Showing papers on "Reflective array antenna published in 2007"

Electronically Scanned Arrays

Abstract: Scanning arrays present the radar or communications engineer with the ultimate in antenna flexibility. They also present a multitude of new opportunities and new challenges that need to be addressed. In order to describe the needs for scanned array development, this book begins with a brief discussion of the history that led to present array antennas. This text is a compact but comprehensive treatment of the scanned array, from the underlying basis for array pattern behavior to the engineering choices leading to successful design. The book describes the scanned array in terms of radiation from apertures and wire antennas and introduces the effects resulting directly from scanning, including beam broadening, impedance mismatch and gain reduction and pattern squint and those effects of array periodicity including grating and quantization lobes and array blindness. The text also presents the engineering tools for improving pattern control and array efficiency including lattice selection, subarrray technology and pattern synthesis. Equations and figurers quantify the phenomena being described and provide the reader with the tools to tradeoff various performance features. The discussions proceed beyond the introductory material and to the state of the art in modern array design. Contents: Basic Principles and Applications of Array Antennas / Element Coupling Effects in Array Antennas / Array Pattern Synthesis / Subarray Techniques for Limited Field of View and Wide Band Applications

Increasing Channel Capacity of an Ultrawideband MIMO System Using Vector Antennas

Abstract: Recently it was shown that co-located vector antennas can provide the same capacity increase as spatial array antennas in multiple-input multiple-output (MIMO) systems. This paper describes the design of a vector antenna consisting of a loop antenna and two orthogonal bowtie antennas for a ultrawideband (UWB) MIMO system that operates in the frequency range 3.6-8.5 GHz. Channel capacity calculations performed with the antenna operating in a rich scattering environment show that spectral efficiency of the UWB vector antenna system approaches that of the traditional spatial array. This demonstrates that vector antennas can be used in place of spatial arrays where compact UWB multiantenna systems are needed.

Indirect Holographic Techniques for Determining Antenna Radiation Characteristics and Imaging Aperture Fields

Abstract: Indirect holographic techniques offer the potential of using simple and inexpensive near-field intensity-pattern measurements for the determination of the radiation characteristics of microwave antennas, and for the reconstruction of complex aperture fields. This work describes a practical method of applying indirect holographic techniques to microwave antennas. It describes how a technique originally developed at optical frequencies can be adapted to enable measurements to be taken on microwave antennas. The major difference is the replacement of a radiated reference signal by an electronically generated reference signal. This has enabled previous practical limitations to be overcome. Computer simulations and practical results are included for a large dish antenna at a sample spacing similar to those employed in direct holographic techniques. This work also describes how reducing the sample spacing significantly below a half wavelength enables the radiation characteristics of smaller antennas to be determined

A Novel Methodology to Feed Phased Array Antennas

Abstract: A new methodology to design beam-forming networks (BFN) to feed antenna arrays is introduced. Using this methodology is feasible to reduce the complexity of the associate control of a phased array, since, an N by N antenna array could be controlled to steer the beam using four phase shifters instead of the N2 conventionally used. A prototype was designed, built and measured as proof of concept. The prototype consists on 3 by 3 Quasi-Yagi antennas fed by four input-ports. The measurements show that the main beam of an antenna array fed by this BFN can be steered to any desired direction.

Vibrating antennas and compensation techniques Research in NATO/RTO/SET 087/RTG 50

Abstract: Array antennas which are integrated onto structures of aircraft and unmanned aerial vehicles (UAVs) are subject to unsteady aerodynamic loads. Mechanical forces and these aerodynamic loads will cause deformation of the antenna supporting structure. As a consequence, the positions and orientations of the elements of the phased array antenna change. The relative phases of the respective signals feeding the antennas will vary, and as a consequence the antenna radiation pattern is affected: the main beam direction can change and the beam width and/or side lobe levels can increase. The influence of deformations and vibrations will be most significant on array antennas, which are large in terms of wavelength (high gain antennas). The objective of the present paper is to present some applications of such array antennas, and to discuss the effects of deformations and vibrations on the performance of array antennas, and to describe technology to counteract these effects by means of adaptive or synthetic beam forming.

