Showing papers on "Active antenna published in 1999"

Diversity gain from a single-port adaptive antenna using switched parasitic elements illustrated with a wire and monopole prototype

Abstract: A new concept in single-port adaptive antennas using parasitic elements with switched terminating impedances is presented including results from a concept prototype. Each parasitic element can be effectively terminated in three impedance values. The antenna concept provides multiple radiation patterns with a single RF signal port without the need for RF switches or phase shifters in the direct RF signal path. Impedance variations in the active antenna element are minimized by use of only rotationally symmetric configurations. Measured patterns are used to demonstrate the performance improvement expected using switched diversity combining in a simulated uniform scattering scenario. The concept prototype having one active element and four parasitic elements, is shown to have equivalent diversity performance to between three and four uncorrelated branches.

A new global time-domain electromagnetic simulator of microwave circuits including lumped elements based on finite-element method

Abstract: This paper proposes an extension of the finite-element time-domain method for the global electromagnetic analysis of complex inhomogeneous microwave distributed circuits, containing linear or nonlinear lumped elements. This technique combines Maxwell's equations and circuit equations, directly using SPICE software for the lumped part. Its validation is performed through the study of a strongly coupled two-element active antenna.

Antenna assembly, and associated method, having an active antenna element and counter antenna element

Abstract: An antenna assembly, and an associated method, for a radio device, such as a mobile terminal operable in a cellular communication system. The antenna assembly includes an active antenna element and at least a parasitic element. The active antenna element is of a selected lengthwise dimension and is resonant, in isolation, at a first resonant frequency. The parasitic antenna element is positioned proximate to the active antenna element and separated therefrom by a selected separation distance. The selected separation distance is determinative of a reduction in frequency at which the active antenna element is resonant. Thereby, for a given length, the resonant frequency of the active antenna element is reduced, permitting the lengthwise dimensional requirements of the antenna transducer of which the active antenna element is formed to be reduced relative to conventional antenna transducers.

The influence of electromagnetic environment on operation of active array antennas: analysis and simulation techniques

Abstract: This paper presents an overview of active array antennas, system-level nonlinear effects in such antennas, and their modeling and simulation techniques. Advantages of active array antennas, in comparison with passive array antennas, are discussed. The influence of nonlinear distortions and interference in active antennas on the overall system performance is considered. Modeling and simulation techniques that can be applied to active array antennas are substantially different from those used for circuits and systems. Analytical and numerical techniques are used for the analysis of active antennas, with the prevailing use of numerical techniques at the present time. Electromagnetic-level and circuit-level simulation techniques are discussed. System-level simulation techniques are considered in detail, with special emphasis on their application to active array antennas. The "instantaneous" quadrature technique is proposed as an effective tool for numerical simulation of active arrays over wide frequency and dynamic ranges in a computationally-effective way.

A 10 GHz high-efficiency active antenna

Abstract: This work discusses the use of a microstrip-fed slot antenna to directly provide the necessary output match and harmonic tuning for a 10 GHz class-E power amplifier. There is no matching circuit at the output of the amplifier since the slot is designed to provide the correct impedance at the fundamental frequency and to present an open circuit at the second harmonic. This eliminates losses in the matching circuit and decreases circuit area. Since the class-E amplifier requires a complex output load, the designed slot antenna is not a resonant structure. The device used is an Alpha AFM04P2 MESFET, which has a maximum output power of about 21 dBm. The measured performance of the active antenna shows 74% drain efficiency, 62% power-added-efficiency (PAE), and 20 dBm output power at 10 GHz, at 5 dB gain compression. The PAE is greater than 50% in a 400 MHz bandwidth.

Application of a DC SQUID array amplifier to an electrically small active antenna

Abstract: We have built and operated a wide band electrically small active antenna consisting of a YBa/sub 2/Cu/sub 3/O/sub 7/ half-loop over ground plane antenna, an LTS (niobium) 200 element DC SQUID array amplifier, and low-noise cryogenic GaAs buffer amplifier. These components were integrated with a liquid He flow cryostat into a portable stand-alone package. Measurements of active antenna response from 50 to 500 MHz were made using a transverse electromagnetic cell to illuminate the half-loop antenna. At frequencies below the observed antenna resonance (250 MHz) the active antenna response is flat thereby exhibiting wide band gain.

Integration of a self-oscillating mixer and an active antenna

Abstract: Current trends in commercial communication system developments have called for small-size and low-cost radio frequency (RF)/microwave circuits. One of the solutions is to design a circuit element such that it possesses multiple functionality. In other words, different parts of a circuit are integrated into a single element, and consequently fewer elements are required. In this work, a C-band self-oscillating mixer (SOM) integrated with an active antenna is presented. A dual-gate field-effect transistor (FET) is employed to facilitate the integration. The resultant unit was tested and experimental results are shown to demonstrate the feasibility of the design.

