An antenna made of a dielectric disk with a high permittivity mounted on top of a grounded dielectric substrate of low permittivity is analyzed. A numerical procedure based on surface integral equations, derived from the equivalence principle, is used to compute the natural resonant frequencies for the HEM/sub 11/ mode from which the radiation Q factor of the antenna is obtained. Then the radiation pattern of the antenna, operating at the resonant frequency evaluated previously, is computed with an electric dipole excitation located within the dielectric substrate under the dielectric disk. The effect of various parameters on the radiation characteristics of the antenna is studied, and presented in the form of diagrams. The low values of the radiation Q, combined with the high values of the dielectric Q and conductor Q, indicate that this antenna promises to be more efficient then the microstrip antenna. >

A numerical study of a dielectric disk antenna above grounded dielectric substrate

Condition monitoring of an operating apparatus is essential for lifespan assessment and maintenance planning in a power system. Electrical insulation is a critical aspect to be monitored, since it is susceptible to failure under high electrical stress. To avoid unexpected breakdowns, the level of partial discharge (PD) activity should be continuously monitored because PD occurrence can accelerate the aging process of insulation in high voltage equipment and result in catastrophic failure if the associated defects are not treated at an early stage. For on-site PD detection, the ultra-high frequency (UHF) method was employed in the field and showed its effectiveness as a detection technique. The main advantage of the UHF method is its immunity to external electromagnetic interference with a high signal-to-noise ratio, which is necessary for on-site monitoring. Considering the detection process, sensors play a critical role in capturing signals from PD sources and transmitting them onto the measurement system. In this paper, UHF sensors applied in PD detection were comprehensively reviewed. In particular, for power transformers, the effects of the physical structure on UHF signals and practical applications of UHF sensors including PD localization techniques were discussed. The aim of this review was to present state-of-the-art UHF sensors in PD detection and facilitate future improvements in the UHF method.

Application of UHF Sensors in Power System Equipment for Partial Discharge Detection: A Review

A novel internal antenna for hand-held mobile communications is presented. Topics covered include antenna bandwidth, description of the radiation-coupled dual-L antenna, the CAD system for wire-grid modeling, bandwidth, impedance, the shielding case, and the radiation pattern. This radiation-coupled dual-L antenna radiates isotropically, and offers a number of design options for impedance matching. Compared with an inverted-F antenna of equal height, its bandwidth is higher by at least 50%. Numerically calculated results based on a wire-grid model of this antenna agree well with measurement of bandwidth, input impedance, and radiation patterns. A major advantage of this antenna is its enhanced bandwidth without external matching networks in a small occupied volume. >

A new enhanced-bandwidth internal antenna for portable communication systems

According to the structure characteristic and operation performance of the field gas insulation switchgear (GIS), an external ultra high frequency (UHF) sensor, a novel microstrip patch antenna (MPA), is designed to detect UHF partial discharge (PD) signals for the field GIS. The microstrip patch antenna, which receives the UHF electromagnetic wave leaked from the GIS basin insulator, is just mounted on the GIS basin insulator, and has some effect to suppress the surrounding space electromagnetic interference. The analysis and on-site measurements manifest that the MPA working frequency bandwidth is 340MHz to 440MHz, which voltage standing-wave ratio (VSWR) is less than 2, the center frequency is 390MHz, the relative bandwidth is 25.6% up to the wide bandwidth range, and its gain of the maximum radiation and reception directivity is covered 5.38dBi. The laboratory GIS simulation device and field GIS measurements data indicate that the novel UHF antenna sensor has perfect property, higher sensitivity. It is suited for GIS field partial discharge UHF on line detection and diagnosis.

Study of GIS Partial Discharge On-line Monitoring Using UHF Method

A small-sized mobile radio in which its built-in antenna is high enough to enhance the antenna characteristics. In the mobile radio, a base plate (35) is structured by a section (antenna-housing section) including a supply portion and a short-circuiting portion, for example, of an antenna element (36a) which affect the antenna characteristics, and a section (circuit-housing section) which is the rest of the base plate. The antenna-housing section is so positioned as to keep the built-in antenna (36) high enough, that is, to keep the space between the base plate (35) and the antenna element (36a) large enough. On the other hand, the circuit-housing section is positioned toward the back of the cabinet to provide a room for a display (32) and a key section (33).

Built-in antenna for a mobile radio

The variation of voltage standing-wave ratio (VSWR) with frequency for microstrip antennas on stepped and wedge-shaped dielectric-substrates is measured for a band of frequencies, and is compared with those of an equivalent rectangular microstrip resonator. The results indicate a considerable improvement in bandwidth.

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S. Chowdhury

Papers

On some broad-band microstrip resonators

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