M.G. Banciu

Superior Modes in High Permittivity Cylindrical Dielectric Resonator Antenna Excited by a Central Rectangular Slot

High permittivity materials allow good miniaturization of microwave components, but the dielectric resonator antenna using these materials has the drawback of a reduced bandwidth. To overcome this disadvantage we wanted to obtain a relatively wideband high permittivity DRA using the superior modes. Using HFSS simulations, we identified some of the superior modes that appear in cylindrical DRAs situated on a conductor ground plane and excited by a symmetric rectangular slot made in the ground plane. We identified seven superior modes and, for all of them, the measured and theoretically calculated resonant frequencies did not differ by more than 6%. Knowing the possible excited modes in the antenna and the relations for their resonant frequencies, one can predict the operating frequencies of a cylindrical DRA excited by a central rectangular slot.

Compact microstrip resonators for 900 MHz frequency band

A technique to reduce the size of planar resonators is investigated using a transmission line model and a finite-difference time-domain (FDTD) method. New miniaturized square microstrip resonators are proposed for 900 MHz band. The resonators offer low impedance sections leading to a better handling of power. The feasibility of compact filters using the proposed resonators is demonstrated. The input/output coupling lines of a two-pole filter have been positioned in a way that produces a filter response with transmission zeros on the both sides of the pass-band. Sharper skirts and higher out-of-band rejection are obtained for four-pole filters with cross-coupled resonators.

Design of microstrip dual mode filters using finite-difference time-domain method

An accurate full-wave design method is developed for microstrip dual mode filters. The method is based on finite-difference time-domain techniques using Berengers perfect matched layer as absorbing boundary condition. The method was applied to dual mode pass band filters for GSM900 and DCS1800 mobile communication standards. A good agreement between the calculated and measured filters responses was observed.

Aperture Couplings in Multilayer Filtering Structures

In multilayer structures apertures in metallic sheets can be used as coupling elements between resonators located on different layers, allowing very compact filter designs. In this paper, some novel types of planar microwave bandpass filters, using aperture couplings, in structures with three metallic layers, are considered. Couplings between two miniaturized resonators are investigated, by full electromagnetic field simulation. Based on the results of this study, several models of planar microwave bandpass filters, with a single or with two apertures, are designed, verified by simulation, fabricated and measured. Compared to the classical filters, these novel structures show a good compactness and can offer some technological advantages.

BNT advanced ceramics for slot coupled dielectric resonator antennas

Barium neodymium titanate (BNT) material was prepared and characterized. The very high dielectric constant, high Qxf product and controllable temperature coefficient recommend the BNT material for microwave applications. Slot coupled antennas with BNT resonators are investigated. The resonator shape effect on the antenna bandwidth is discussed.

Backward couplers using coupled composite right/left-handed transmission lines

A new asymmetric backward coupler is obtained by edge-coupling two types of composite right/left handed (CRLH) lines. This novel coupler is analyzed in a microwave range (1–10 GHz) and the magnitude of the scattering parameters reveals tight coupling effects (even 0 dB) in a dual frequency band and also very good directivity in the working band.

Design and realisation of star-geometry dual-mode bandpass filter

A design of a planar dual-mode filter is proposed and developed for satellite and wireless communication systems. The novelty of the proposed structure consists of replacing simple diagonal design with a starlike one. This offers the ability of controlling the central frequency and the bandwidth. The filter was implemented on Rogers substrate with 10.8 dielectric constant. The proposed filter structure is 37% smaller in size in comparison with traditional dual mode filters.

Dielectric Resonators for Microwave and Millimeter Wave Applications

Three types of materials for dielectric resonators are presented in this paper. The Pb-BNT materials show the highest dielectric constant (~85). A very small controllable temperature coefficient Tf in the range (-2 divide +4) ppm/degC can be achieved by using dielectric resonators Mg-(Zr_0.8Sn_0.2)TiO₄. On the other hand, the resonators made of Ba(Zn_1/3Ta_2/3)O₃ exhibit the highest values for the Qxf product, ranging from 50000 to 130000 GHz, which make them attractive for millimetre wave applications.

Investigation on microwave signal propagation through some left-handed structures

Some aspects of microwave propagation through left-handed materials are investigated in this paper. The strong distortion of a Gaussian TEM pulse through a material with negative refraction index is studied in the time domain. Moreover, a method of extracting the constitutive parameters of a material by using the scattering parameters of a sample two-port is developed. This method is then applied to some left-handed microstrip structures.

New antennas with dielectric resonators of axial symmetry

New type of dielectric resonator antennas (DRAs) with axial symmetry are proposed for frequencies around 5.8 GHz. Each element uses a high permittivity cylindrical resonator and a low permittivity resonator of a truncated cone shape. Two types of microstrip-fed DRAs were investigated. By coupling the resonance modes, the first type and the second type DRA exhibit fractional impedance bandwidth of 15.6% and 19.7%, respectively.