability of the antennas for the Deep Space Network (DSN). Various alternative plans for upgrading or replacing the present 70-meter antennas have been considered. Several options have been studied which include modifying the present antennas for extended life and reliability, new 70-meter single aperture antennas with offset or symmetric feeds, 100-meter spherical antennas, an array of a few smaller 34-meter antennas, a much larger array (hundreds) of much smaller (5-10 meter) reflector antennas, and finally active planar phased arrays with millions of elements. In this paper we briefly discuss various options but focus on the feasibility of the phased arrays as a viable option for this application. Of particular concern and consideration will be the cost, reliability, and performance compared to the present 70-meter antenna system. Many alternative phased arrays including planar horizontal arrays, hybrid mechanically/electronically steered arrays, phased array of mechanically steered reflectors, multi-faceted planar arrays, phased array-fed lens antennas, and planar reflect-arrays are compared and their viability is assessed.

Combined open and closed loop beam forming in a multiple array radio communication system

Abstract: A method and apparatus are provided that can combine the benefits of beamforming with transmit diversity. In one embodiment, the invention includes sampling a signal received from a remote radio at elements of an antenna array, deriving spatial parameters for transmitting a signal to the remote radio from an antenna array, sampling the signal received from the remote radio at elements of at least one additional antenna array, and deriving spatial parameters for transmitting a signal to the remote radio from the at least one additional antenna array. The invention further includes generating diversity parameters for transmitting a signal to the remote radio using each antenna array as an element of a diversity array, and transmitting a signal to the remote radio using the spatial parameters and the diversity parameters.

Low-loss tuning circuits for frequency-tunable small resonant antennas

Abstract: Minimization of power loss in the tuning circuits of frequency-tunable small resonant antennas, such as microstrip patches, is studied. First, the frequency shift and the associated power loss in certain tuning circuits are theoretically calculated based on approximate circuit models of fairly narrowband resonant antennas. By investigating the ratio of frequency shift and loss, an optimal configuration for the tuning circuit can be determined. The theoretical results can be used to provide optimal starting values and design curves that facilitate the final design with a full-wave electromagnetic simulator. To support the theory, a design procedure is demonstrated with two example antenna structures, for which both simulated and measured results are presented.

Shorted spiral-like printed antennas

Abstract: We present two electrically small printed antennas suitable for mobile communication handset terminals. The conductor shapes of the proposed shorted patch antennas maximize the length of the current path for a given area thereby significantly reducing the resonant frequency of the antenna. Reductions in operating frequencies of the order of seven to ten have been achieved.

Mutual coupling between cylindrical probe-fed dielectric resonator antennas

Abstract: The mutual coupling between two cylindrical probe-fed dielectric resonator antennas was measured in both the E- and H-planes for varying separations. The resulting measurements were shown to verify existing theoretical predictions and indicate the applicability of these types of antennas for array applications.

Wide bandwidth flat panel antenna array

Abstract: A cavity-backed wideband slimline flat panel antenna array for providing a steerable beam includes an array of slot antennas, each of which fed by its own individual dipole radiator, with the wide bandwidth being due to the matching impedances of the slot antenna and dipole radiator across the entire frequency band. In one embodiment, an upstanding printed circuit balun feed is connected to each dipole. The dipole elements are located to either side of a slot, and are arrayed on the underneath side of a dielectric layer under the substrate into which the slots are formed, with the dipole elements directly fed by individual upstanding printed circuit baluns which are arrayed beneath the individual slots antennas. The use of the dipole elements, in addition to providing a wider operational bandwidth, also permits feeding each of the slots without having to use striplines which would have to cross each other and therefore not work. A wide bandwidth steerable flat panel array utilizing the dipole fed slot antennas may be mounted on the deck house or other flat structural component of a vessel so as to perform a “smart skin” function in which the antenna not only functions as a radiating element, but also as a structural part of the vessel itself. In commercial applications, the flat panel array may be incorporated into the wall of a building such that point-to-point communications between buildings may be accomplished through an antenna which is also a structural part of the building. Note that the beams from the antenna are aimable by appropriately phasing the array to point at a receiving antenna on an adjacent building.