Radio communication method, transmitter, and receiver

Abstract: Of the antenna group composed of multiple ones of the transmission antennas and multiple ones of the reception antennas, the present method selects an antenna group which satisfies a first criterion relating to communication quality. Out of combinations of transmission antennas and reception antennas included in the selected antenna group, combinations which satisfy a second criterion relating to communication quality are selected. Using a part of or all of the selected combinations of transmission antennas and reception antennas, the above-mentioned communication is performed. As a result, selection of optimal transmission antennas and reception antennas according to radio communication environment can be performed with high speed with a smaller amount of operation amount than the previous art.

Method for accurate auto-calibration of phased array antennas

Abstract: A method and apparatus is disclosed that is capable of verifying on site the health, calibration and integrity of individual phased array modules of a phased array antenna system and, in certain cases, enabling the phased array antenna system to overcome element failures by use of a beam-steering computer The present disclosure provides a test probe or RF radiator in or adjacent the antenna array for supplying and receiving test and calibration signals

Resolution antenna array using metamaterials

Abstract: An antenna array includes at least one transmit array comprising a plurality of metamaterial elements. The antenna array further includes at least one near-field stimulator for inputting electromagnetic signal to the transmit array so that a sub-wavelength target is illuminated with an electromagnetic wave.

Rfid portal array antenna system

Abstract: This invention provides an array antenna for a radio frequency identification (RFID) system, the array antenna comprises a transmission line with a longitudinal span proximately equaling to a height of a space desired to be covered by the array antenna, the transmission line having a terminal coupled to a RFID reader, and a plurality of radiating elements disposed on the first transmission line along the longitudinal span, additionally, reflective materials used behind the array antenna to maximize the illumination in the desired space and absorptive materials installed surrounding the desired space, in order to minimize the illumination of the undesired space surrounding the desired space.

Planar Beam-Forming Array for Broadband Communication in the 60 GHz Band

Abstract: A planar beam-forming antenna array is proposed that operates in the 60 GHz frequency band. The array consists of 6 balanced-fed aperture-coupled patch antenna elements [2] that are placed in a circular configuration. The resulting array has a maximum gain of 14 dBi and a 3 dB scan range of ±50 degrees. To demonstrate the performance, test arrays have been implemented with accompanying feed networks that apply the appropriate phase distribution over the array for beam-forming at several specific scan angles. Measurements validate the proposed array configuration. (6 pages)

A Compound Printed Air-Fed Array Antenna

Abstract: After a brief review on reflectarray, transmitarray, and Fabry-Perot resonator antennas summarized as a family of printed air-fed array antennas, a novel compound structure is proposed. Its design flowchart is expressed step by step. Some designed samples are described with optimized performance of directivity or frequency bandwidth.

Element Efficiency: A Unifying Concept for Array Antennas

Abstract: The antenna-element efficiency parameter quantifies the effect of mutual coupling in array antennas. In general arrays, this efficiency varies from element to element. The average value of these element efficiencies is a significant summary parameter, and plays a prominent role in circumscribing array performance. A useful formula gives the minimum number of antennas necessary to realize a prescribed peak gain envelope. The important special case of an array of identical elements situated in identical array environments is termed an idempotent array. In particular, an infinite idempotent array models a large planar array. There, the unique element efficiency has been directly related to the rms value of the conventional active reflection coefficient as it varies when the beam is (phased) electronically steered. The element-efficiency formulation also provides a framework for the rigorous derivation of important theoretical results in the theory of phased arrays.

