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Antennas and Propagation, 1989. ICAP 89., Sixth International Conference on (Conf. Publ. No.301)

Date 4-7 Apr 1989

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Displaying Results 1 - 25 of 211
  • Full-wave analysis of stacked rectangular microstrip antennas

    Page(s): 369 - 373 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    The authors present a full-wave analysis of stacked rectangular microstrip patch antennas. The analysis, which is based on the spectral domain technique, makes use of the electric field integral equation in conjunction with Galerkin's technique for coverting this equation into a set of linear equations. In the formulation of the problem they assume that the lower patch is excited by an idealised electric current probe. The developed technique is applied to several stacked rectangular patch antennas including to those with two equal patches of accurately aligned edges and of displaced edges. The technique is also applied to investigate the effect of sizes of patches on resonant frequencies, bandwidth and input impedances. Experimental results for the above cases are presented to verify the numerical results View full abstract»

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  • Personal communications systems-new requirements for antenna and propagation knowledge

    Page(s): 371 - 376 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    Concentrates on the antenna and propagation issues that will need to be addressed in order to bring the concept of personal communications into reality. The author begins by defining the personal communications concept in sufficient detail to place some bounds on the system design and network planning requirements. This leads into a consideration of the physical environments where a personal communications system is likely to be used, an outline of the propagation conditions expected to be encountered, and a consideration of the antenna requirements of these systems. Where appropriate, the argument is illustrated by examples from the literature View full abstract»

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  • Field strength forecasting with the parabolic equation: wideband applications

    Page(s): 461 - 465 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    The desire to make field strength predictions for the more complex structures that give rise to surface and elevated ducts (such as coastal advection and subsidence inversions) has led to a renewal of interest in an alternative full-wave method of solving Maxwell's equations-the parabolic equation method. Although introduced into radiowave propagation by Leontovich and Fock (1946), it was not pursued due to a lack of suitable numerical methods of solving the equation at that time. Recent advances in an analogous problem in underwater acoustics have led to the development of a powerful, general, numerically efficient method for radiowave propagation View full abstract»

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  • Reactively and resistively loaded wideband whip antennas: possibilities and limitations

    Page(s): 399 - 402 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    The author offers guidelines on the limitations of wideband whip antennas. A very large number of antennas are analysed numerically, together with their matching networks, and optimal combinations of antennas and matching networks with respect to certain requirements are found. These optimal combinations are regarded as the best antennas (integral with their matching networks) and the results are summarized in a number of diagrams View full abstract»

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  • Optimal choice of basis functions to analyse microstrip antennas with the method of moments

    Page(s): 374 - 377 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    The authors discuss antenna analysis, briefly presenting related theory, and consider a solution to the convergence problem. Limitations of the analysis method are outlined, and the use of edge expansion functions is introduced View full abstract»

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  • The wideband feed system on the Australia Telescope

    Page(s): 163 - 167 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    From the outset the Australia Telescope has been designed to permit operation over a very wide frequency range covering frequency bands within the range 1.25-116 GHz. The lower end of this range is determined by the requirement to observe red shifted hydrogen which has a line at 1.42 GHz while the upper limit is to encompass the carbon monoxide line at 115.3 GHz. Extending the operation of the telescope down to the deuterium line at 327 MHz is also anticipated as is the inevitable increase in the number of bands required for observations within this extensive frequency range. Given a 22-m dia. Cassegrain antenna is to be the array element, the optics and feed system necessary to cover the very wide frequency range provides a formidable challenge to the antenna designer. The authors give an overview of the feed system that was developed to meet these demands View full abstract»

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  • Microwave holographic imaging of intermodulation product sources applied to reflector antennas

    Page(s): 463 - 467 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Reports on a new form of microwave diagnostic imaging that enables sources of IMP on a reflector antenna to be located. The problem of IMP generation by reflector antennas has been reported by a number of workers including Higa who observed IMP generation due to the metal-oxide-metal (MOM) junctions present on a large aluminium reflector antenna, and Ghione and Orefice who have reported on IMP produced by a carbon fibre reflector. Microwave holographic imaging is now a well established method of antenna diagnostics. By adapting these techniques it is possible to scan a reflector to locate sources of IMP on its surface. Initial obtained by these methods have already been reported, but the authors present further developments including results obtained from a paraboloid reflector View full abstract»