Conformal array antenna for observation platforms in low Earth orbit

Abstract: A conformal array antenna can provide the flexibility that platforms in low Earth orbit need to download their data to ground stations. It does this by producing multiple beams for various ground stations. Even if only one ground station is used at a time, the higher gain of this antenna, compared to a fixed-beam antenna, allows the ground-station antennas to be down-sized, or, equivalently, the data rate to be increased. Moreover, missions on which disturbances in the platform attitude are critical can take advantage of a phased array with no moving parts. Although the demonstration model was targeted at a low-Earth-orbit mission, the concept is equally applicable to future interplanetary science missions.

Impedance matching technique for microwave folded slot antennas

Abstract: Coplanar-Waveguide (CPW) fed Foldcd Slot Antennas (FSA) are becoming important in microwave and millimeter-wave applications with the increased popularity of coplanar waveguide (CPW) transmission lines. They are low-profile, conformal, light in weight, simple to build, can easily be integrated with active devices and had been found to provide large bandwidths. As mentioned in [I] , these characteristics make FSAs attractive for active arrays. Figure 1 shows a sketch of a FSA and its design parameters.

Fractal antenna with RF MEMS switches for multiple frequency applications

Abstract: A new concept of combining RF MEMS switches with fractal antennas is presented. The idea is to connect several antenna configurations together using RF MEMS switches to cover several frequency bands. By using a 'smart combination' of fractal shaped antennas, wideband coverage can be achieved for satellite and wireless communications. Moreover, the same antennas can be used for phased array applications as well. The analysis and design principles are discussed and presented. Several examples are shown to demonstrate the proposed concept.

Smart antenna array

Abstract: The present invention relates to a beamforming method for smart antenna arrays. Smart antennas employ arrays of low gain antennas connected to a combining/beamforming network. Smart antennas can provide enhanced coverage through range extension, hole filling and improved building penetration. By improving transmission and reception at the base station, the tolerable path losses can be increased whereby the range of the base station can be improved. A first aspect of the invention addresses the feedback signalling technique presently being considered by standards bodies for four antennas in large arrays. The invention is suitable for CDMA wireless cellular systems, as presently determined for third generation cellular wireless networks, and other wireless systems such as TDMA systems and wireless LANs.

Four element array of cassegrain reflect or antennas

Abstract: A multi-reflector antenna array capable of simultaneously transmitting and receiving communication signals at Ku-band frequencies is mounted on an exterior surface of an aircraft. The antenna array provides four cassegrain reflector antennas mechanically connected together in a group capable of being simultaneously mechanically scanned. A common support structure fixes the antennas with respect to each other. A drive mechanism and directional azimuth and elevation motors control the position of the array. The aerodynamic drag of the array is minimized using four antennas rather than a single large diameter antenna. Each antenna is positioned on a common horizontal centerline. Two centrally located antennas are positioned between two smaller diameter antennas. The antennas and positioning equipment are both mounted for rotation within a radome. A corporate power combiner/divider is provided to adjust both an amplitude and a phase of each antenna signal.

A flat four-beam compact phased array antenna

Abstract: This paper presents a flat four-beam compact phased array antenna. The low-cost and compact phased array antenna is designed using a circular array of four circular microstrip antennas made of low-cost material and four 1-bit phase shifters. The main beam of the antenna can be switched in four directions with the gain of about 4 dBi in each main-beam direction. More than 90/spl deg/ half-power beamwidth and over 10 dB F/B ratio are obtained. In addition, the diversity performance is considered and the diversity performance of this antenna can be provided with the envelope correlation about 0.6.

Colocated antenna arrays: design desiderata for wireless communications

Abstract: We report on in this paper is motivated by the drive towards antenna array miniaturization: going from an array of identical antennas that get spread out in space towards an array of colocalized antennas with differing responses. We address the problem of designing the colocated antenna array response for two applications: diversity reception using maximum ratio combining and MIMO communication capacity. The design criteria are derived under specific models regarding the distribution of the parameters of the frequency flat channel. We are particularly interested in evaluating the performance of two opposite extremes in terms of design: very selective beamspace type of operation versus spatially allpass antennas. We also show that the pathwise channel model converges for large number of paths to the stochastic channel model with separable correlation between TX and RX sides.

