Wideband Circularly Polarized Antennas With Parasitic Loading

As the performance requirements of wireless communication systems,such as large capacity,high data rate,and small size,furtherly improve,circularly polarized antennas are required to be more broadband,multi-frequency,and miniaturized.In the last decades,researchers have proposed various antenna designs that can be used in mobile satellite communications,WLAN,DBS,RFID,GNSS,space communications,wireless power transmission systems,and next-generation 5G wireless communication applications.However,in terms of bandwidth and volume,the existing designs cannot keep pace with the ever-developing nature of wireless communication systems.Therefore,broadband and multi-frequency circularly polarized antennas are of utmost importance to reduce the size of wireless communication systems and enrich their functions,which will make important contributions to the development of modern technologies.Considering this,we study the methods of using parasitic technology in the design of circularly polarized antennas with single/multi bands.The focus of this work can be summarized in four main aspects as follows:1.The methods of parasitic loading technology are studied to expand the bandwidth of circularly polarized antennas.Firstly,the crossed-dipole antenna is used as the initial structure,which is composed of two orthogonal dipoles connected by a 90° phase shift line.The crossed dipoles can radiate circularly polarized waves,but their bandwidth is relatively narrow.By introducing different forms of parasitic elements between the crossed dipoles,the circularly polarized resonance point can be increased or the working mode of the original point can be improved.In such a way,the working bandwidth of the antenna will be expanded.The parasitic element can be a simple metal patch adding a new resonance point;a grounded parasitic pad improving the original resonance point and also adding a new resonance point;a slot opened on the parasitic patch to produce a circularly polarized new resonance point(at high frequencies without troubling the resonance point generated by the parasitic patch);and a shorted parasitic wall forming a back cavity,thereby improving the circularly polarized radiation performance.Using these methods,three broadband circularly polarized cross-dipole antennas are designed,fabricated,and measured.The measured and simulated results are nearly the same,which validates our theory.2.The design of a circularly-polarized antenna by using a high dielectric constant ceramic material as a parasitic element is studied.The ceramic material,consisting of an L-shaped slot and a metal probe,is excited through the double-feeding method to realize the dual-band dual circular polarization.The high dielectric constant ceramic material makes the dielectric resonator antennas radiate while resonating,which makes them radiating elements.The Lshaped gap not only excites the dielectric resonator but also generates resonance and radiates outward,and hence adds new resonant modes and expands the working bandwidth.The design of the dual-band CP antenna is realized by utilizing the fundamental and higher-order modes of the dielectric resonator and the slot mode.The metal probe and the speciallyshaped dielectric resonator are used to obtain the dual circular polarization.Based on the dual-band dual circularly polarized antenna mentioned above,another wideband dual-sense circularly polarized antenna is proposed based on the rotational symmetry technology to expand the bandwidth.The prototype of the broadband dual-sense circularly-polarized dielectric resonator antenna is fabricated and measured,the results of which prove the correctness of our theory.3.The design of a circularly polarized patch antenna is studied with a perturbation structure.An open-ended and coupled microstrip line is loaded to one side of the rectangular patch to obtain a CP antenna.The way of loading the coupling line can make the rectangular patch antenna to excite two modes,TM01 and TM10,the phase difference of which is 90 °,which refers to the generation of circularly polarized radiation.When the coupling line is placed at different positions of the patch antenna,the phase difference between the two orthogonal modes is either 90 ° or-90 °.Therefore,the polarization of the antenna can be easily controlled,and the left-or right-handed circular polarization can be easily obtained.By combining the two coupling lines at different positions,a dual-band dual-sense circularly polarized antenna is designed.The two prototypes of this CP antenna are fabricated and measured.The measured and simulated results are nearly the same,which validates the theoretical design.It can be used in the antenna designs of dual-band dual-sense circularized polarized wireless communication systems.4.The designs of a series-fed array antenna and a dual-port dual-sense circularly polarized series-fed array antenna based on the loading parasitic slots are studied.The loaded parasitic slots convert the original antenna into a circularly polarized series-fed array antenna.The layout of the series-fed array is more compact and simpler than the parallel-fed array.The dual-port design enables the antenna to radiate at the right-handed circular polarization when Port 1 is excited,and the left-handed circular polarization when Port 2 is excited,thereby meeting the dual circular polarization requirement.