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  • Estimation of signal levels in evaporation ducts using ray theory and their comparison with experimental measurements

    Page(s): 471 - 474 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    A comprehensive computer program based on ray theory, has been developed for the estimation of signal levels in an evaporation duct. The computations were made for a radar situated near Indian east coast operating at a frequency of 3 GHz with an output power of 75 kW. The two ray interference theory coupled with the basic ray tracing technique is utilized to carry out the propagation loss computations. These are compared with the signal levels observed with the radar under anomalous conditions. Radar ranges up to 100 km in an evaporation duct can be explained with the help of the ray tracing program developed. The program can not be applied to explain radar ranges about 500 km and more and a wave hop method is required for which work is in progress View full abstract»

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  • HF Doppler radar observations of equatorial plasma drifts and spread-F

    Page(s): 186 - 190 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The HF Doppler radar technique has been proven to be a valuable means for studying plasma motions in the F region of the equatorial ionosphere. The authors present, for magnetically quiet conditions, the Doppler observations dealing with (i) the postsunset vertical plasma drifts and their seasonal dependence, (ii) the prereversal enhancement in the vertical plasma drift and the occurrence of equatorial spread-F, and (iii) the vector plasma drift measurements for a sample equinoctial day View full abstract»

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  • Transient response and WKB second approach

    Page(s): 400 - 402 vol.2
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    Presents a theoretical analysis of transient EM wave propagation in a loss medium. A solution is also presented of the wave equation in a slowly varying stratified medium with reference to WKB second approach View full abstract»

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  • Printed antennas in multiple layers: general considerations and infinite array analysis by a unified method

    Page(s): 364 - 368 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    Infinite array analysis is described, and experimental results from a waveguide simulator are discussed. Considerations for the use of a stripline-aperture-coupled microstrip antenna geometry are given, and further research plans are outlined View full abstract»

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  • Ground-based radiometric observations of atmospheric emission at 20.6, 31.65, and 90.0 GHz

    Page(s): 229 - 233 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    The Wave Propagation Laboratory (WPL) has designed, constructed, and field tested several ground-based microwave radiometers to observe the atmosphere. Extensive experience has been gained by using both zenith-viewing and steerable dual-frequency instruments operating at 20.6 and 31.65 GHz. These instruments provide unique and meteorologically useful observations of precipitable water vapor and integrated cloud liquid. Perhaps equally as useful are the microwave attenuation characteristics that these devices can easily provide. The WPL extended its radiometric capabilities by adding a channel at 90.0 GHz to the steerable and transportable radiometer. All three channels on this radiometer have equal beamwidths of 2.5°, and point in the same direction from the same location; hence, they are capable of simultaneously measuring emission and deriving attenuation for the same volume of air. Examples are presented of some of the data taken with the new system at San Nicolas Island, California, USA, and at Denver, Colorado, USA. From these data, several statistical and physical quantities, relevant to radio propagation studies, are derived and compared with theory View full abstract»

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  • Measurement of high resolution radio-refractive-index at a tropical Indian latitude

    Page(s): 239 - 242 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    Radio refractive index (RRI) variation in the troposphere has been subject of sustained interest because of its important role in microwave radio communication. The authors present the results of first Kytoon sounding at a microwave repeater site, Chaprola 30 kms south east of Delhi. A sensor package was used with temperature sensor accuracy of ±0.01°C (both dry & wet bulbs) and pressure ±0.1 mb. A maximum height of 202 m above the surface was attained View full abstract»

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  • Radar wave propagation in an inhomogeneous evaporation duct

    Page(s): 466 - 470 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    The propagation of radar electromagnetic waves above the sea surface is dependent upon the atmospheric conditions. Inversions in the temperature and humidity profiles above the sea are responsible for the creation of various types of duct layers. In such duct layers the EM wave propagation can be regarded as a waveguide. Special interest is given to cases where the (modified) refractive index profile correspond to duct layers of 10-40 m height known as the evaporation duct. A solution is presented for slow variations corresponding to an inhomogeneous behaviour of the atmospheric conditions as a function of the distance View full abstract»