Multi-band characteristics and fractal dimension of dipole antennas with Koch curve geometry

Abstract: Fractal geometries have been studied for antennas with special characteristics, both as antenna elements, and as spatial distribution functions for elements in antenna arrays Koch dipole and monopole antennas have been studied recently as smaller sized antennas, and their multi-band characteristics have been reported (see Cohen, N, IEEE Professional Program Proc of Electronics Industries Forum of New England, p43-9, 1997; Puente-Baliarda, C, IEEE Trans Antennas Propagat, vol48, p1773-81, 2000) We try to establish a link between the interval of multi-band characteristics of dipole Koch curve antennas with the dimension of the underlying fractal geometry

A hexagonal adaptive antenna array concept for wireless communication applications

Abstract: The paper describes an adaptive antenna array concept with seven patch elements in a hexagonal arrangement. With this structure, it is possible to configure the radiation pattern to obtain directional patterns with high directivity and gain. The software IE3D, from ZELAND, was used to optimize and analyze the antenna array for applications at 1.9 GHz. The return loss results and radiation pattern simulations indicate that this hexagonal array can be applied to the next generation of wireless communication.

Design and measurement of conformal antennas

Abstract: An increasing number of complex and dedicated antennas in automotive systems, mobile communication and spaceborne and airborne applications require conformal integration. The term conformal antennas stands for antennas which are confined to the surface of the mechanical carrier. In addition to aerodynamical, aesthetic or integration features, conformal antennas can provide special antenna pattern requirement by an appropriate geometrical form. This contribution discusses the advantages and drawbacks of cylindrical and spherical microstrip array antennas in terms of electrical performance and mechanical setup. It further outlines the design of these antennas and shows measured results for aperture coupled microstrip patch arrays on cylindrical and spherical surfaces.

Application of phased-array antenna technology to the 21 GHz broadcasting satellite for rain-attenuation compensation

Abstract: The signal attenuation due to rain is greater in the 21 GHz band than in lower bands and this is one of the major factors limiting the availability of services in this band. A broadcasting satellite system is proposed in which phased-array antenna technology is applied to overcome the effect of rain-attenuation. Concentrated radiation beams created by a phased-array antenna cover areas of heavy rain, and the same antenna covers other areas with a spread radiation beam. We discuss the outline of this 21 GHz broadcasting satellite system and examine the major hardware elements, such as the array-fed reflector and a TWT suitable for an array configuration.

Technical issues associated with the detection of buried land mines with high-frequency seismic waves

Abstract: An array of radars is developed as a stand off sensor for use in elastic/seismic mine detection systems. The array consists of N radar sensors which operate independently to sense the displacement of the surface of the earth due to elastic waves propagating in the earth. Each of the sensors consists of a lens-focused, conical, corrugated, horn antenna and a homodyne radar. The focused antenna allows the sensor to have greater standoff than with the previous unfocused antenna while maintaining the spatial resolution required for a mine detection system. By using an array of N sensors instead of a single sensor, the scan rate of the array is improved by a factor of N. A theoretical model for the focused antenna is developed and an array of two radars is developed and used to validate the theoretical model. This array is tested in both the experimental and the field models for the elastic mine detection system. Results from both systems are presented.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Modeling of slow-wave EBG structure for printed-bowtie antenna array

Abstract: The novel printed antenna array consisting of series-fed bowtie radiators, finite-width conductor-backed coplanar waveguide-to-coplanar stripline (FW-CBCPW-to-CPS) transitions, and slow-wave electromagnetic bandgap (EBG) structure is presented. By controlling the size and the cascaded number of EBG cell, this structure appears as a slow-wave transmission line that can exhibit large phase shift with broad bandwidth for antenna array applications. The equivalent circuit is also established to model the phase shift of EBG cell. Measured results show that the antenna array achieves a 50% frequency bandwidth for 10-dB return-loss criterion and an end-fire radiation pattern with a front-to-back ratio greater than 20 dB. Good agreement among measured, full-wave simulated, and calculated results supports the validity of the phase-shifting model of EBG structure to predict the main beam angle of the antenna array. Compared to the conventional solid-state phase shifters for antenna arrays, the proposed slow-wave EBG structure has the advantages of higher compactness and lower cost and it is easier to integrate in the FW-CBCPW-fed bowtie antenna array with broad-band and end-fire radiation characteristics.

