Showing papers on "Smart antenna published in 1990"

Superconducting antennas

Abstract: It is noted that the advent of high-T/sub c/ superconducting materials has prompted a reexamination of the opportunities for improving antenna performance. Areas where superconductors have potential are considered, including superdirective arrays; large millimeter wavelength arrays; electrically small antennas; matching of electrically small antennas, including large transmitting antennas, and of superdirective arrays; switched line or single line phasers for electronic scanning of arrays; and traveling wave arrays where the transmission line phase velocity controls the beam angle. It is concluded that arrays above 5 GHz will benefit from low conduction, and probably also from low dielectric losses. Matching of electrically short antennas, both small (high-frequency) and large (low-frequency), and of arrays of moderate superdirectivity, will allow significant efficiency improvement. >

Superconducting antennas

Abstract: The applicability of superconductors to antennas is examined with emphasis on the roles of external and internal fields. Six potential implementations have resulted. These are superdirective arrays, millimeter-wavelength arrays, electrically small antennas, matching of antennas, phasers for electronic scanning, and traveling-wave array feeds. Most superdirective arrays are still impractical, because of high Q and strict tolerances. Large millimeter arrays appear feasible, due to a major reduction in feed losses. For electrically small antennas, high Q again limits applicability. However, matching of small superdirective arrays and all electrically small antennas, including large transmit antennas, is very attractive, as matching network losses are greatly reduced. Switched-line phasers offer a major size reduction; phase control by means of temperature of a single line poses some problems. Traveling-wave array beam steering by means of temperature also appears possible. The last two utilize the kinetic inductance provided by thin films. >

Progress on signal-selective direction finding

Abstract: The recently discovered Cyclic MUSIC algorithm for narrowband signal-selective direction finding using antenna arrays circumvents many drawbacks of conventional techniques by exploiting known spectral correlation properties (namely known cycle frequencies such as the baud rate or carrier frequency) of the desired signals to reject undesired signals, interference, and noise. Two recent advances in the capabilities of Cyclic MUSIC are described. The first enables Cyclic MUSIC to simultaneously estimate the directions of arrival of signals having different cycle frequencies instead of having to sequentially process each separate frequency in a list of cycle frequencies (either known a priori or measured). The second advance reduces the sensitivity of Cyclic MUSIC to error in the knowledge of the cycle frequency of interest by estimating the frequency of a quadratically-regenerated sine wave and then using that estimate as the cycle frequency parameter in the computation of the cyclic autocorrelation matrix, which is then processed to estimate the directions of arrival. >

What's new in antennas?

Abstract: Innovative designs, novelty, and creative ideas, currently reported in the international antenna literature, are highlighted in the areas of elements, traveling-wave arrays, apertures, arrays, measurements, and material development. Manufacturing and operational aspects are noted and the driving forces identified. The extent to which antenna technology is mature, the role of research, and degrees of design freedom are considered in some depth. Influences and innovation likely to be experienced within the next five years are conjectured upon, together with some speculation for the more distant future. >

Diversity antenna system for mobile television signal reception - has switching between alternate antenna devices dependent on signal reception level

Abstract: The diversity antenna system has 2 alternate antenna devices which are switched into use in dependence on the reception signal level. The switching to the selected antenna is effected in the vertical blanking intervals of the received signal during 2 successive line synchronisation pulses. Pref. each reception signal level is stored and compared with the signal level for the other antenna, to allow the correct antenna for the next half frame to be selected. USE/ADVANTAGE - Image transmission for remote control of unmanned vehicle, e.g. for handling hazardous materials. Ensures high video reception quality.

Applications of photonic technology to phased array antennas

Abstract: The photonic features that can benefit the system performance of airborne and ground-based array antennas are enumerated. It is pointed out that the wide instantaneous bandwidth is probably the most attractive characteristic, holding great promise for performance improvement of future radar, communication, and electronic warfare systems. The impact of photonic technology on the array architecture design is discussed. The development of a dual-band transmit array (X-band and L-band) controlled by a time shift beamforming network is considered. >

Direction finding in the cellular land mobile radio environment

Abstract: A multiple beam adaptive base-station antenna has been proposed by the authors. The direction finding capabilities of an antenna array form an integral part of the proposed scheme, and so in the paper the ability to determine the azimuth direction of a mobile signal source in a 'city centre' type environment is demonstrated using a four element base-station antenna array. The results show that the close proximity of local scatterers around the mobile reduces the angular spread of the transmitted signal, thus providing credence for this new approach to base-station antenna system design.

