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Ch79-I044963.fm Page 389 Saturday, July 29, 2006 7:14 AM
Saturday, July 29, 2006
Page 389
7:14 AM
Ch79-I044963.fm
389
389
CIRCULARLY POLARISED RECTENNA FOR ENHANCED DUAL-
BAND SHORT-RANGE WIRELESS POWER TRANSMISSION

J. Heikkinen and M. Kivikoski
Tampere University of Technology
Institute of Electronics
P.O. Box 692, FI-33101 Tampere, FINLAND

ABSTRACT

Due to conversion losses, free-space attenuation, and limited transmitted power only a small amount of
DC power can be received from a rectifying antenna {rectenna). In addition to optimisation of the rec-
tenna efficiency, other methods for increasing the applicability of wireless power transmission (WPT) are
also needed. The utilisation of circular polarisation and operation in two frequency bands in order to en-
hance the performance of WPT are demonstrated in this paper. The design and performance of a CP (cir-
cularly polarised) annular ring-slot antenna and microwave rectifier circuit operating at 2.45 GHz and 5.8
GHz ISM (Industrial, Scientific and Medical) bands are represented. The effect of a simple electromag-
netic band-gap (EBG) structure on the antenna performance is also demonstrated and discussed.

KEYWORDS

Wireless power transmission, Rectifying antenna, Circular polarisation, Dual-band, Electromagnetic
band-gap.

INTRODUCTION

WPT comprises both data transmission and transfer of mere electrical power using magnetic or electro-
magnetic fields. In the case of data transmission the purpose of transmitted power is solely to carry a piece
of information from one place to another. The goal of electrical power transfer, however, is transmission
and reception of power high enough to enable the operation of other electrical devices. In short-range
WPT, the distance between the transmitter and receiver can be anything from a few millimetres to about
ten metres. The main differences between data and power transmission are in the amount of transmitted
and received power and in the structure of the transmitter and receiver. If no information needs to be in-
cluded in power transfer, simple continuous wave (CW) transmission can be utilized. Basically the
transmitter then consists of a DC power source, a circuit that converts DC energy to AC energy, and an