Signal correlations in coupled cell and MIMO antennas

Abstract: Introduction Keeping signal correlation low across antennas is critical for good receive diversity in cell communications, and for creating independent transmission channels in high data rate MIMO (multiple-input multiple-output) techniques. Tools to achieve this are particularly important when trying to pack multiple antennas into small mobile terminals. Analyses of signal correlations for these applications usually neglect mutual antenna coupling. This paper presents precise formulas for the correlation between signals in mutually coupled antennas, for both 2D and 3D diffusive propagation environments. New values of optimal antenna spacing are given, and closely spaced antennas are predicted to work much better than previously expected.

Re-configurable array antennas for wideband applications

Abstract: A new approach to wideband re-configurable antennas using RF MEMS switches is presented here Several antenna configurations can be connected together using RF MEMS switches The goal is to cover several frequency bands by using a "smart combination" of antennas, including fractal antennas The analysis and design principles are discussed and presented in here

Parallel fed collinear dipole array antenna

Abstract: A parallel fed colinear dipole array antenna for broadcasting and receiving a signal of a selected wavelength The antenna comprises a plurality of elongate dipole antennas attached end-to-end in a linear array A power divider divides and transmits a signal in parallel to each of the dipole antennas The linear spacing of the dipoles is correlated with the dimensions of the dipoles and the selected wavelength, such that the signals of the dipole antennas interfere with each other when broadcast, so as to focus signals which propagate substantially perpendicularly to the linear array, and to diminish other signals

A retrodirective antenna array using a spatially fed local oscillator

Abstract: This work investigates a spatially fed local oscillator (LO) for a retrodirective antenna array. Compared to conventional planar transmission-line feed networks, the spatial feed offers a more flexible array layout and easier implementation, especially in large two-dimensional (2-D) arrays. This method of delivery involves radiating the LO through free space to the back-side of the array where it is received by slot-coupled patch antennas and delivered to the mixing elements. A four-element linear retrodirective array utilizing this approach is demonstrated at an LO frequency of 10.7 GHz. Retrodirectivity is observed at scan angles from -40/spl deg/ to +40/spl deg/.

Intruder/escapee detection system

Abstract: A detection system for detecting intruders moving in the vicinity of a defined path comprises a distributed antenna, for example an open transmission line, extending along the path, and an array of discrete antennas extending alongside the distributed antenna and within a predetermined distance therefrom. The discrete antennas and the distributed antenna define a plurality of detection zones. A radio frequency transmitter is connected to each of the discrete antennas, and a complementary receiver in a control unit at a remote location is connected to the distributed antenna. The control unit also controls the transmitters, and the array of antennas to exchange radio frequency energy between the distributed antenna and the discrete antennas and analyzes the energy received from the discrete antennas so as to detect perturbations caused by an intruder moving adjacent said path and adjacent a particular antenna. A plurality of cameras are associated with the plurality of discrete antennas, and coupled to the control means for transmission of video signals thereto. The control means selects for display a signal from a particular camera in dependence upon the detection of a perturbation from an adjacent discrete antenna.

Method of controlling transmission in a radio system

Abstract: The invention relates to a method of controlling a radio system in a base transceiver station (204), in which base transceiver station (204) at least one antenna array is formed, which comprises at least two antennas (236, 238) for transmitting and receiving a signal, and in which method at least two antennas (236, 238) of each antenna array are arranged in such a way that antenna beams (410, 412) formed by the at least two antennas deviate vertically from each other what it comes to at least one property thereof. The antenna array can be controlled in a desired manner by controlling the ratio of the signal powers supplied to each antenna of the antenna array. The solution of the invention provides for instance flexibility for controlling signal power, which reduces interference in a radio system and increases data transmission capacity in a radio system.

Rolled edge ultra-wideband dipole antenna for GPR application

Abstract: The ever-increasing interest in ground penetrating radar (GPR) for local high resolution interrogation of buried objects or environments has made an impact on the design of ultrawideband (UWB) antennas. Antenna requirements have been stimulated by applications including; utility location, building construction inspection and foreign object detection e.g. archaeological survey or as intended here buried land mine imaging. The strength of signal returns from low dielectric contrast discontinuities tends to be weak, typically less than a few percent of the r.m.s. power transmitted. An obvious solution is to place the receiving antenna in close proximity’ with the air ground interface [I]. More fundamentally, the overall radar system performance places emphasis on two key aspects of antenna design; the efficient transfer of electromagnetic energy (implying low losses) and reducing the level of “clutter” signals originating within the antenna.