Trevor S. Bird

The Parkes 21 cm Multibeam Receiver

Several extragalactic H I surveys using a λ 21 cm 13-beam focal plane array will begin in early 1997 using the Parkes 64 m telescope. These surveys are designed to detect efficiently nearby galaxies that have failed to be identified optically because of low optical surface brightness or high optical extinction. We discuss scientific and technical aspects of the multibeam receiver, including astronomical objectives, feed, receiver and correlator design and data acquisition. A comparison with other telescopes shows that the Parkes multibeam receiver has significant speed advantages for any large-area λ 21 cm galaxy survey in the velocity range range 0–14000 km s −1 .

A planar resonator antenna based on a woodpile EBG material

A resonator antenna made from a complex artificial surface and a metallic ground plane is described. The complex surface is realized using a woodpile electromagnetic bandgap (EBG) material, which is shown to have a frequency dependent reflection plane location. A highly directive radiation pattern is created due to the angle-dependent attenuation of the resonator antenna coupling to free space. The antenna has the advantages of low height, low loss, and low sidelobes. It is shown that the directivity can be varied over a fixed range by changing the aperture size of the device, with the maximum directivity determined by both the feed element and EBG material properties. The complete bandgap for the woodpile EBG material is confirmed from a band diagram, and its properties as a complex surface are investigated through transmission calculation and measurement. The design of the antenna is described, and two means of exciting the resonator, a microstrip patch and a double slot, are investigated. Theoretical results for these two antennas are calculated the using finite-difference time-domain and are shown to be in good agreement with measured results.

E-shaped patch antennas for high-speed wireless networks

Thin, broad-band, E-shaped microstrip patch antennas (ESPAs), operating in the 5-6 GHz frequency range, are presented. They are intended for high-speed (IEEE 802.11a, 54 Mb/s) wireless computer local area networks (WLAN) and other wireless communication systems. They are suitable for WLAN adaptor cards in the PCMCIA (also known as PC) format, allowing users of current notebook computers to upgrade to this high-speed wireless standard at a low cost. Importantly, our antennas are thin enough to be accommodated in a PCMCIA card of standard 5-mm thickness, without making the antenna end thicker than the card itself. Two different closely spaced antenna pairs are also presented for diversity. A new ESPA configuration with a microstrip feed is presented for easy integration with microwave transceivers. In all cases, within the two IEEE 802.11a WLAN bands (5.15-5.35 GHz and 5.725-5.825 GHz), the reflection coefficient at the antenna input is <-10 dB and in both antenna pairs, mutual coupling between the two antennas is <-20 dB.

The BMRC/NCAR C-Band Polarimetric (C-POL) Radar System

Abstract The development of the first Australian C-band polarimetric/Doppler meteorological radar system (C-POL) is described. Motivated by the need to obtain improved rainfall estimation and the vertical profile of hydrometeors, C-POL was developed jointly by the Bureau of Meteorology (BOM), the Commonwealth Scientific and Industrial Research Organisation of Australia, and the National Center for Atmospheric Research. C-POL is based on a standard operational C-band radar employed by the BOM but modified to be capable of transmitting linear horizontal and vertical polarizations and receiving the co- and cross polarizations on a pulse-to-pulse basis. Standard variables extracted include horizontal reflectivity (ZHH), radial velocity (Vr), spectral width (συ), differential reflectivity (ZDR), differential phase shift (ΦDP), and zero lag correlation coefficient [ρHV(0)]. With the addition of a second receiver chain, the linear depolarization ratio will soon be available. Initial results with the radar are di...

A Reconfigurable High-Gain Partially Reflecting Surface Antenna

A high-gain partially reflective surface (PRS) antenna with a reconfigurable operating frequency is presented. The operating frequency is electronically tuned by incorporating an array of phase agile reflection cells on a thin substrate above the ground plane of the resonator antenna, where the reflection phase of each cell is controlled by the bias voltage applied to a pair of varactor diodes. The new configuration enables continuous tuning of the antenna from 5.2 GHz to 5.95 GHz using commercially available varactor diodes, thus covering frequencies typically used for WLAN applications. Both the PRS and phase agile cell are analyzed, and theoretical and measured results for gain, tuning range, and radiation patterns of the reconfigurable antenna are described. The effect of the varactor diode series resistance on the performance of the antenna is also reported.