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  • Omnidirectional radiation patterns from body mounted microstrip antennas

    Page(s): 187 - 190 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    Presents the results of an investigation carried out to develop microstrip body-mounted antennas designed to have an omnidirectional radiation pattern in azimuth, at a frequency within the 100-440 MHz range. Among the body-mounted antennas tested were a single rectangular patch microstrip antenna, an array of two rectangular patch antennas and a novel, helmet-mounted travelling-wave microstrip antenna View full abstract»

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  • The first radio-optical telescope

    Page(s): 540 - 546 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1948 KB)  

    In 1958 the author proposed a double-mirror antenna for a large radio telescope to be constructed in the mm, cm and dm ranges having a main stationary sphere-shaped mirror and a small movable correcting mirror providing a wide-angle scanning with no beam distortion. A theory started to be developed along with a design project for this type of antenna with an original system of automatic control. Started in Armenia in 1960 and completed in 1963 was the construction of the first antenna of this type having the main mirror 5 m in diameter with a functioning aperture diameter of 4 m. At that time it was the world's largest antenna for the short-wave part of the mm range. In 1985 the work was completed on mounting and installation of the whole construction and building complex of the world's first radio-optical telescope with a large antenna having a stationary spherical main mirror of 54 m in diameter and the operating aperture diameter of 32 m. For the first time ever in telescope construction the antenna was combined with a large optical telescope. The main mirror diameter of the optical telescope is 2.6 m View full abstract»

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  • Diversity gain and rain height statistics for slant paths from radar measurements

    Page(s): 340 - 344 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    A dual polarized S-band radar was used in a year long experiment to study the prediction of slant path attenuation from radar data. As a part of this experiment, a large number of RHIs (vertical radar scans) were made during rain events. The data from these events has been analyzed to determine the statistics of rain height and melting layer thickness. Diversity gain statistics can be obtained from predictions of attenuation on synthesized slant paths in the RHI planes. Diversity gain for three paths is examined: one artificial path and two paths for which beacon attenuation measurements are available. Excellent agreement is obtained for diversity gain from the radar predictions and the beacon measurements View full abstract»

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  • HF propagation over a trans-auroral path

    Page(s): 19 - 22 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    The high latitude ionosphere forms a highly dynamic and disturbed medium which can severely affect HF radio signals propagating through these regions. In order to investigate the characteristics of the type of propagation, a frequency agile transmitter has been installed north of the auroral oval on Baffin Island in the Canadian North West Territories, together with a receiver and data logger located at Leicester in the UK. Experiments are currently being undertaken on signals transmitted over this trans-auroral path on fourteen frequencies between 3 MHz and 21 MHz, radiated with a power of approximately 350 W. Results of measurements undertaken during a 30 day period in July and August 1988 are presented View full abstract»

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  • Low profile antennas and arrays for satellite navigation

    Page(s): 131 - 134 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    The Global Positioning System (GPS or Navstar) is a highly accurate navigational aid, which relies on receiving circularly polarised signals at 1575 MHz (L1) 1227 MHz (L2) from a number of satellites scattered across the upper hemisphere. The signal bandwidth is 20 MHz at both L1 and L2, with a relatively flat pass band response, so that the 3 dB bandwidth of the antenna is significantly greater than this (50-100 MHz). The antenna radiation pattern needs to be very broad, maintaining good coverage close to the horizon. For aircraft applications in particular, a low profile antenna is required, suggesting a printed or cavity backed approach. A single printed patch antenna can give circular polarisation on axis, and a uniform pattern in azimuth, but does not have a sufficiently broad elevation pattern View full abstract»

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  • A novel accelerated convergence technique for adaptive antenna applications

    Page(s): 331 - 335
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    The authors introduce a novel adaptive antenna scheme. The technique involves the use of a fast digital processing algorithm in an adaptive feedback loop arrangement to compute updates for an analogue beamformer weighting circuit. This ensures a scenario-independent convergence performance, and because of the feedback path, can accommodate beamformer circuit errors and nonlinearities without undue degradation of the achievable cancellation performance View full abstract»

