A Compact Filtering Antenna With Step and Continuous Tuning Modes for WiMAX Cognitive Radio Communication

This work presents a combination of a cup-shaped monopole antenna and an E-shaped Multi-Mode Resonator (MMR) with the presence of a pair of PIN diodes and a varactor diode to form a compact reconfigurable communication filtering antenna for interweave Cognitive Radio (CR) systems. The proposed filtering antenna operates in the WiMAX band, and it is fabricated on an FR4 substrate with overall dimensions normalized to the wavelength (
$\lambda _{o}$
) of the first resonant frequency
$(0.413\lambda _{o}\times 0.516\lambda _{o}\times 0.0165\lambda _{o})$
. The step and continuous tuning serve the secondary user of the WiMAX CR system to communicate in the absence of the primary users at modifiable resonant frequencies and data rates.When the PIN diodes are OFF, the filtering antenna operates with a fixed odd mode resonant frequency and tunable even mode resonant frequency. This state results in a tunable antenna bandwidth covering a maximum measured frequency range of
$3.25-4.02~ GHz$
and a minimum measured range equal to
$3.25-3.58~ GHz$
. The ON state of the PIN diodes eliminates the antenna matching at the even mode resonant frequency while keeping a strong matching at the odd mode resonant frequency. The resulted operational measured frequency range of the antenna in this state is fixed at
$2.9-3.28~ GHz$
. The filtering antenna has acceptable gain values at the pass band of the E-shaped MMR with a maximum simulated gain value equal to
$2.5~ dB$
and a measured maximum gain equal to
$2.48~ dB$
. The simulated and measured power patterns of the antenna for all diodes states are omnidirectional, which are convenient for portable CR gadgets.