Experimental results from a self-calibrating digital beamforming array

Abstract: Experimental results obtained with a self-calibrating 32-element DBF (digital beamforming) array are presented. Results are shown for a variety of beamforming operations, such as the low sidelobe pattern and the adaptive nulling pattern. The effects of errors due to mutual coupling, quantization, intermodulation, multipath, and calibration mismatches were considered. >

Vehicle terminal antennas for mobile satellite applications

Abstract: A review of three classes of antennas for data and voice terminals is presented. The first one is a conically shaped beam low-gain antenna for data terminals. Drooping dipoles, quadrifilar helices, and microstrip antennas are described. These antennas can be simple and inexpensive . The second type of mobile terminal antennas are medium gain: microstrip mechanically steered arrays, microstrip electronically steered arrays, and adaptive arrays with a simple beam-steering system. The third type is a high-gain fixed terminal antenna. The noise temperature and G/T values of some antennas are discussed. The results of the vehicle terminal antennas program at AK Electromagnetique in support of developing North American mobile and fixed satellite services are summarized. >

Fiber Optic Beamforming For Smart Skin Arrays

Abstract: The original objectives of the Smart Skins technology program are reviewed, illustrating the proposed evolution of phased array antennas over the next three decades. In describing this program, particular emphasis is given to antenna performance capabilities, RF feeding, and beamforming. Various beamforming techniques employing phase shifters and optical fiber true time delays are examined. Other aspects of Smart Skin arrays to which optical technologies may apply are reviewed and current technical limitations are addressed.

Coherent optical techniques in antenna beamforming for satellite communications

Abstract: In order to meet the needs of business telecommunications traffic, satellite antennas will be required which can form multiple spot beams and permit extensive frequency reuse, implying stringent requirements with respect to control of beam shape and sidelobe suppression, combined in many cases with rapid reconfiguration and beam hopping or scanning. It is likely that the extensive use of optical technology in critical signal distribution and control functions will provide the key to successful use of active phased array antennas in space. The authors discuss the role of optics in providing not only T/R module interconnection but also transmit and receive beamforming functions for a typical future communications satellite antenna. They emphasize the use of coherent optical transmission and processing techniques, which are seen to offer significant advantages in terms of performance and flexibility.

Mechanically-Steered, Mobile Satellite-Tracking Antenna

Abstract: Signal from satellite tracked in moving vehicle. L-band, mechanically-steered, medium-gain antenna part of prototype radio equipment mounted in vehicle to demonstrate concept of land-mobile/satellite communication system. Provides such services as mobile telephone, voice or alphanumeric dispatch, paging, position-location information, and low-rate data transmission, for users within continental United States and Alaska. Antenna rotated mechanically until it finds direction from which maximum signal comes. Rate sensors provide inertial frame of reference during acquisition, so antenna locks onto signal even when vehicle turning.

A digital beamforming processor for multiple beam antennas

Abstract: A generic digital beamformer architecture that has been implemented to demonstrate the advantages of digital beamforming is described. The digital beamforming processor has been implemented using quadratic residue number system techniques to enhance performance. The custom processor chips are implemented in 1.2- mu m CMOS technology. A digital beamformer can provide significantly better sidelobe performance than an RF beamformer. This is shown for a 64-channel system having only 8-bit weights (I and Q) and 9-bit signals (I and Q). Sidelobe levels can be suppressed 45 dB or better, Practical system implementation considerations are addressed. >

Antennas for direct to home reception of DBS television

Abstract: Outdoor units were required for domestic DBS TVRO stations. Satellites had been ordered to provide 59 dBW EIRP or more, as had receivers incorporating custom DMAC integrated circuits and eurocypher modules. It was established that an antenna aperture width of about one foot would be required and that the antenna could be either a parabolic dish or a flat plate array. Research confirmed that both flat plate arrays and offset-feed parabolic reflector antennas are acceptable to the market. Two Squarial arrays and two reflectors were made available by approved manufacturers in time for launch of BSB programmes. The antennas are designed to facilitate installation by professionals and by the DIY enthusiast. An installation display facility was incorporated in the receiver to monitor the DMAC bit error rate.