Adaptive antenna apparatus including a plurality sets of partial array antennas having different directivities

Abstract: An adaptive antenna apparatus comprises M receiving circuits, and N antenna elements, N being larger than M. The N antenna elements constitute a plurality of sets of partial array antennas each including M antenna elements among the N antenna elements, and a straight line passing through feeding points of two of the antenna elements included in any one of the partial array antennas has a different direction from a further straight line passing through feeding points of two of the antenna elements included in any one of the other partial array antennas. A control means adaptively controls the receiving circuits to adjust at least one of an amplitude and a phase of each radio frequency signal, and adaptively controls an antenna switching means to connect the antenna elements included in one of the plurality of sets of partial array antennas to their corresponding receiving circuits.

Low-Profile Patch Antennas for Over-Body-Surface Communication at 2.45 GHz

Abstract: Two low-profile patch antennas on small ground planes (0.25 lambda), suitable for over the body surface communication at 2.45 GHz are presented. On-body performance was investigated using FDTD simulations of S21 coupling of shorted microstrip patch antennas (S-MPA) and higher-order mode microstrip patch antennas (HM-MPA) placed on numerical tissue phantoms with characteristics of muscle tissue. The low-profile antenna coupling results are comparable to those achieved using a quarter wave monopole antenna on the same size of groundplane, mounted normal to the tissue surface, indicating that the low-profile antennas studied are promising for bodyworn antenna applications.

Miniaturization of top-loaded monopole antennas using Peano-curves

Abstract: Many wireless applications require planar antennas but with monopole-like, vertically polarized radiation, a design challenge that cannot be easily achieved by using conventional microstrip patch or other types of printed antennas. In addition, while there have been significant advances in design of low-profile printed patch-type antennas in the frequency ranges of L-band and above, the patch antennas are not suitable for lower frequency applications, such as those in VHF and UHF bands, because of their relatively large dimensions. These requirements provide challenging problems in optimization and design of the future generation of low-profile reconfigurable antenna systems. In the present work, we discuss the use of printed metallic paths in the form of Peano and Hilbert space-filling curves (H. Sagan, 1994) to provide top-loading properties that miniaturizes monopole antenna elements. The full-wave simulation together with measured results shows that the proposed electrically small antenna results in a perfect mono-polar radiation pattern with relatively wideband characteristics. Some initial numerical results of this work were recently presented in J. McVay and A. Hoorfar, (2006)

Wideband and Wide Scan Phased Array Microstrip Patch Antennas for Small Platforms

Abstract: The paper presents an overview of research results from FOI on wideband and wide angular coverage, phased array microstrip patch antennas. The research has been motivated by their potential use in future applications in radar, multi- band satellite communication, electronic warfare, and multifunction systems. The paper presents the design and experimental evaluation of planar and faceted conformal antenna arrays using rectangular patch and bowtie microstrip elements. Both types can be designed for wide bandwidth and low weight using low cost PCB-technology. The array performance has been modelled using infinite array approximations and small finite arrays with Ansoft HFSS and an in-house developed FDTD code. The array designs have been experimentally characterized regarding circuit properties, such as active reflection coefficient, and radiation properties, including active element patterns and embedded array gain. (6 pages)

Digital UHF/VHF antenna

Abstract: The invention comprises a Digital UHF/VHF (DUV) Antenna with a driven DUV antenna preferably boosted by an amplifier mounted close to the DUV dipole and a DUV signal line with antenna, amplifier, and signal line contacts being conductively bonded. The DUV dipole is preferably enhanced by a VHF enhancer and/or by a UHF enhancer comprising one of a reflective and a directive element. The UHF/VHF enhancer preferably includes an RF booster with a reflective element displaced from the longitudinal axis and near the driven antenna to enhance VHF signals. The DUV antenna is preferably configured for DTV reception in the VHF high band range of 174 MHz to 216 MHz, and in the UHF range of 470 MHz to 698 MHz.

