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

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Displaying Results 1 - 25 of 211
• ### Broadcast systems: new requirements for antenna designs and propagation knowledge

Publication Year: 1989, Page(s):482 - 483 vol.1
| |PDF (180 KB)

Broadcasting of one sort or another has comfortably existed in the frequency range from 150 kHz to approaching 1 GHz for some considerable time, during which an accumulated wealth of knowledge of radiowave propagation of relevance to the broadcasting environment has emerged. That is not to say, however, that ones knowledge is in any way complete. The phenomenal growth in computing power during the... View full abstract»

• ### Method for measuring impedance of monopole antennas in the range 10-100 MHz

Publication Year: 1989, Page(s):478 - 481 vol.1
| |PDF (324 KB)

A method is proposed for measuring impedances of monopole antennas and for checking the accuracy of the antenna design which does not require a large ground plane. Instead, it is proposed that the impedance measurements be performed for the antenna above a system of radial wires of relatively small length (of the order of one quarter wavelength or shorter at the lowest frequency of interest). Thes... View full abstract»

• ### The assessment and characterisation of the channel provided by a satellite in a highly inclined orbit to land mobile radio units in northern latitudes

Publication Year: 1989, Page(s):169 - 174 vol.2
| |PDF (344 KB)

Satellite mobile communications services for voice and data traffic are being planned for introduction in the mid 1990s. The authors report on preliminary results obtained in Bradford, England. They consider the nature and extent of the attenuation imposed by intervening foliage on the line of sight signal between an elevated (stationary) L-band continuous wave (CW) transmission platform and a lan... View full abstract»

• ### Calculation of broadcast coverage based on a digital terrain model

Publication Year: 1989, Page(s):355 - 359 vol.2
Cited by:  Papers (6)
| |PDF (384 KB)

A new wave propagation model for field strength predictions in the frequency range of VHF and UHF is presented. The basis for the propagation calculations is formed by the Uniform Geometrical Theory of Diffraction (UTD) and the theories for dielectric rough surfaces respectively. Calculated results of models with different complexity are compared with measurements View full abstract»

• ### The satellite: an ideal test range for accurate Earth station antenna measurements'

Publication Year: 1989, Page(s):473 - 477 vol.1
Cited by:  Papers (1)
| |PDF (440 KB)

EUTELSAT, the European Telecommunication Satellite Organization, whose mission is to provide and operate telecommunication satellites currently has four satellites in orbit. There exists a wide range of techniques for antenna measurements for satellite telecommunications, but the author first very briefly demonstrates the domain of antenna measurements by converging the experimental capabilities o... View full abstract»

• ### The on-surface radiation condition approach to electromagnetic scattering

Publication Year: 1989, Page(s):446 - 448 vol.1
| |PDF (196 KB)

The OSRC formulation is used to analyse electromagnetic scattering by a conducting strip and by a dielectric-coated conducting cylinder. The quality of the predictions together with the fact that the method is numerically efficient suggests that the technique will prove useful for application to more complicated scatterers View full abstract»

• ### A four element circular array direction finding and null steering system

Publication Year: 1989, Page(s):168 - 172 vol.1
| |PDF (320 KB)

Describes a small and transportable HF (2-30 MHz) receiving and direction finding system which is also capable of beam/null steering. The system consists of a compact 4-element circular array, processor unit and a standard analogue HF receiver. By using a modified beamformer structure within the unit, the system is capable of direction finding, null steering, and simultaneously direction finding a... View full abstract»

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

Publication Year: 1989, Page(s):374 - 377 vol.1
Cited by:  Papers (1)
| |PDF (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»

• ### Stabilisation of adaptive array patterns using signal space projection

Publication Year: 1989, Page(s):289 - 294 vol.1
Cited by:  Papers (1)
| |PDF (496 KB)

One approach is to use all the array elements but combine them into a number of beams (essentially pointing at the signals) which become the inputs to an adaptive system with the number of degrees of freedom (one per beam) matched to the number of signals. This is the approach taken by Gabriel (1986) and is the starting point for the paper. The authors show that any basis for the signal space (i.e... View full abstract»

• ### An foF2 departure index and its relevance to central European HF signal quality records. II

Publication Year: 1989, Page(s):100 - 104 vol.2
| |PDF (340 KB)

For pt.I see ICAP, York (1987), vol.274, p.182. The author describes work that has been carried out in connection with the use of an foF2 departure index-a daily measure of how F2 critical frequencies have compared with corresponding 27-day medians-and of a composite HF signal quality index which correlates well with it. He presents an investigation of four years duration which provides new data o... View full abstract»

• ### A compact range fed by an array of log-periodic dipole antennas

Publication Year: 1989, Page(s):351 - 355 vol.1
| |PDF (436 KB)

Compact ranges have traditionally used reflector antennas for illumination, but these are typically only usable at high frequencies, such that the reflector is a substantial number of wavelengths in width. For lower frequencies, control of the aperture illumination is better achieved by using an array antenna: the authors describe the design of such an antenna array to synthesise an approximation ... View full abstract»

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

Publication Year: 1989, Page(s):471 - 474 vol.2
| |PDF (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 computat... View full abstract»

• ### Performance of simple diversity antenna arrangements in HF data systems

Publication Year: 1989, Page(s):31 - 35 vol.2
| |PDF (460 KB)