Modern analysis methods for medium wave antenna design

Abstract: Antenna arrays, sectionalized antennas, and antennas which are electrically in the vicinity of 1/2 wavelength in length, can be difficult to design. These types of antennas are good candidates for moment method analysis. A few examples are included to demonstrate the usefulness of moment method techniques in practical situations. Moment method techniques are a powerful and valuable tool for the antenna designer. Personal computers are widely available, as are well documented and tested programs such as NEC and MININEC. The existence of this technology has created the opportunity for more complete design capabilities, as well as easier and more certain adjustment processes for the antenna engineer. These techniques must be used with care, as is the case with all problem-solving that involves complex computer programs, but they have become a major modernizing influence on medium wave antenna engineering. >

Quadratic Programming Approaches to New Optimal Windows and Antenna Arrays

Abstract: New window design problems are formulated in terms of quadratic programming. The new windows permit the designer to control the tradeoff between the peak sidelobe level and the total sidelobe energy. In addition, linear constraints can be imposed on the design problem. The proposed methods are applicable to applications in the fields of signal processing and antenna arrays.

Automated antenna test range for small antennas

Abstract: During the past two years the Antennas/Propagation group at NovAtel Communications Ltd has developed a unique automated Antenna Test Range (ATR). This facility is capable of measuring the entire far field radiation pattern of small antennas and displaying the results in two and three dimensional polar plots. This is accomplished by connecting a battery powered transmitter to the Antenna Under Test (AUT) and rotating it about two orthogonal axes. The emitted radiation is sampled over a spherical surface centered about the AUT. The manner in which the measurements are taken permits the hardware for the ATR to be fairly simple and inexpensive, while the software required to gather and process the data is fairly complex. Using this facility NovAtel is able to research and develop unique antennas for future products such as handheld cellular telephones and Global Positioning Systems. This paper presents a general description of the facility's operation and typical test results.

Adaptive phase compensation for distorted phased array by minimum sidelobe response criteria

Abstract: Nonpoint sources are used as the beamforming source for distorted phased array antennas. Since adaptive phase compensation is a nonlinear optimization problem, an appropriate solution is found. A noniterative solution is presented which utilizes a priori knowledge about the sidelobe region of the target field, which is the nonilluminated region of a radar illuminator, to find a phase vector which minimizes the array response in that region. An approximate solution of this phase vector can be found by solving a standard adaptive array problem. Computer simulation results are presented to demonstrate the performance of the proposed algorithm. >

Superresolution effects in broadband antenna arrays

Abstract: The problem of finding the angular 3-dB beamwidth for a wideband Griffiths-Jim adaptive beamformer is discussed. Approximate analytic expressions are presented and their relation to the Cramer-Rao bound (CRB) is considered. Results on the CRB in direction of arrival estimation for a sinusoidal signal are extended to narrowband and broadband signals, together with simple interpretations of their behavior. Superresolution results with a five-element array for three target signal bandwidths (400-2000, 800-1600, and 1120-1280 Hz) are presented. >

Method and apparatus for generating a radiation pattern in the idle state at a group antenna

Abstract: A method for generating a radiation pattern in the idle state in an array antenna with adaptive beamforming by computation, where the terms of the covariance matrix C of the values ​​received from the various elementary antennas of the array signals are determined, and the complex weighting coefficients by which the values ​​of the signals of the different elemental antennas of the array are affected before they are summed to form the received signal can be determined from the system of linear equations, which is defined by the following vector equation: W ^ = AC wherein W ^ is a column matrix that is formed from the different complex weight coefficients of the antenna array, A is any scalar value, Do a column matrix that is formed from the complex amplitudes of the elementary antennas of the array for an incident plane wave Transfer direction is observed, and C

Application of structured method to broadband beamforming in the presence of correlated arrivals

Abstract: The correlation between the desired signal and unwanted interferences exists in situations of multipath and deliberate jamming, and it can degrade the performance of an antenna array significantly. The most of the previous work to decorrelate the correlated arrivals has been for the narrowband case. The paper proposes and analyses a method to decorrelate the correlated broadband directional sources. The method exploits the structure of the array correlation matrix to achieve the performance improvement. >

The measurements column (antenna gain measurement)

Abstract: Four different methods for measuring the gain of circularly polarized antennas under test are presented. Errors that result from these measurements are discussed. The errors presented would form part of an overall error budget analysis. >