A Novel Single Card FMCW Radar Transceiver With On Board Monopulse Processing

Abstract: This paper presents the design of a complete single card Frequency Modulated Continuos Wave (FMCW) radar transceiver system with a novel four-element active antenna array. Azimuth tracking ability is achieved at the intermediate frequency (IF) via a monopulse processor. The single card FMCW system provides a highly cost effective solution for radar ranging and tracking purposes such as collision avoidance and automated roadways without bulky expensive hardware.

Hybrid analysis/design method for active integrated antennas

Abstract: The paper presents a new hybrid analysis/design scheme where electromagnetic full wave and nonlinear circuit solvers are used in conjunction with an improved Kurokawa (1969) analysis. The full wave solver is the finite-difference time-domain (FDTD) method and is used to extract the scattering parameters (S-parameters) of all passive components and to predict the radiation patterns. The extracted S-parameters are then used in a CAD nonlinear circuit solver to characterise the device line and find an operation point. Note that the effects of the higher order harmonics on the operation point of this active antenna are taken into account by means of the harmonic balance algorithm. To validate the proposed method, an oscillator-type active antenna working at 2.019 GHz is fabricated and tested. It is shown that the calculated and measured results, such as operation frequency and radiation patterns, agree very well.

Optimum design of feed structures for high G/T passive and active antenna arrays

Abstract: In this work, noise analysis of parallel feed structures is presented. Signal and noise behavior of the feed structures are signified by the newly introduced concepts of "coherent" and "incoherent" impedance match of power-combining structures. It is also shown that a feed structure can be redesigned for low-noise operation without affecting the radiation characteristics. Optimum design of parallel feed structures for low-noise operation is explained. Also an optimum use of active elements in such structures is investigated to have a low overall noise temperature of the antenna array with minimum number of active elements. In the analysis, a new method is introduced where a "noise-equivalent line length" (NELL) is defined. This definition, which unifies the contribution of noise from different array elements, is used in the design of a parallel feed structure and as an active circuit replacement criteria in passive arrays.

Director element for radio devices

Abstract: An antenna assembly (12) for a hand-held radio transceiver (10), examples of which include a cellular telephone and PCS device. A multiple element antenna assembly (12) is utilized to provide improved performance characteristics. The antenna assembly (12) may include a conductive radiation director element (30) and a support member (32) for maintaining the director element (30) in deployed orientations. The antenna assembly (12) may be selectively attached to a base portion (42) of an active antenna element (26) of a transceiver (10) or may be pivotally secured to the transceiver (10).

A two-dimensional beam-scanning linear active leaky-wave antenna array

Abstract: This work presents a new technique for electronic two-dimensional beam scanning using a phase-shifterless linear active leaky-wave antenna array. The varactor-tuned voltage-controlled oscillators (VCOs) and coupling network are implemented in this array. The measured pattern of this 4/spl times/1 leaky-wave antenna array shows that the main beam can be continuously scanned from 68/spl deg/ to 40/spl deg/ in elevation as the frequency varied from 8.24 to 9.15 GHz. By tuning the free-running frequencies of the end elements, the main beam can be continuously scanned from -26/spl deg/ to +10/spl deg/ in azimuth. A maximum ERP of 667 mW is measured at 8.9 GHz for this active antenna array.

An active integrated 24-GHz antenna using a flip-chip mounted HEMT

Abstract: In this paper an active integrated microstrip antenna at 24 GHz employing a three-terminal active device is presented. A high electron mobility transistor (HEMT) is integrated in a purely uniplanar microstrip structure by means of flip-chip technology, i.e., all terminals of the passive microstrip circuit are located on top of the substrate and no via-holes are needed. A radiated output power of 10 mW and a dc-to-RF efficiency of 20% are obtained. The deviations of the frequencies of operation from the predicted values are below /spl plusmn/0.5%.

Silicon active slot loop antenna with micromachined trenches

Abstract: A new structure for a slot loop antenna fabricated on a high resistivity P-type(10 kΩcm) silicon wafer is presented in this paper. Wet etched micromachined trenches with conductor hangovers form the slot loop. This method effectively reduces the effective dielectric constant of the substrate and enhances radiation efficiency. The processing methods used and the extension of the antenna configured as a self-oscillating active antenna will be discussed.

Combined UHF and VHF antenna

Abstract: A combined VHF/UHF active antenna, suitable for indoor use, includes a common element that serves as a reflector for UHF signals and as a director for VHF signals. The VHF element is bent upon itself to permit its packaging as a consumer product accessory.