The efficacy of diversity reception in reducing the effects of fading on HF circuits has been recognized for decades. It is particularly useful in HF data systems, where the improvement in bit error rate afforded by diversity can often make the difference between success and failure in a data link. Yet it seems that diversity techniques are often overlooked in many instances where they could profi... View full abstract»

• ### Endfire tapered slot antenna characteristics

Publication Year: 1989, Page(s):432 - 436 vol.1
Cited by:  Papers (5)  |  Patents (1)
| |PDF (368 KB)

Many of the characteristics of endfire tapered slot antennas that make them useful for array applications are discussed. Two different applications have motivated most of the work to date; wideband scanning arrays and focal plane arrays for imaging and multiple beam reflector systems. Typical configurations are presented along with data on impedance and radiation patterns. Recent results disclosin... View full abstract»

• ### Dynamic structure of a transhorizon signal at X-band over a sea path

Publication Year: 1989, Page(s):446 - 450 vol.2
Cited by:  Patents (101)
| |PDF (312 KB)

Preliminary analyses on the time variant structure of a troposcatter signal at 11.5 GHz are carried out in the time and frequency domains. Both the medium term and short term path loss amplitude (dB) distributions are examined. Results on power spectral density and autocorrelation are presented. The joint statistical analysis of durations D of enhancements above a level F is also presented for a p... View full abstract»

• ### Propagation measurements for INMARSAT landmobile satellite paging services

Publication Year: 1989, Page(s):164 - 168 vol.2
| |PDF (316 KB)

The author describes the results derived from a propagation measurement trial performed by INMARSAT in an attempt to assist the design of a potential low cost, portable, and low G/T L-band global data messaging system operating in hostile landmobile channels. Field trials and signal analysis are discussed, and an interpretation of the results is given View full abstract»

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

Publication Year: 1989, Page(s):371 - 376 vol.2
Cited by:  Papers (1)
| |PDF (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 commu... View full abstract»

• ### A computer-based system for radio propagation model management

Publication Year: 1989, Page(s):387 - 391 vol.2
| |PDF (364 KB)

Describes an initial design study for an intelligent (computer-based) model management system for radio propagation prediction on Earth-space links. The system includes deep knowledge' about the relationships between the fundamental concepts used by radio propagation experts. It manages application of the models in particular regions of the world and is able to provide intelligent database suppor... View full abstract»

• ### Field strength forecasting with the parabolic equation: wideband applications

Publication Year: 1989, Page(s):461 - 465 vol.2
Cited by:  Papers (1)  |  Patents (1)
| |PDF (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 purs... View full abstract»

• ### Frequency dependence of absorption attenuation due to hydrometeors

Publication Year: 1989, Page(s):285 - 288 vol.2
| |PDF (224 KB)

In radio wave propagation problems, the attenuation of the electromagnetic signal is due to two phenomena. In the presence of hydrometeors, rain, hail or fog, the energy of the propagating wave will be scattered and also the dielectric losses in the hydrometeors will absorb power from the wave. Both these extinction mechanisms are frequency dependent, especially scattering in the low-frequency reg... View full abstract»

• ### A microstrip antenna of wide angle circular polarization using quarter-wavelength short-circuit patches

Publication Year: 1989, Page(s):135 - 139 vol.1
Cited by:  Papers (1)
| |PDF (304 KB)

Proposes a microstrip antenna with good circular polarization characteristics using a combination of quarter-wave short-circuit patches, and investigates theoretically and experimentally how good, wide-angle circular polarization is obtained using a combination of both rectangular shorted patches and circular shorted patches View full abstract»

• ### Microstrip patch antennas on thick substrates

Publication Year: 1989, Page(s):98 - 101 vol.1
| |PDF (216 KB)

The authors show that a thick patch with an annular gap matching capacitor is an optimum element from a practical design point of view giving wide bandwidth operation albeit at the expense of poor cross polarisation. Feed inductance and radiation pattern effects are investigated and a new patch equivalent circuit is formulated that gives significantly improved results over the existing lumped elem... View full abstract»

• ### Comparison of field-strength prediction methods in the UHF-range

Publication Year: 1989, Page(s):350 - 354 vol.2
Cited by:  Papers (1)
| |PDF (336 KB)

During the last years a great number of different techniques for the field-strength prediction over irregular terrain have been presented in the literature. They may be classified as empirical, theoretical or as combined methods. Field-strength predictions with these different methods using a terrain data bank were compared with predictions according to CCIR-Recommendation 370-5. The results of th... View full abstract»

• ### Microwave antenna metrology from a single intensity scan

Publication Year: 1989, Page(s):468 - 472 vol.1
| |PDF (660 KB)

Two field intensity patterns are recorded at a suitable nearby location and the aperture phase recovered via the Misell phase-retrieval algorithm. A limitation of Misell-based measurements is that the antenna must be defocused for at least one of the intensity patterns. Furthermore the environmental conditions will not be identical. The total measurement and `down time' will be greater than for ho... View full abstract»

• ### Performance of concentric annular patches as a dual frequency band microstrip array element

Publication Year: 1989, Page(s):144 - 148 vol.1
Cited by:  Patents (4)
| |PDF (248 KB)

The concentric ring microstrip antenna is a useful dual frequency band geometry offering good bandwidth with a wide range of band spacing ratios. A disadvantage is that excitation in the TM12 mode leads to larger physical dimensions which may limit beam scanning in some applications. The theoretical model presented for the input impedance gave good agreement with measured values. This p... View full abstract»