Study Of Reconfigurable Antennas Based On Metamaterials

Reconfigurable antennas(RAs)are the frontier of the current antenna research and excellent antenna candidates for future advanced wireless or satellite communication applications.The physical structure of a reconfigurable antenna is unchanged,by utilizing electrical,mechanical or other methods to change its fundamental operating mechanism,and the frequency and radiation characteristics of the RA can be varied significantly.The reconfigurability makes the single antenna equivalent to multiple antennas with fixed functionalities.On the other hand,metamaterials,such as left-handed materials(LHMs),frequency selective surface(FSS),metasurface(MS)and electromagnetic band gap(EBG)structures,are widely utilized in antenna design.In comparison with conventional antennas,these new antennas have better performance.In combination of metamaterials and antenna,a wideband circularly polarized antenna and two polarization reconfigurable antennas based on metasurface superstrate,a dual-band antenna and a pattern reconfigurable antenna based on mushroon-like superstrate,two metamaterial-based antenna arrays,and a frequency reconfigurable antenna integrating with high impedance surface(HIS)are proposed.The main contributions of this dissertation are as follows:1.A wideband circularly polarized antenna using metasurface superstrate for C-band satellite communication application is proposed.The proposed antenna consists of a planar slot coupling antenna with an array of metallic rectangular patches which can be viewed as a polarization-dependent metasurface superstrate.The metasurface is utilized to adjust axial ratio(AR)for wideband circular polarization.Furthermore,the proposed antenna has a compact structure with a low profile of 0.07?0(?0 stands for the free space wavelength at 5.25 GHz)and ground size of 34.5x28 mm2.Measured results show that the-10 dBimpedance bandwidth of the proposed antenna is 33.7%from 4.2 to 5.9 GHz,and 3-dB AR bandwidth is 16.5%from 4.9 to 5.9 GHz.The simulated and measured results are in good agreement to verify the good performance of the proposed antenna.Basing on this antenna,two polarization reconfigurable antennas are designed.One is integrating PIN diodes and chip inductors on metasurface superstrate,by controlling the PIN states,the antenna can switch between linear polarization and left-hand(or right-hand)circular polarization.The other one is etching a "×" shape slot on the antenna ground,then welding PIN diodes on the slot,through controlling the PIN states at different position,the antenna can switch among linear polarization,left-hand circular polarization,and right-hand circular polarization.2.A rectangular mushroom-like superstrate structure is proposed to design an antenna for dual-band wireless local area network(WLAN)applications.The proposed antenna consists of an array of mushroom-like rectangular patches and a planar slot antenna.The proposed antenna can operate in two bands.The lower band is from 2.3 GHz to 2.98 GHz,with-10 dB bandwidth of 25.8%and average gain of 2.0 dBi,which is corresponding to zeroth-order resonant(ZOR)mode,and the upper band is from 5.02 GHz to 5.84 GHz,with-10 dB bandwidth of 15.1%and average gain of 6.9 dBi,which is produced by TM10 and antiphase TM20 modes.The proposed antenna is feasible to cover the specification for dual-band WLAN applications in the 2.4 GHz(2400-2484 MHz)and 5 GHz(5150-5825 MHz)bands.Furthermore,the proposed antenna has a low profile of 4.2 mm and compact size of 33x30 mm2,which is suitable for installation in wireless handheld devices.The simulated and measured results are in good agreement to verify the good performance of the proposed antenna.A pattern reconfigurable antenna is designed based on this antenna.Except the array of mushroom-like rectangular patches and planar slot antenna,a simple DC biased circuit is implemented in the pattern reconfigurable antenna.By the control of biased circuit,four reconfigurable patterns and an overlap-10 dB bandwidth of 8.7%can be achieved.3.On different application background,an antenna array composed by wideband circularly polarized antenna using metasurface superstrate and an antenna array composed by dual-band antenna utilizing rectangular mushroom-like superstrate are designed,simulated,and analyzed,respectively.Results show that the axial ratio of the circularly polarized antenna array turns from single wideband to dual narrow bands with scanning angle increasing,which has good circular polarization property.When the dual-band array scans,scanning compensation from lower band is implemented on upper band,which greatly broadens the scanning angle.Furthermore,there is almost no scan blindness along the array direction.4.A frequency reconfigurable antenna(FRA)which consists of quasi-Sierpinski fractal dipoles integrating with dual-band high impedance surface(HIS)is proposed.The antenna can operate in three frequency bands,i.e.X-band,Ku-band,and Ka-band,by changing the states of PIN switches.In order to achieve a low-profile design and good front-to-back radiation ratio,a dual-band HIS is presented as a reflector.The HIS is composed of an array of square patches with etching square slots,which has two in-phase reflection bands for X-and Ku-band and can be viewed as an artificial magnetic conductor,while as a metallic electric conductor in Ka-band.So the antenna has a unified profile of 3.754 mm for different reconfigurable frequency bands.An ideal switch prototype of FRA was simulated,practical PIN switch models of FRA and 2x2 FRA array with bias lines were fabricated and tested,and finally an 8×16 FRA array is designed and simulated.Results indicate that there are good impedance matching and radiation feature on X-band,Ku-band,and Ka-band for the proposed antenna and antenna array.