SPATIAL SPECTRUM SENSING FOR WIRELESS HANDHELD TERMINALS: DESIGN CHALLENGES AND NOVEL SOLUTIONS BASED ON TUNABLE PARASITIC ANTENNAS

This article addresses the major design challenges of antenna systems intended for cognitive transceivers under compactness constraints. The first part of the article provides an overview of the design challenges with regard to sensing over different frequencies and angular directions, referred to as spatial spectrum sensing. The second part describes a novel approach based on parasitic antenna theory aiming at making spatial spectrum sensing feasible for portable lightweight terminals. The idea is to replace the wideband antenna required for sensing over a large bandwidth by a tunable narrowband antenna for both sensing and communication purposes. The flexibility of the proposed antenna system lies in its capability to scan both the frequency and spatial resource dimensions simultaneously via a single RF chain within a miniaturized antenna system. This is done by properly tuning a set of reactive loads connected to a group of parasitic elements closely coupled to the driven (active) element. By doing so, the operational frequency subband leaps to another subband (frequency tuning). Moreover, at every subband, circular permutations of the reactive loads rotate the narrowband beam pattern to different angular positions, giving the cognitive transceiver the capability of sensing over various segments of the space.