A. Petosa

A wideband monopole antenna using dielectric resonator loading

As the future of wireless communication steers toward broadband and dual band applications the use of a basic monopole antenna is becoming less suitable. To meet the emerging broadband services a monopole antenna must improve its bandwidth characteristic and provide the same level of simplicity while maintaining its omnidirectional pattern. A proposed new design involves the use of a monopole antenna loaded with an annular ring dielectric resonator antenna operating in the TM/sub 01/spl delta// mode. In this arrangement both antennas produce a uniform horizontal coverage pattern.

A dual polarized microstrip ring antenna with good isolation

This paper presents the experimental results of two dual linearly polarized aperture coupled microstrip ring antennas operating at 1.8 GHz. The use of multiple feeds has resulted in measured input isolation of -30 dB and cross polarization radiation levels of up to -25 dB down from the co-polarization.

Active phased array of dielectric resonator antennas

A novel high gain, low profile active phased array is being developed with electronic beam steering capability in the azimuth plane. The radiating elements consist of multi-segment dielectric resonator antennas (DRAs) of rectangular cross-section, fed by a microstrip line. The array combines DRA technology with multi-layer printed technology. A 320 element array with integrated low noise amplifiers and four-bit digital phase shifters is under development. The array offers high gain, wide pattern bandwidths, and electronic beam steering capability.

Comparison between planar arrays of perforated DRAs and microstrip patches

An array of dielectric resonator antenna (DRA) elements is formed by perforating a dielectric substrate with a lattice of holes. The performance of a 64-element prototype array designed at 25 GHz was compared to a corresponding array of microstrip patches. The perforated DRA array demonstrates a gain improvement of 1 dB and a broader gain bandwidth than the microstrip patch array. This technique of fabricating DRA using perforations eliminates the need to position and bond individual DRA elements in an array.

Microstrip periodic leaky-wave antenna with optical control and beam scanning capabilities

A novel periodic leaky-wave microstrip antenna is presented, capable of dynamic beam scanning using optical control techniques. Optical control is achieved by illuminating periodic silicon elements along the length of the antenna with variable optical intensity. Preliminary results validate the concept.

Feed configurations of CPW fed DRA

A comparison of CPW (coplanar waveguide) feed configurations for the DRA (dielectric resonator antenna) is presented with the goal of optimizing the feed geometry with respect to its topology and radiation performance. Characteristics of CPW capacitive and square loop feeds are discussed. It is observed that the space requirements of the feed and the radiation pattern are dependent on the feed configuration. It is important that the CPW feed is completely covered by the DRA. The square loop feed has the particularly attractive feature of very small area compared to other feeds, making it possible to design it on low permittivity substrates and totally contained within the DRA area. This also leads to reduced excitation of surface waves in the CPW substrate. The H-plane cross-pol level for the square loop feed is much better compared to the capacitive feed due to its completely symmetric nature. Also, it is possible to excite the capacitive slot over the entire slot length or primarily over the CPW trace region by only changing the slot length, thus producing dual-resonance. Fabrication and measurements on the proposed feed configurations are currently being conducted.

TLM-based modal-extraction approach for the investigation of discontinuities in the rectangular waveguide and the NRD

This paper describes the development of a rigorous transmission-line matrix-based modal-extraction approach to analyze discontinuities in guided-wave structures in general, with particular attention to the nonradiative dielectric waveguide (NRD). The motivation for this paper arose from the need to ascertain the admittance of a slot in the ground plane of an NRD without relying on experimental data. These data enabled one to design an NRD-based slot array following the methodology of Malherbe (1984), Malherbe et al. (1984), and Ghosh et al.(1997). Previous work in this area relied on placing observation points sufficiently remote from the discontinuity in order to ensure the decay of scattered evanescent modes to appreciably low levels. The method discussed here obviates this requirement and allows the evaluation of generalized scattering-matrix coefficients arbitrarily close to the discontinuity, thus significantly reducing the computational overhead. Results pertaining to discontinuities in the NRD and the rectangular waveguide have been presented and shown to give good agreement with those in the literature and with measurements. The perfectly matched layer has been used as an absorbing boundary condition in our simulations. Finally, the results have been verified using the power-conservation and Poyntings theorems.

Characterization of an NRD slot for the design of an NRD based slot array

The non-radiating dielectric waveguide (NRD) has been receiving considerable attention due to its low loss nature and the ability to suppress radiation at bends and discontinuities. It is proposed to exploit the above properties to design a NRD based slot array. Previous work relied on measured data for the admittance of a single slot in the ground plane of the NRD. In the present paper, a single slot in the NRD ground plane is characterized using the TLM method. The perfectly matched layer (PML) absorbing boundary condition was used to ensure minimal reflection from the exterior boundaries of the computational domain. It is also shown that an s/sub 11/ less than -40 dB is achieved when the PML is used to terminate the NRD.

CPW-fed DRA

The CPW feed to the Dielectric Resonator Antenna (DRA) has attracted considerable attention in view of the low loss, low dispersion and uniplanar nature of the CPW line compared to the microstrip feed [1]-[4]. Also, the CPW feed is easily amenable to active device integration without the need of vias. In view of the above, this paper illustrates three different configurations of CPW fed DRAs. In the first, the role of Electromagnetic Band-Gap (EBG) structures in the CPW ground plane and in the lower layer of the CPW substrate in increasing the F/B ratio and back-radiation performance is examined. Secondly, a circular polarized DRA is realized using a single coupled folded slot CPW feed. The third design illustrates the performance of CPW fed broadband Multisegment Dielectric Resonator Antenna (MSDRA). The advantages of the CPW feed over the microstrip feed to the MSDRA enhance the versatility and applicability of this antenna. Currently, simulated data on the above geometries using Ansofts HFSS are presented. Fabrication and measurements of the above geometries are being conducted to verify the simulated results.

CPW fed leaky wave antenna using resonance gain

The microstrip fed multilayer leaky wave antenna using the resonance gain phenomenon has been investigated. The motivation for this work arose from the need to design a concealed feed to the antenna which is crucial for the deployment of this structure in a combat environment This paper presents the design of a single CPW feed to the multilayer structure and its radiation characteristics. It is shown that the antenna achieves a resonance gain of about 15.83 dBi at broadside at 20 GHz with a 20 dB F/B ratio, reduced surface wave coupling and good cross-polarisation levels. Measurements are in progress to verify the simulated results.