Microwave Antenna Applications Research Articles

Effect of Deposition Parameters on the Microstructural Evolution and Electrical Properties of Charge-Balanced Barium Strontium Titanate Ferroelectric Thin Films Deposited on Ceramic Substrates by Pulsed Laser Deposition

ABSTRACTBarium strontium titanate (Ba0.60Sr0.40TiO3) thin films are the main materials of interest in tunable phase shifter for microwave antenna applications. Ba0.60Sr0.40Y0.05Ta0.05Ti0.90O3 thin films, of nominal thickness ranging from 1.7 μm to 2.3 μm, were synthesized on MgO (100) substrates, at substrate temperatures ranging from 500°C to 900°C, at oxygen partial pressures 20 and 50 mTorr, at 500 mJ energy fluence on 3 mm x 1 mm spot size and 10 pulses per second using the pulsed laser deposition technique. All film synthesized at temperatures greater than 500°C were crystalline. The effect of the ionic substitution and substrate temperature in conjunction with the effect of the oxygen partial pressure on the microstructure, and mechanical and electrical properties of the thin films have been studied using shallow angle x-ray diffraction, SEM, nanoindentation, atomic force microscopy (AFM), and focused ion beam analysis (FIB) and are reported in detail. We are currently in the process of measuring the capacitance of these films by various methods.

Dipole and tripole metallodielectric photonic bandgap (MPBG) structures for microwave filter and antenna applications

A photonic band gap structure made from periodic arrays of conducting dipoles and tripoles on a dielectric is presented. Using the proposed structures, several example devices have been demonstrated for microstrip resonators and filters as well as patch antennas. Measured and predicted frequency responses of a microstrip line using a dual dipole metallodielectric photonic bandgap (MPBG) structure show a 40% band width centred at 10 GHz. A planar microstrip resonator using a dipole MPBG shows a slower wave performance and a higher Q factor when compared with the conventional half-wavelength resonator. Three patch antenna designs on different dielectric constant substrates using a tripole MBPG produce better return loss, higher boresight gains (up to 3 dB) and smoother radiation patterns as a result of surface wave suppression.

A 2 1/4-turn spiral antenna for catheter cardiac ablation.

To investigate the delivery of microwave energy by a catheter positioned inside the heart for ablating small abnormal regions producing cardiac arrhythmias, a 2 1/4-turn spiral catheter-based microwave antenna applicator has been developed. The antenna consists of the center conductor with continuous insulating material extending from the coaxial feed cable formed into a spiral antenna. The insulator completely isolates the center conductor from tissue. Phantom experiments were performed on homogeneous tissue equivalent medium. The reflection coefficient of the antenna at different frequencies and for different spiral lengths, the time course and temperature profile of an ablation, and the dosimetry of power versus temperature, all indicate that the high-power heating patterns from this antenna are both wider and deeper than with the other microwave antenna systems and radio-frequency electrodes.

Comparison of bulk DC and microwave surface resistance of explosively fabricated Y-Ba-Cu-O and Bi-Pb-Sr-Ca-Cu-O metal-matrix composite superconductors

Explosive (shock-wave) fabrication has been used to develop simple, monolithic planar sandwich arrays of superconducting YBa2Cu3O7 and Bi7Pb3Sr10Ca10Cu15Ox powder and powder mixtures in a copper matrix and in a complex metal composite of 6061-T6 aluminum, silver and copper. These bulk superconducting arrays have been scaled from planar sizes of 20*25 cm to 25*38 cm; with superconducting channel sizes ranging from 3 mm2 to 10 mm2 in cross section and exposed dipolar strips having areas greater than 1*25 cm. The as-fabricated arrays exhibited shock-wave induced degradation of superconductivity, with zero frequency resistances ranging from 1 to 0.6 k Omega , and microwave surface resistances ranging from 32 to 82 m Omega at 3 GHz and 77 K (liquid nitrogen temperature). Zero frequency superconductivity exhibiting zero resistance at 77 K was achieved by extracting both Y-Ba-Cu-O and Bi-Pb-Sr-Ca-Cu-O consolidated channel sections from the explosively fabricated metal-matrix monoliths and annealing them at high temperature in oxygen or air respectively. Corresponding microwave (3 GHz) surface resistances were then observed to be reduced to around 15 m Omega . The results illustrate the ability to fabricate and scale up a variety of bulk composite superconducting arrays having microwave antenna applications in light-weight structures as well as a host of other potential space applications.

Geodesic Lenses for Aerospace Applications

The properties of a class of geodesic lenses which have potential uses in microwave antenna applications are described. The promising features of these lenses include multiple beam capability and versatility of flush-mounting to a wide variety of surfaces, e.g., flat surfaces on aerospace vehicles and conical surfaces in the nose sections of aircraft and missles. An inflatable lens structure is attractive as a satellite antenna. Because of the circular symmetry of these lenses, coverage over 360° about the symmetry axis is possible. The beam position can be controlled in the transverse dimension by radial feed position giving two-dimensional coverage from a fixed lens. Beam positioning has been demonstrated in two lens models. Furthermore, the TEM and the TEo1 waveguide modes can be employed to obtain two modes of orthogonal polarization.