摘要:

An experimental measurements programme for characterisation of radiowave propagation at UHF band is discussed. Preliminary results on transmission loss, specific attenuation and delay spread are presented and discussed in terms of the biophysical and radio parameters that characterise the propagation path. The results are compared with predictions based on discrete random medium model.

DOI:10.1049/ip-h-2.1993.0051

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The effects of parasitic dielectric resonators on the HE11δand HE13δmodes of a cylindrical dielectric resonator antenna (DRA) have been studied. The DRA was excited electromagnetically with a grounded coplanar waveguide through an aperture in the common ground plane. Strong couplings were observed for the HE11δmode with the parasitic element superimposed on the driven DRA, and for the HE13δmode with parasitic elements placed on both sides of the driven DRA. Results indicate significant enhancement in bandwidth for both modes, and good radiation patterns for the HE11δmode.

DOI:10.1049/ip-h-2.1993.0052

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A compact broadband TE01-mode generator is presented. It consists of five identical sectorial waveguides which are stepped into an ordinary circular waveguide. These sectorial waveguides are fed by five identical probes at the end of a star-shaped feed line with five arms. This feed line is placed in a trace between the sectorial waveguides. A consequence of the five-fold symmetry is that the lowest parasitic mode which can be generated and propagated has a cutoff far above the frequency range of operation (9.5–10.5 GHz). The measurements show that the return loss is less than −15dB in the frequency range of operation. The mode purity is better than 99.4%.

DOI:10.1049/ip-h-2.1993.0053

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Analysis of clear air fading encountered on millimetric wave and infrared radio links are presented. The analysis is based on data obtained during a four-year field study in the city of Riyadh, Saudi Arabia. The region can be considered as a typical arid climate where the rate of evaporation is higher than the rate of precipitation. Maximum rain rate is of the order of 30 mm/h for 0.001% of the year. A brief description of the experimental setup is presented, together with the results of measuring clear air fading experienced by the radio links. Statistical characterisation of fading is given for both the millimetric wave links operating near 40 GHz and the infrared radio link at a wavelength of 0.88 μm. It is shown that fading is dominated by multipath, having a Rayleigh amplitude distribution and an occurrence factor similar to the microwave band. Fades were highly correlated for the two links sharing the same path and separated in frequency by 1%. Multipath fading was also measured on the infrared link. Even at the short hop length at 0.75 km, the occurrence factor was about 1%. Time duration of fades are also analysed, and fade durations were essentially exponentially distributed. Small fades, however, have normal duration distribution.

DOI:10.1049/ip-h-2.1993.0054

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Investigations have been carried out on the nature of variation of characteristic impedance of the TEM cell as a function of thickness and width of the septum for its different offset positions. The impedance is calculated by finding energy storage and power loss inside the cell and using Green's function. Variations in characteristic and wave impedances with frequency of operation are also shown. The electric field distribution in the cross-section for different offset positions of the septum are also investigated and represented graphically.

DOI:10.1049/ip-h-2.1993.0055

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The paper reports on a quadruple-site diversity experiment using 12 GHz radiometers in Austria. Separations between sites were 10.9 to 26.2 km, providing orthogonal path separations (vertical or horizontal) of between 9.3 and 25.9 km. The radiometers were directed along the future look-angle of the ESA satellite OLYMPUS (azimuth 223.16° from true North, elevation 25.43°). The measurements were conducted from May 1980 to April 1983, with dual-site joint uptimes exceeding 94.9% for all combinations. The experimental results indicate that, for this location and geometry, dual-site diversity performance is insensitive to separations above 10 km, all pairs achieving similar diversity gain statistics. The results were close to those predicted by the Hodge model, with the prevailing weather direction having a significant influence on diversity performance. In general triple- and quadruple-site groupings provided better improvement in diversity than the dual-site combinations but, while the statistical improvement was slight, the number of joint events was significantly reduced from dualsite combinations.

DOI:10.1049/ip-h-2.1993.0056

出版商:IEE    

年代:1993

数据来源: IET

摘要:

Distributions of the current and the surface fields close to the corners of a conducting strip with rectangular cross-section are investigated by an accurate and efficient moment method. The strip is made of either a normal conductor or a superconducting material. Based upon this study, a simple graphical procedure for a rough estimation of the finite maxima of the current densities at the edges (corners) is presented.

DOI:10.1049/ip-h-2.1993.0057

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A new technique is presented where the range gain pattern produced by ground multipath interference is considered as a hologram. The technique can be applied to both flat and spherical earth models. Field distribution at the transmitting antenna side is obtained by digital reconstruction from the range gain pattern. Transmitting antenna height and ground reflection coefficient can therefore be predicted. The technique is validated by calculated and measured range gain patterns, and the predicted values are in good agreement with actual ones.

DOI:10.1049/ip-h-2.1993.0058

出版商:IEE    

年代:1993

数据来源: IET

摘要:

A mixed technique is presented for calculating the radar cross-section characteristics of a dielectric-coated conducting cylinder with TE-wave incidence loaded with periodic metallic strips. The technique is based on the spectral-domain method (SDM), conjugate gradient method (CGM) and fast Fourier transform (FFT). Since the property of circular Toeplitz matrix has been used, only memory directly proportional toNsNb(Nsis the number of strips andNbis the number of basis functions for approximating the currents on the strips) is needed, which allows treatment of the cylinder loaded with tens or even hundreds of strips. The RCS of a dielectric-coated conducting cylinder loaded with many periodic metallic strips are first calculated. Numerical results show that the RCS can be effectively controlled by adjusting the period or the spaces between strips.

DOI:10.1049/ip-h-2.1993.0059

出版商:IEE    

年代:1993

数据来源: IET

摘要:

The development of a range of convoluted elements derived from linear and crossed dipoles is traced and their performance is examined experimentally and analytically in relation to their application to frequency-selective surfaces. These configurations give highly packed structures for use on curved surfaces or where maximum separation from the onset of grating responses is required. Two potential methods of analysis are a Floquet modal approach and a spectral iteration. Current distributions on an illustrative example are given. Calculated transmission responses of a convoluted dipole containing three cycles agree well with experiment.

DOI:10.1049/ip-h-2.1993.0060

出版商:IEE    

年代:1993

数据来源: IET