The Use of Simple Thin Partially Reflective Surfaces With Positive Reflection Phase Gradients to Design Wideband, Low-Profile EBG Resonator Antennas

Partially reflecting surfaces (PRS) with positive reflection phase gradients are investigated for the design of wideband, low-profile electromagnetic band gap (EBG) resonator antennas. Thin single-dielectric-slab PRSs with printed patterns on both sides are proposed to minimize the PRS thickness and to simplify fabrication. Three such surfaces, each with printed dipoles on both sides, have been designed to obtain different positive reflection phase gradients and reflection magnitude levels in the operating frequency bands. These surfaces, and the EBG resonator antennas formed from them, are analyzed theoretically and experimentally to highlight the design compromises involved and to reveal the relationships between the antenna peak gain, gain bandwidth, the reflection profile (i.e., positive phase gradient and magnitude) of the surface and the relative dimensions of dipoles. A small feed antenna, designed to operate in the cavity field environment, provides good impedance matching (|S11| <; -10 dB) across the operating frequency bands of all three EBG resonator antennas. Experimental results confirm the wideband performance of a simple, low-profile EBG resonator antenna. Its PRS thickness is only 1.6 mm, effective bandwidth is 12.6%, measured peak gain is 16.2 dBi at 11.5 GHz and 3 dB gain bandwidth is 15.7%.

Frequency Reconfigurable Quasi-Yagi Folded Dipole Antenna

A frequency reconfigurable planar quasi-Yagi antenna with a folded dipole driver element is presented. The center frequency of the antenna is electronically tuned by changing the effective electrical length of the folded dipole driver, which is achieved by employing either varactor diodes or PIN diodes. Two antenna prototypes are designed, fabricated and measured. The first antenna enables continuous tuning from 6 to 6.6 GHz using varactor diodes and the reflection coefficient bandwidth (≤ -10 dB) at each frequency is greater than 15%. The second antenna enables discrete tuning using PIN diodes to operate in either the 5.3-6.6 GHz band or the 6.4-8 GHz band. Similar end-fire radiation patterns with low cross-polarization levels are achieved across the entire tunable frequency range for the two antenna prototypes. Measured results on tuning range, radiation patterns and gain are provided, and these show good agreement with numerical simulations.

A hybrid-resonator antenna: experimental results

Experimental results are presented for a hybrid-resonator antenna, consisting of a microstrip patch resonator coupled to a dielectric resonator. They demonstrate a 10 dB return-loss bandwidth of 5.14-6.51 GHz (23.5%) and a radiation pattern similar to that of a conventional microstrip patch or dielectric-resonator antenna. The peak cross-polarization level in the upper hemisphere is at least 18 dB below the peak co-polarization level.

Analysis of mutual coupling in finite arrays of different-sized rectangular waveguides

A Greens function approach is used to analyze mutual coupling in a finite array of different-sized rectangular waveguides arranged on a rectangular grid. In calculating the self- and mutual admittances for mode coupling, a quadruple integration over the source and observer apertures is involved. Possible means of reducing the order of integration are discussed, with the change of variables approach of L. Lewin (1951) being selected. This approach is generalized to allow coupling between different-sized apertures and leads to derivation of mutual admittance expressions for all possible combinations of transverse electric (TE) and transverse magnetic (TM) mode coupling. Calculations using these expressions are shown to be in good agreement with results published earlier by R.J. Mailloux (1969) and measured data for an antenna comprising a square waveguide and two rectangular waveguides. Coupling between closely spaced different-sized square waveguides is also investigated, and for small apertures minimum coupling is shown to occur when the aperture sidelength is about 1.15 lambda . >

A Frequency Reconfigurable Printed Yagi-Uda Dipole Antenna for Cognitive Radio Applications

A frequency reconfigurable printed Yagi-Uda antenna is presented for cognitive radio applications. A 46% continuous frequency tuning bandwidth is obtained by loading the driver dipole arms and four directors with varactor diodes. This configuration allows a high-gain and an almost constant end-fire pattern to be maintained while the antenna operating frequency is tuned. A parametric study was undertaken considering the inter-director spacing, director length tapering, and reflector geometry. It was found possible over the band that the front-to-back ratio is >; 16 dB, the sidelobe level is <; -14 dB and the cross polarization levels in the principal planes are <; - 15.5 dB. From 1-dB compression point measurements, the maximum input power of the antenna with the present diodes is limited to 17.6 dBm at 700 MHz. This suggests that reconfigurable antennas which use active components should have an IIP3 specification placed on them. The frequency selective feature of the antenna makes it as an attractive user terminal antenna for fixed point-to-multipoint cognitive radio enabled broadband wireless access.