Beam-steerable patch antenna array using parasitic coupling and reactive loading

Abstract: A parasitically-coupled and reactively-loaded patch antenna array is demonstrated to achieve beam steering in an analog manner. The strong parasitic coupling between closely-spaced patch antennas is used to form a phased array with a single driven element. The phase shift between the array elements is adjustable by changing the reactive loading on the parasitic patch antenna. A prototype of this antenna array is demonstrated at 2.3 GHz.

Miniatured annular ring loaded patch antennas

Abstract: The proliferation of wireless communication systems has promoted the development of miniaturized antenna designs. Annular ring patch antennas are reported to reduce antenna size. In this paper, several novel compact probe-fed annular-ring microstrip patch antennas are presented. In order to reduce the antenna size and provide a suitable input impedance match, two techniques are employed; the insertion of strips into the annular ring and placing a cross-slot into the ground plane. The proposed annular-ring patch antennas with a cross-slotted ground plane yield a much smaller size for a given frequency and are easily matched to 50 Ohms. These novel patch antennas can effectively be reduced by about 55 percent in size compared to conventional annular-ring patch antennas. The antenna can be designed for single band circular-polarization, dual-band circular polarization, triple band, or wideband operation, depending on parameter selection. Some significant advantages are evident for these structures, such as the centre-frequency exhibiting weak dependence on the position of the feedpoint as well as compact size. Good circularly polarized properties and wide CP bandwidths are obtained for these compact antennas. The multiband versions can provide small frequency ratios. The optimized dimensions for four different type antennas are displayed.

Antenna array including a phase shifter array controller and algorithm for steering the array

Abstract: An antenna system may include an antenna array which includes a plurality of radiating elements. The system may also include a phase shifter controller and algorithm to apply a non-periodic modulation to an excitation of each radiating element.

Reconfigurable Multifunction Antennas: Next Steps fot the Future

Abstract: This paper reviews the state-of-the-art in reconfigurablc multifunction antenna technology, including antennas with compound reconfigurability and integrated switching mechanisms. System-level demonstrations of some antennas are also highlighted. Possible directions for future research in this area are discussed, with an emphasis on bringing reconfigurable antennas together with other system components to deliver superior system performance.

Why Does Reflector Enhance the Gain of Helical Antennas

Abstract: We investigate uniformly-wound helical antennas above ground conductors of various shapes, with aim to determine factors that improve the antenna radiation pattern and gain. We show that the characteristics of helical antennas with large spillover fields can be improved using ground conductors (reflectors). This is achieved by intercepting unwanted radiation and redirecting it favorably. (8 pages)

Proposal of compact MIMO terminal antenna employing Yagi-Uda array with common director elements

Abstract: In this paper, a compact MIMO terminal antenna employing Yagi-Uda arrays with common director elements is proposed. The Yagi-Uda array provides a high gain in the horizontal direction even when the array is arranged horizontally. The size of the proposed antenna is fairly small because the director elements are shared between two Yagi-Uda arrays that face each other and the length of the array is approximately half of two individual Yagi-Uda arrays.

Prediction of Large Array Characteristics from Small Array Parameters

Abstract: An efficient procedure is proposed to predict the performance of large finite arrays from a smaller array. The procedure depends on the knowledge of the mutual admittance matrix of the small array. The mutual admittance matrix of the large array is constructed from the small array ignoring the coupling beyond the small array size. Once the mutual admittance is constructed the effective input impedances of the array elements under different scanning directions and different power distributions are computed. An air filled microstrip antenna is considered. The results obtained using the present method is verified by a full wave numerical analysis of the large array. (5 pages)

Development of Antennas for Subsurface Radars within ACE

Abstract: The paper gives an overview of the joint activities of the ACE-2 partners in the area of antennas for surface penetrating radar. Main areas of joint research and development are discussed and main results of joint activities are presented. Special attention is given to experimental verification of proposed antenna designs.

Reduction of sidelobe levels in interrupted phased array antennas by means of a genetic algorithm

Abstract: Interruptions in the regular lattice of a phased array antenna can lead to elevated sidelobe levels in the resulting antenna pattern. A method for reducing the sidelobe level in such an array is presented, based on the use of a genetic algorithm that modifies the element weights in the array. Results are presented for both scanned and unscanned arrays. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.

