Study Of Technology Of Low-Profile Stacked Microstrip Antennas With Different Polarizations

Microstrip antennas have been used widely in current wireless communication systems and present various configurations,among which stacked microstrip antennas could meet the pressing needs,such as wide bandwidth.As the development of equipment conformal and flattening,a low-profile stacked microstrip antenna with high performances becomes an urgent demand.In the case of maintaining a stacked microstrip antenna being low profile,it becomes both key technology and difficulty on how to reinforce antenna performances,including bandwidth,gain,and mutual coupling between radiating/resonant elements.In order to relieve the burden of artificial design,antenna design based on intelligent optimization algorithms to design new structures is an interesting and significant topic.Furthermore,it is crucial to promote human life and production provided that the studies of various application scenarios are implemented on the basis of the properties of stacked microstrip antennas.This dissertation is concerning about the studies of the scientific problems of stacked microstrip antennas in the case of being a low profile,i.e.bandwidth expansion,polarization transformation,and isolation improvement of dual polarization,and several effective solutions were proposed.Additionally,an intelligent optimization algorithm was employed to assist the design and optimization of a stacked microstrip antenna,and a sequence of antennas with different polarizations was produced.The primary research contents are listed as follows:1.A way of expanding the impedance bandwidth of stacked microstrip antenna by shunting low mutual near-field coupling resonators is proposed.Firstly,in the view of the difficulty of introducing a robust resonance capable of varying with the size by stacking structures,by employing the electromagnetic coupling between layers and the improved SRR,a dual-frequency microstrip antenna with a meandered split-ring resonator?MSRR?stacked is presented.Further investigation was carried out where the MSRR was loaded with varactors and equivalent impedance of a NIC?Negative Impedance Convertor?to expand the impedance bandwidth of single frequency band,while maintaining a total profile height of antenna at 0.031?₀??₀ is the wavelength in free space at the center frequency?.Secondly,two low mutual-coupling semicircular split-ring resonators?SSRRs?were devised,which were stacked above the elliptical microstrip antenna,and two additional resonant modes were introduced,combined with the resonant mode of the driven patch to form broadband.The low mutual coupling feature is attributed to the introduction of orthogonal structures on the SSRRs.The proposed antenna was fabricated and measured.Compared to a single-layer antenna without the SSRRs,there are five times as many bandwidth expansions.In comparison to other similar antennas,the proposed antenna possesses compact and low profile features.2.A way of stacking a linear-to-circular polarizer composed of two serial resonators on the stacked layer to achieve low-profile circular polarized stacked microstrip antenna is proposed,and the goal is meeting the application of target detection.Since the designed antennas are mostly loaded with periodic-structure circular polarizer,a low profile cannot readily be obtained.In this dissertation,the dual semicircular split-ring resonators?DSSRs?that constitutes a circular polarizer is stacked above the single-layer linear polarized elliptical microstrip antenna.Based on the symmetry,when reversing the bottom split of the DSSRs,a right-?RH?and a left–handed?LH?circular polarized?CP?antenna,which has consistent impedance,axial ratio?AR?,gain,and efficiency frequency response,can be obtained.Circular polarization radiation is generated according to the DSRRs and is generally elliptic,which inherently contains degenerate modes.The low-profile characteristic and expanded AR bandwidth of the proposed antennas are due to the exploitation of the strong capacitive coupling between the parasitic and driven elements.The proposed antennas were measured.Compared with single-layer elliptical microstrip antenna,the proposed antennas enhance AR bandwidth and gain to meet remote detection.The profile height of the antennas can be maintained at 0.063?₀,which is the halving of the lowest value in similar antennas?with circular polarizer stacked?,and has a wider AR bandwidth.The proposed CP antennas being combined properly can be applied in numerous wireless systems,such as wireless target detection with the capability of detecting the surrounding of targets and chip-less RFID,when it comes to their equal frequency response properties.3.An approach of introducing sub-wavelength structure on the stacked layer to achieve low-profile wideband dual-linear polarized stacked microstrip antenna is proposed in this dissertation.The design is evolved to improve the performances,such as bandwidth,of dual-linear polarized microstrip antenna,mainly by the stacked structures?however,a general approach is the use of feeding layer?.The proposed antenna is stacked with two layers of patches,in which the top layer is a 2?2 patch array.The patches are etched with different slots for impedance matching and good isolation performance.Additionally,a set of stacked complementary split-ring resonators?SCSRRs?are embedded into the stacked patches for the sake of employing their possibly possessing meta-material property.All the stacked patches and SCSRRs can introduce three extra dual-linear polarized resonances for bandwidth improvement.Furthermore,the SCSRRs can be employed to adjust the isolation and impedance matching and improve antenna gain due to their weak left-handed material property.The employment of the capacitive coupling between stacked layers and patches makes the antenna a low profile.The measured results show that the operating frequency band of the antenna is 6.6%?2.34-2.5GHz?.The antenna has an extremely narrow air gap thickness of 0.02?₀,which has an essential impact on its low-profile characteristic?the total profile height is 0.048?₀?.By comparison with similar antennas,the proposed antenna has wider operating bandwidth and approximate port isolation when the profile height is close.4.A design method combining the SA?Simulated Annealing?algorithm to design the stub structures of stacked parasitic element of a dual-layer microstrip antenna is proposed in this dissertation,and wideband property and a series of antennas with different polarizations were obtained.Further investigation was implemented where the designed antennas were constituted into an MIMO antenna for indoor positioning.The designed antenna includes a driven patch etched with an SRR-shape slot,and a parasitic split ring resonator?PSRR?is stacked above.In view of the fact that the majority of antenna designs using algorithms are the optimization of the known antenna configuration and performances,the new antenna structure is obtained automatically by the algorithm.With the control of SA,a sequence of discrete small rectangular sheets was selectively placed nearby the split of the PSRR to obtain the desired stubs.Depending on the reflection coefficient(|S₁₁|)of the antenna calculated in the procedure,the selection and control were reasonably carried out so as to direct the procedure converged step by step.Subsequently,three resonant modes with adjacent resonance frequency and good impedance matching were produced.After further optimization,the final Z-and step-shaped stub antennas were obtained,and the stubs have a significant impact on the antenna performances by electromagnetic coupling.Among the resulting antennas,Z-shaped stub antenna is left handed circular polarized,while step-shaped stub antenna is linear polarized.The Z-and step-shaped stub antennas were fabricated and measured.Moreover,the two antennas are combined into an MIMO antenna with a lower ECC value and a higher channel capacity.