Antonio Faraone

Antenna Requirements for Software Defined and Cognitive Radios

Antenna requirements for software defined radio (SDR) and cognitive radio (CR) systems are reviewed and the resulting challenges are discussed. Both concepts imply capabilities for operation over very wide bandwidths, of the order of one decade in some cases. This then becomes the main challenge for antenna designers. However, as the concepts evolve, some systems will work over limited bandwidths and existing or extended bandwidth antennas will be used. In the Paper the concepts are explained. As bandwidth is a major concern, the fundamental limits of performance are restated. For handheld radio antenna bandwidth and efficiency at low frequencies is the main problem. Both in the terrestrial fixed infrastructure and in space communication the difficulty of designing very wideband arrays to give the pattern control necessary for interference minimization is significant. In defence applications external handset antennas are seen to be necessary and extension to very wide bandwidths is also seen to be challenging. It is concluded that there is steady progress towards the realization of both SDR and CR, and this is throwing up very significant antenna challenges.

A High-Gain Mushroom-Shaped Dielectric Resonator Antenna for Wideband Wireless Applications

A high-gain mushroom-shaped dielectric resonator (DR) antenna for wideband wireless applications, featuring 65% fractional bandwidth, is proposed. The antenna consists of a low-permittivity hollow cylindrical DR provided with a top-mount spherical cap lens and a metal reflector, excited by means of coaxial probes. Suitable shaping of lens and reflector yields high gain (exceeding 14 dBi) and limited back radiation. The proposed antenna features a broadside radiation diagram with stable radiation patterns and wideband impedance matching. Its potential applications include access points for indoor/outdoor wireless multimedia systems as well as satellite terminal receivers. CST Microwave Studio, implementing a full-wave locally conformal finite integration technique, is employed to design and characterize the antenna, while the singularity expansion method is adopted to express the antenna response to arbitrary excitation waveforms. The numerical results concerning the antenna parameters are found to be in good agreement with the experimental measurements performed on an antenna prototype.

Exact Closed-Form Expression of the Electromagnetic Field Excited by a Uniform Current Distribution Lying on a Cartesian Quadrant

The exact analytical solution of the electromagnetic field distribution produced by uniform electric currents excited on Cartesian half-planes and quadrants is presented. The total field is expressed in terms of geometrical optics (GO) and diffracted field contributions that remain valid for arbitrary observation points and frequency. The jump discontinuity of the GO field is exactly compensated by the diffracted field whose spatial distribution is described in terms of the incomplete Hankel functions and by means of a novel special function. The expression of the diffracted field includes contributions arising from the edges and the vertex of the considered Cartesian domain, illustrating the analytical behavior of the near-field singularities and providing insight into the physical mechanisms governing the field diffractive processes. The proposed solution yields a method to determine the physical optics (PO) response of flat metallic screens excited by uniform plane waves, as well as the fields produced by pulse-shaped basis functions used in the method-of-moments (MoM) solution of electromagnetic problems, showing the relevance of the exact analytical expressions of the GO and diffracted fields arising from edges and vertices of each rectangular pulse domain. Numerical examples validate the accuracy of the proposed field representation.

Experimental near-field method for validating simulation antenna models

Experimental validation of numerical antenna models are performed to verify the model accuracy before their use in larger scale simulations. Model validation is usually performed by comparing to measurements of the antenna or device under test. This verification is highly recommended in RF exposure simulations where the antenna model is employed as source within larger models (encompassing vehicles, human body, pavement, etc.). In exposure simulation, the model verification is required in terms of electric and magnitude fields in the near field (NF) region of the model. NF measurements at distances required for model verification in RF exposure scenarios are difficult and therefore with limited accuracy. The inverse source or equivalent current/source method (EQC) is a post processing technique. It determine equivalent electric and magnetic currents on a volume enclosing the antenna from measured near-field or far-field data. From the currents very accurate near fields on an arbitrary 3D surface can be determined. In this paper, we report the preliminary findings on using the EQC method combined with traditional near-field or far-field antenna measurements in the validation of numerical antenna models in RF exposure scenarios. An UHF monopole antenna working at 380-520 MHz is investigated using noise-free simulated data. The final validation of the method based on the measurement of the UHF Monopole antenna is on-going.

Real-Argument Incomplete Hankel Functions: Accurate and Computationally Efficient Integral Representations and Their Asymptotic Approximants

Novel accurate, computationally efficient integral representations of the real-argument incomplete Hankel functions of arbitrary order are presented, leading to a straightforward numerical implementation. These representations are shown to yield analytical approximants, expressed through known special functions, which are also accurate and valid for any arguments of the incomplete Hankel functions. Through these representations, the electromagnetic field distribution excited in planar and truncated cylindrical structures can be determined accurately and efficiently. Numerical results based on the exact and approximate representations are presented to demonstrate the effectiveness of the proposed integral representations in the analysis of the electromagnetic field distribution excited in complex structures.

Antennas for software defined radio handsets

The concept of software defined radio is reviewed and challenges for antennas are derived. The desire for on-chip wideband transceivers is driving the need for very wideband reconfigurable antennas, and the difficulties of on-chip filtering are indicating that integration of the filter with the antenna is desirable. Reconfiguration of antennas over the decade bandwidths envisaged is challenging and in handheld units external tuner units have been shown to be feasible. However serious problems remain particularly in the large component count and the choice of active device. This paper discusses the technical challenges involved in meeting the developing needs of this fascinating and potentially revolutionary concept.