Simon Philip Kingsley

Tunability of Liquid Dielectric Resonator Antennas

Dielectric resonator antennas (DRAs) have in the past been used most often at frequencies in the GHz portion of the spectra. This letter presents a novel 50-MHz DRA that uses water as the dielectric. For purposes of keeping the antenna tuned to a specific frequency, ande for using the antenna at different frequencies, this antenna can utilize a pump to alter the level of water in the DRA, thus, altering its resonant frequency. An electronic technique for retuning the feed probe is also presented where varactor diodes are biased to provide a good impedance match across a range of approximately 50 to 100 MHz. These antennas may provide a compact solution at lower frequencies especially where a directional pattern may be required. The liquid dielectric not only provides frequency tuning but simple deployment and a reducible radar cross section.

FDTD simulation of radiation characteristics of half-volume HEM- and TE-mode dielectric resonator antennas

Cylindrical and rectangular dielectric resonator antennas (DRAs) using HEM/sub 11/spl delta//, TE/sub 11/spl delta//, and TE/sub 01/spl delta// mode were examined to see the radiation pattern, impedance, field distribution and resonant frequency that were achieved when the DRAs were bisected through an image plane by a conducting sheet. The resultant half DRAs are smaller in volume and have a more directional radiation pattern. The elevation angle of maximum radiation was lowered in some cases. Finite-difference time-domain simulation techniques were used.

A pure dielectric PIFA for WLAN applications

This paper proposes a new type of antenna for receiving WLAN signals. The antenna is similar in structural design to a conventional PIFA but comprises a pure dielectric as the main radiating device. It is conjectured here that this novel antenna provides electromagnetic radiation through displacement currents and yet is quite different to the well-known Dielectric Resonator Antenna. This paper will describe this Pure Dielectric PIFA (PD-PIFA) and provide simulation and measurement results supporting the previous conjecture. The salient feature of this antenna was found to be its ability to resist detuning when biologically loaded; a 1.25% change in resonant frequency was measured when the antenna was placed in a phantom hand.

Secondary surveillance radar

Secondary surveillance radar is partly a communication system between aircraft and air traffic controllers on the ground; a limited amount of information (aircraft height and flight identification number) is requested by an interrogator on the ground and automatically supplied by a transponder on the aircraft. In the future, this flow of information will increase. Secondary surveillance radar also acts as a radar system because the position of the aircraft is found by measuring the range (from the time delay between interrogation and reply) and the azimuth, as measured by an antenna on the ground. Many of the early problems with SSR have now been solved, and the system is in widespread use throughout the world.

Designing a surveillance radar

Radar surveillance can be improved through the use of narrow beams, but this may lead to there being more beam positions to be searched than is possible in the time available. Multibeam systems can help with this problem, but they put more pressure on the data processing activities, which are often already stretched, even with todays technology. The RCS of real targets fluctuates and its statistical nature must be taken into consideration if the radar detection performance is not to be overestimated. The problem of clutter and the need for sub-clutter visibility is often severe and leads to a need for doppler processing. Careful design of the transmitted waveform is needed to avoid range and/or doppler ambiguities.

Radar studies of the atmosphere

From initially being a nuisance, the scattering of radar signals from the atmosphere has been turned into a useful, and expanding, research technique for the study of atmospheric physics and meteorology. Scattering occurs from discrete sources (rain, birds, etc.) and also from changes in the refractive index of the air, mainly caused by turbulence. Weather radars, investigating lower-atmosphere cloud physics and precipitation, operate at frequencies in S-band and above, but new VHF phased array radars have emerged as a tool for probing the atmosphere from 1 to 100 km altitude.