Research And Design Of Novel Dipole Antennas

Dipole antennas have the advantages of small size,low cost,light weight,and ease of forming an array,and have attracted wide attention in recent years.Moreover,circularly-polarized(CP)antennas have been widely used in wireless communication systems such as global positioning systems and satellite communications due to their obvious advantages of suppressing the Faraday rotation effect.Therefore,the CP dipole antenna has great research value.On the other hand,dual-polarized antennas have been more and more popular in base station applications because they can suppress multipath interference and increase channel capacity.With the rapid development of wireless communication technology,the miniaturization and compactness of mobile communication systems have been a new trend.The contradiction between the miniaturization and wideband of the antenna,the contradiction between the miniaturization of the MIMO antenna and high isolation between antenna elements,and the contradiction between the high integration and high performance of the antenna and other devices have become the difficult problems in antenna designs.To tackle these problems,four novel circularly polarized/dual-polarized dipole antennas are designed based on the topic of the dipole antenna.The main research contents of this paper are as follows.Firstly,a low-profile wideband CP crossed-dipole antenna has been proposed.Eight parasitic elements are located on the top and bottom surfaces of the same substrate printing the crossed dipoles to reduce the profile of the antenna and increase the bandwidth of the antenna in this design.Each parasitic element consists of a horizontal patch and a vertical shorting pin.The four parasitic shorted patches located on the bottom surface of the dielectric substrate can increase the CP bandwidth of the antenna and reduce the profile of the antenna,while the four parasitic shorted patches located on the top surface of the dielectric substrate can further increase the AR bandwidth of the antenna and improve the gain of the antenna.Therefore,the proposed antenna has a profile of as low as 0.067?₀,a-10 d B impedance bandwidth of 61.8%,a 3 d B AR bandwidth of 51.6%,and a gain fluctuation of 1.2 d B within the overlapping passband.Compared with the reported wideband CP crossed-dipole antennas,the proposed design has the lowest profile and the competitive CP bandwidth.Secondly,a CP crossed-dipole MIMO antenna with high port isolation level is proposed.By introducing a single shorting pin between two identical CP crossed-dipole antennas,the dip with minimum|S₂₁|at the high frequency band shifts downwards to the desired working frequency band of the antenna,and therefore,the lowest mutual coupling level of the two antennas reaches about–26 d B in this design.Moreover,the mutual coupling level of the two CP crossed-dipole MIMO antennas is lower than–20 d B within the CP passband of 13.2%.Compared with the reported CP MIMO antennas,the decoupling technology of the proposed design is the simplest,and it achieves a higher port isolation level within a wider CP bandwidth.Moreover,the shorting pin neither increases the back radiation of the antenna nor increases the profile of the antenna.Thirdly,a single-layer low-profile CP filtering patch dipole antenna is proposed.One square feeding loop and four L-shaped patches located around the loop are used to generate CP radiation in this design.In addition,simple parasitic elements,including four thin microstrip stubs,four shorting pins,and two identical U-shaped slots,are introduced into the antenna to realize the bandpass filtering function.Therefore,the antenna achieves a CP bandwidth of 4.1%with a profile of as low as 0.02?₀,and the antenna gain reaches 8.3 d Bic.Moreover,the antenna obtains a relatively sharp roll-off rate at the edge of the passband and a high out-of-band suppression level of higher than 20 d B.Compared with the previous designs,it can be seen that the proposed CP filtering antenna achieves a good filtering response without using any extra filtering circuit.Therefore,the additional loss of the external filter is eliminated,and the antenna has a higher gain.Also,the entire antenna is designed on a single-layer substrate,and it has the lowest profile.Finally,a wideband dual-polarized dipole antenna is proposed.Four folded metal plates are introduced on the ground plane of the dual-polarized dipole antenna to increase the bandwidth of the antenna in this design.Specifically,using the coupling effect between the folded metal plate and the adjacent dipoles,the antenna generates an additional resonant mode beside the original passband,substantially enhancing the impedance bandwidth from 30%to about 92%.Furthermore,the isolation level between the two ports of the antenna within the entire impedance passband is more than 20 d B,and the average gain is about 6.2 d B.Compared with the published designs,the present antenna simultaneously has the lowest profile and widest usable impedance bandwidth.