Rectangular Active Microstrip Patch Antennas Revisited

Abstract: Based on a simple, but accurate transmission line model a new formula for location the position of a Gunn diode on a rectangular microstrip patch antenna has been proposed. It also takes into account the intrinsic losses of the patch. Unlike the earlier design formula the present design yields improved spectral purity of the radiated wave, and better radiation pattern. Experimental results have been presented in support of the theoretical conclusions.

Method and device for radio communication

Abstract: The invention relates to a method for reduction of intermodulation distortion in radio communication systems, wherein a signal (S), which is intended to be transmitted, is fed to an active antenna (2) for transmission in a main lobe (13). The antenna (2) comprises a plurality of transmitter stages (5a, 5b, 5n) each of which is supplied with a partial signal (S1, S2, Sn) and comprises an input stage (6), an amplifier (7), an output stage (8) and an antenna element (9). The method comprises a first phase rotation (υin) of each partial signal before each amplifier (7), a second phase rotation (υout) of each partial signal after each amplifier (7), wherein the sum of the first phase rotation (υin) and the second phase rotation (υout) is chosen to a value which is constant, and that said second phase rotation (υout) is chosen so that an intermodulation lobe (15) which is transmitted from the antenna (2) is controlled in a direction which deviates substantially from the direction of said main lobe (13). The invention also relates to a device for reduction of intermodulation distortion.

Amsar active antenna technology and first measured performance

Abstract: GTDAR 1 , under contract of the three MoD of UK, France and Germany, is developing AMSAR, and has been simultaneously integrating and evaluating the PAD laboratory Demonstrator antenna and beginning development of the CAR Antenna airborne Demonstrator. The proposed presentation details some technical and technological solutions implemented into the equipment and how they are evolving from PAD to CAR. Superb performance obtained with PAD supports them and confirms choices were adequate. Proof of amplitude-phase accuracy of T/R module control at antenna aperture is given by recently measured, representative radiation patterns.

A new phase-shifterless scanning technique for a two-element active antenna array

Abstract: In this paper, a new phase-shifterless beam-scanning technique is proposed and demonstrated for a two-element active antenna array. An internal control line with an embedded amplifier is introduced in the array to provide another injection signal other than the mutual-coupling injection signal between antennas. By mixing the effects of the signals from the control line and mutual coupling, the phase difference between antennas is adjusted by gradually changing the amplifier bias on the control line. A dynamic analysis is presented to explain the scanning mechanism. The measured results showed that, when the control-line amplifier was biased from the off state to fully on state, the radiation pattern of the array was varied smoothly from the out-of-phase mode (with 180/spl deg/ radiation phase difference) to the in-phase mode (with 0/spl deg/ phase difference). During the scanning process, the antenna oscillators were stably locked, with the deviation of the locked frequency lower than 0.35%.

Contact localization by multiple active antenna

Abstract: Discusses the multiple active antenna that is simply composed of two insensitive flexible beams placed in the rotational plane, one actuator, one position sensor and one axis moment sensor. The sensor system can detect the contact point between the beams and an object through a simple rotating motion even for the object placed with an inclination angle. During rotating motion, one beam first makes contact with an object. By continuously applying the rotating motion, the second beam makes contact with the same point of the object. Each contact angle is estimated by utilizing both the moment and position sensors. Finally, the contact point can be estimated by the geometrical relationship. The basic idea is verified by experiments.

Vision based active sensor using a flexible beam

Abstract: Discusses a vision based active sensing system, called vision based active antenna (VBAA) composed of a camera, an insensitive flexible beam whose force-deformation characteristic is known, and an actuator for rotating the beam. The camera observes the beam deformation that includes the contact information, while the beam is in contact with an object. By solving a set of equations acquired through the camera, the sensor can detect the contact location and the contact force, even though the contact point is hidden by occlusion. For two particular versions, we show some experimental results to verify the basic idea.

Active antenna panel of multilayer structure

Abstract: The invention relates to an active antenna panel comprising an array of n radiating elements and a multilayer-structure m-beam distributor designed to feed the n radiating elements, the distributor having first “formation” layers for supporting beam-forming means, and second “connection” layers designed to support first electrical connection means for interconnecting the first layers, and second electrical connection means for connection to the radiating elements. In the invention the forming layers extend substantially perpendicularly to the main plane of the antenna, the forming layers and the connection layers are assembled together by molding so that the beam distributor constitutes a single block, and the radiating elements are connected directly to the second connection means.

