Showing papers on "Front-to-back ratio published in 1999"

A uniplanar quasi-Yagi antenna with wide bandwidth and low mutual coupling characteristics

Abstract: We report for the first time a planar quasi-Yagi antenna printed on a single layer of high dielectric constant substrate (Durold, /spl epsiv//sub r/=10.2) which measures 48% bandwidth (VSWR 15 dB and cross-polarization level below -12 dB across the entire frequency band. A very low mutual coupling level of below -22 dB has been measured for a two-element array with /spl lambda//sub 0//2 separation.

Experimental investigations of broadband microstrip antenna for PCS applications

Abstract: The design, numerical simulation and an experimental implementation of broadband microstrip antennas intended for personnel communication system applications at the 1.9 GHz band are presented. A rectangular microstrip patch using multilayer substrate structure with aperture-coupled feed is designed. The prototype has a 10% bandwidth for a SWR<1.2, a 1.90 GHz center frequency, a low front to back ratio and has dimensions. 100/spl times/100/spl times/27 mm. Future work can be carried out by using this antenna in a beamforming antenna array.

Design of aperture-coupled microstrip antenna for applications in wireless communications

Abstract: In this paper, we describe the design and the experimental implementation of a new aperture-coupled microstrip antenna for broadband applications in wireless systems. Using an aperture-coupled feed method, a rectangular microstrip patch employing a multilayer substrate structure was designed and built. The main motivation of this work was to develop large bandwidth antennas for the PCS band 1850-1990 MHz. The new prototype is characterized by a 10% bandwidth around the center frequency of 1.90 GHz and a low front to back ratio. To examine the performances, numerical results, measurements of S-parameters and radiation patterns are presented.

Analysis of characteristics of slot and dipole antennas of georadar with a resistive material

Abstract: When a georadar is working in a tunnel, reflections from metallic mechanisms may be a serious interference. Therefore it is important to enlarge “front to back” ratio of antennas. A spacing between the antenna and the ground surface, which may be due to roughness of the surface, usually diminishes the front to back ratio. A placing of deformable resistive material into the spacing, as proposed by A.G.Chernokalov, increases the front to back ratio.

Testing of a georadar in tunnel drifting

Abstract: The radar [1] has been developed by Moscow Institute of Physics and Technology (MIPT) and joint stock company “Geological Prospecting” Rus. Ltd. Nine months, 3 days a week, the measurements of signals were carried out on the face and top of a tunnel, which is being built in Moscow. The results, obtained by the radar, has been comparing with results of borehole drilling. The ground is clay with limestone layers. Sometimes water infiltrated through thin horizontal layers. The drifting included a path below the Yauza river, at a depth 23 m. The radar uses separate transmitting and receiving antennas. Antenna have size 40×40×10 cm, distance between centers of antennas is 1.1 m. The antennas are of the slot type and have large “front to back” ratio. Due to that they are useful in tunnels, where reflections from metallic mechanisms seriously interfere to the operation of a radar. These antennas were developed in MIPT under leadership of Leschansky Yu.I. It appears that the reflections from metallic mechanisms near the face of the tunnel have unacceptable large amplitudes, in spite of large front to back ratio of the antennas. Roughness of the ground surface or spacing between the antenna and the ground diminishes the front to back ratio [2,3]. Except the metallic mechanisms, placed about 2-3 m from the face of the tunnel, cylindrical metallic part of the tunneling machine with diameter 4 m also give reflections. To increase the front to back ratio of the antennas the using of resistive material has been proposed. Several forms of resistive covering have been tested [1]. Resistive covering includes two blocks with size ~60×20×10 cm, placed on sides of the antenna in E plane, a layer with size 60×60×2÷3 cm below the antenna and a layer 60×80×5 cm above the antenna. As has been proposed by Chernokalov A.G., a layer of artificial easily deformable resistive material has been placed in the spacing between the antenna and the ground surface. That lead to diminishing of electric field in the spacing and attenuation of wave, passed through the spacing to the air. The using of this layer also diminishes a number of oscillations in radiated signal. Moreover, the using of this resistive layer enables to diminish the influence of roughness of the ground surface to the results of sounding. The inconstancy of a signal due to the roughness leads to false “objects” near the ground surface after processing of signals. With using of this resistive layer the number and amplitude of these false “objects” diminish.