Frequency Reconfigurable MIMO Antennas For Wireless Communications

In recent years,frequency reconfigurable antennas have attracted increased attention in modern wireless applications because of their capability to adjust the operating frequency band in response to system requirements and environmental conditions.Frequency reconfigurable antennas are required in many new applications like cognitive radio(CR),advance mobile technology,device to device communication,multiple-input-multiple-output(MIMO)systems,etc.Frequency reconfigurable antennas can be used in combination with MIMO systems to obtain the advantages offered by frequency reconfigurable antennas while maintaining MIMO functionality.Frequency reconfigurable MIMO antennas can enhance the channel capacity and offer higher data rate transmission.Thus,frequency reconfigurable antennas with MIMO configuration are highly desirable for modern wireless communication systems.The purpose of this work is to implement and design novel frequency reconfigurable antennas with MIMO configuration in compact size,that are suitable for wireless handheld devices.The proposed antennas in this research provides wide range continuous frequency tuning while maintaining good MIMO performance.Moreover,a single antenna with both sensing and communicating capability is also proposed for CR applications.Low-profile structures(patch,slot and monopole)are employed in these designs.The advantages of the presented designs are their compact prototype,cost effective,low-profile,planar structure and wide frequency reconfigurability using only one varactor diode per antenna element.In the first design,a reconfigurable microstrip feedline based dual-band frequency agile MIMO patch antenna design is presented.This antenna design contains four symmetrically placed rectangular patch antenna elements.A hexagonal-shaped defected ground structure(DGS)is incorporated into the ground plane for size reduction and isolation enhancement.Varactor diodes are employed within feedline to achieve frequency reconfigurability.The proposed antenna exhibits a wide continuous dual-band frequency reconfigurable characteristic from 1.3 to 2.6 GHz with isolation of higher than 12 dB for the entire band.Then a compact eight-element frequency reconfigurable MIMO slot antenna design suitable for CR front-end applications is introduced.The designed antenna contains eight-elements on a single substrate board and provides multi-band operation.Multi-band is realized by inserting a meandered slot in the center of each antenna element.The proposed design exhibits a wide frequency agile band from 1.6 to 2.48 GHz and two additional bands at 3.6 GHz and 5.2 GHz.Finally,a novel dual-mode frequency reconfigurable MIMO/ultrawideband(UWB)MIMO antenna design is implemented for CR system.This antenna can sense the channel from 1 GHz to 4.5 GHz in UWB mode and provides frequency reconfigurability over wide range between 0.9 GHz to 2.6 GHz in the reconfigurable mode.The novel feature of this antenna design is that same UWB antenna has been utilized in MIMO configuration.The antenna structure contains two symmetrical modified monopole antenna elements and a combination of varactor and PIN diodes.To prove the proposed concept,the prototype of each antenna system is fabricated and measured.All the presented antennas are validated by presenting simulation and measurement results of S-parameters,radiation patterns,efficiencies,envelope correlation coefficient,demonstrating good agreement.These antennas are compact and are printed on FR4 substrate with total substrate size of 120 x 60 x 1.6 mm3,making them promising candidates for modern wireless communication antenna systems,specifically in handheld devices for CR applications.