الفهرس 
chapter 1Only 14 pages are availabe for public view
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Abstract
Electronically-steerable parasitic array radiator (ESPAR) antenna is a promising antenna array configuration. it offers lower conumption, lower cost, lower hardware complexity, and smaller size as compared to classical antenna arrays configuration. meawhile it is able to support im-portant communication techniques such as beamforming and diversity. in this thesis, we propose a transmitter dipole ESPAR antenna system where symbols are transmitted over swithable beapatterns of the antenna in order tp enhance the power performance of underlay spectrum sharing in cognitive radio netwoeks compared to previousy proposed transmitter systems. we study the performance of two different pattern shapes of ESPAR antenna to choose the appropriate one for underaly spectrum sharing.