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  • Lateral pulse wave propagation in lossy weak fluctuating random media. II. A mutual coherent function

    Page(s): 403 - 405 vol.2
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    The analytical solutions of transient fields and their coherent functions for coherent lateral pulse waves, are derived by means of Fourier transformation and HF narrowband approximation. Numerical results reveal that the mutual coherent functions vary fluctuatingly as a function of difference between carrier frequencies. The oscillating amplitude increases as the difference of carrier frequencies decreases View full abstract»

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  • Towards a 3:1 band phased array

    Page(s): 178 - 181 vol.1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    A multielement phased array antenna has been developed to demonstrate the feasibility of broadband operation. Quadridged waveguide horns were employed as antenna elements to achieve wide bandwidth and polarisation diversity. The elements were arranged into two offset linear arrays to reduce inter-element spacing at the higher operating frequencies. A feed network has also been constructed employing MDS custom designed GaAs MMICs for both the switches and phase shifters. Phase alignment of the antenna array and feed network has been successfully completed for linear polarisations. Once aligned the system has demonstrated reasonable scanning performance for both vertical and horizontal polarisations. The gain of the antenna array and feed network has also been measured. At fo the measured values gave close agreement with predicted results View full abstract»

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  • Tropospheric communication in arid zone with space diversity

    Page(s): 46 - 48 vol.2
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    Describes the results of a series of experiments conducted on a 158 Km path between IIT Delhi and CEERI Pilani. Most of the path towards the Pilani side is almost desert while it is rocky and inhabited towards the Delhi end and can be broadly classified as a mix desert and continental subtropical climate path. The system operates in 4.4 GHz to 5 GHz band, and has the capability of two way communication in a full duplex mode. Each terminal has two transmitters with two power amplifiers capable of 1 kW output. The receiver utilizes a parametric amplifier with a noise figure of 4 dB. Dual polarized parabolic antennas of 3.05 m diameter are used. One of the most efficient and widely used protection against the effect of multipath, is the space diversity technique. This technique takes advantages of the decorrelation between the received signals by two separate antennas. The separation between two antennas can be varied between 45 and 100 wavelengths. Results based on long term experiments provide a better understanding of the behaviour of a space diversity reception. The fading distribution, the fade depth and the degree of correlation between fading over two horizontally spaced antennas, when the link is in an arid zone, appear to follow the known general trends View full abstract»

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  • Influence of obstacles on VHF TV signal propagation

    Page(s): 367 - 370 vol.2
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    Propagation measurements are conducted over 13 paths mostly in Western India. All the paths are chosen in such a way that they constitute single knife edge diffraction propagation paths. The fieldstrength data has been collected utilising Bombay, Poona and Srinagar TV transmissions. Out of the 13 paths chosen in this study 5 fall in the region around Bombay transmitter, 6 around Poona and 2 around Srinagar region. Both Bombay and Srinagar transmitters operate on channel 4 (61-68 MHz) and kPune operates on channel 5 (174-181 MHz). The e.i.r.p. of Bombay, Poona and Srinagar transmitters are 56 kw, 7.2 kw and 50 kw respectively. The observed fieldstrength values are converted into path loss values and compared with those obtained from different prediction methods View full abstract»

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  • Experimental studies on millimeterwave and infrared propagation in arid land: the effect of sand storms

    Page(s): 268 - 270 vol.2
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    Summarizes the measured sand/dust storm parameters and its effect on the radio links. Nine sand storms were experienced in the city of Riyadh during 1987, and were observed both by the meteorological sensors and by the radio links. The measurements were used to determine the prominent storm parameters which have considerable effects on wave propagation into such storms. Such parameters include particle concentration, particle size and size distribution, and refractive index of such particles, or its dielectric constant. As the moisture content of sand/dust particles increases, attenuation increases markedly. The measured attenuation, as the millimetricwaves propagate through sand storms, is compared with the calculated value of attenuation. Such calculated attenuation is found by using an attenuation model which relates attenuation to visibility, frequency and particle size and refractive index View full abstract»

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