Suppression of the harmonic radiation from the PBG microstrip patch antenna

Abstract: As a new skill to suppress the harmonic radiation from the antenna we introduce the 2-dimensional photonic band gap structure (PBG) to the ground plane of the microstrip patch antenna. Theoretical and experimental results indicate that the resonance at 1/sup st/ and 2/sup nd/ harmonics can be removed perfectly and the radiation is suppressed at more than 15 dB.

Hierarchical approach to global modeling of active antenna arrays

Abstract: MUGHAL, USMAN AZEEZ. Hierarchical Approach to Global Modeling of Active Antenna Arrays. (Under the direction of Michael B. Steer.) This thesis presents an hierarchical modeling approach to electromagnetic modeling of electrically large planar structures. The computer aided design tool, ArraySim, is ideally suited for modeling active antenna arrays. The structure is sketched in a graphical layout tool which produces a layout file in a CIF format. The CIF file is parsed, circuit ports identified and basis cells assigned. A search algorithm is used to minimize repetitive calculations of elements thus increasing speed and efficiency. An independent MoM analysis tool is called to fill an evolving impedance/admittance matrix, element by element. ArraySim is a complete modeling scheme for spatial power combining arrays targeted at producing tens and hundreds of watts of power at microwave and millimeter wave frequencies. While ArraySim is targeted at spatial power combining arrays, it can be used to model any tri-layer structure if appropriate MoM routines are used. Using ArraySim, we study the behavior of double-slot stripline coupled (SSS) and folded-slot structures. Unit cell as well as arrays are simulated and results are compared with published results.

Second Harmonic Beam Scanning of Active Antenna Array

Abstract: In order to not only obtain a higher frequency radiation but also scan its beam more widely, an active phased array using second harmonic generation is investigated. The active antenna consists of a FET oscillator which plays two roles in fundamental oscillation and frequency multiplying, and the patch antenna resonated at the second harmonic frequency. In the experiments, the radiated beam of the second harmonic wave from the two element active antenna array was scanned more widely than that in the case of the fundamental wave radiation.

Active antenna integrated with up converter for 5 to 24 GHz band

Abstract: Within research toward a new generation of in-door communication systems, utilization of frequencies in the higher microwave and lower MM-wave bands may play an important role in future. One of the barriers to fast market introduction is convenient inherently low cost RF front ends to be realized in planar technology, moreover with integrated antennas. In this paper, a solution for an up converter with an integrated antenna at 5 GHz (non-licensed/HIPERLAN band) to 24 GHz (ISM band) is presented. The results may also trace work on the future 100 GHz systems. A solution with a sector antenna is successfully implemented and described in more detail. The measured results have verified the proposed concept.

Josephson junction phased arrays

Abstract: We propose a design for an active antenna array employing 2D triangular Josephson junction (JJ) arrays as oscillators. The oscillators are kept in sync by coupling their flux trains to that of a serpentine discrete JJ transmission line. Adding external magnetic flux to the line between adjacent oscillators induces a phase shift in their rf voltages enabling beam steering.

High speed optical data link for Smart Antenna Mobile Radio System

Abstract: In order to simplify site installation and reduce related costs, a high-speed Optical Data Link (ODL) connecting active antennas and Base Station in new generation Mobile Radio System has been developed. Using the Smart Antennas System in a three-sector site, the number of feeders becomes unmanageable and costly. Thanks to the Multicarrier Software Radio approach, it is possible to place antenna and wide band RF hardware close together, transporting IF signal in digital format through high-speed serial data bus. The ODL was built up with Low Cost Gigabit Rate transmitter/receiver chipset and Gigabit Ethernet 1300nm Laser Transceiver. A 50-meter fibre cable has been used to cope with the standard antenna tower height (a three kilometre fibre length is also possible for distributed antennas in a microcell deployment). Reference signals like A/D and D/A signal clock, local oscillator (LO) and frequency references are delivered to remote parts by optical link as well. The critical aspect related to A/D clock integrity has been successfully solved.

ESA's ground breaking synthetic aperture radar: the ENVISAT-1 ASAR active antenna

Abstract: The Advanced Synthetic Aperture Radar (ASAR) is a major instrument on board ENVISAT-1. The next Earth observation mission of the European Space Agency. It will represent a sensor of paramount importance for the remote sensing community because of its enhanced flexibility with respect to the existing SARs in the AMI on board ERS-1 and ERS-2. The unique combination of different spatial resolutions, incidence angles, swath width sizes and polarisation diversity will offer an increased number of operational modes tailored for a large set of scientific and operational applications. Among the innovative design features of this radar are the use of an active antenna concept for tailoring the transmit and receive elevation beams to different mode geometries, a digital generation waveform technique for obtaining variable time-bandwidth products and a block adaptive quantization compression scheme. In this paper, the ASAR antenna is described and the development status is presented.