Leaf-Shaped Element Bowtie Antenna with Flat Reflector for UWB Applications

Abstract: Recently, a lot of UWB antennas have been reported by many research groups. Most of the reported antennas have omnidirectional radiation characteristics. The disadvantage of using omnidirectional antennas is that the antenna performance can be degraded by adjacent walls or metals. If unidirectional UWB antennas are utilized, the degradation on the antenna performance due to omnidirectionality can be avoided. Another important topic in UWB antennas is the waveform distortion caused by antennas' transmission characteristics. In impulse-based UWB communications, waveform distortions of transmitted and received pulses caused by antennas deteriorate the communication performance. Therefore, the development of UWB antennas having small waveform distortions is highly desirable. In this paper, we propose a novel bowtie antenna using leaf-shaped radiating elements and a flat reflector. This antenna has unidirectional radiation patterns over the frequency range of 3.0 to 10.5GHz. The actual gain in the maximum radiation direction is 6.0-9.0 dBi in the frequency range of 4.5-9.4GHz (relative bandwidth of 71%). The cross-correlations between source pulse and received pulse waveforms are 0.89-0.94, and hence the waveform distortion caused by this antenna is relatively small. As a result, the proposed antenna is useful for impulse-based UWB communication systems using correlation detection.

Array Shape Self-Calibration for Large Flexible Antenna

Abstract: This paper presents a method dealing with the self-calibration problem in term of array shape for large flexible antenna. This implies to take into account the phenomena of distortion and vibration that this kind of antenna, like an array mounted under flexible wing, can suffer from. We propose a technique that eliminates, on the first part, the phase ambiguities due to the large static bending, and on the second part, that estimates an instantaneous array shape. This two-step method allows us to follow the antenna during its dynamic fluctuations due to vibrating modes. We present simulation results in case of two particular large flexible antennas.

A broadband van atta retrodirective array for ka-band applications

Abstract: This paper reported a broadband 8x16 retrodirective array for millimeter-wave applications. The array element is a proximity-coupled dual-ring antenna with a bandwidth of 33.7% (31-42.8 GHz). The antenna is used to build a 4x4 retrodirective array as a sub-array Then the sub-arrays are assembled to form an 8x16 array. The design method of the array and the measured performances from 32 GHz to 40 GHz are presented.

Dual Polarized UHF/VHF Honeycomb Stacked-Patch Feed Array for a Large-Aperture Space-borne Radar Antenna

Abstract: As penetration depth through vegetation and ground becomes more important in active remote sensing applications, there is a shift toward using lower frequencies. To facilitate imaging of ground water, soil moisture and composition, and penetrating through forest canopies, a dual-band synthetic aperture radar (SAR) has been proposed to operate at VHF and UHF frequencies. To accommodate weekly repeat observations from LEO, a swath of roughly 350 Km is needed, requiring a 30-m long antenna aperture from the SAR design point of view. The beams of the UHF and the VHF antennas must coincide in the cross-track direction, resulting in antenna widths of 3m and 11m, respectively. A stacked, linearly dual-polarized patch array feeding a 30 meter diameter parabolic reflector is proposed for this application, which synthesizes near-rectangular effective apertures on the reflector. Using a mesh reflector technology, the mass of such an antenna configuration is about ten times smaller than a corresponding phased-array antenna. A scaled-frequency version of the feed array was initially designed, built, and tested. It was also integrated with a scaled reflector antenna to verify the performance of the overall system. The actual frequency version was then designed, built, and tested. The design of the dual-band stacked array and the power dividers will be discussed, the fabrication process explained, and the approaches used for optimizing the performance characteristics will be presented. The measurement results for return loss on both transmit and receive, isolation, and radiation pattern will be presented and shown to be in good agreement with the simulated results.