Study Of Wideband And Low-Profile Antenna Based On Hybrid Mode

As an important device for receiving and transmitting electromagnetic waves in wireless communication systems,the performance of antennas directly affects the reliability of mobile communication.With the rapid increase of the number of users in wireless communication systems,the spectrum resources are becoming increasingly tight,and the volume of the communication equipment is also constantly decreasing.Therefore,broadband antennas with low profile are receiving more and more attention and research.This dissertation explores the structure and mechanism of a broadband and low-profile antenna on the basis of traditional microstrip antennas and dipole antennas by combining with the selected topics of scientific research projects.All substrates used are the epoxy fiberglass with a relative permittivity of 4.4 and loss tangent of 0.02.In addition,the dissertation also researches and solves the theoretical,design,and test key technologies of broadband low-profile antennas that are applicable to mobile communication systems.The main research workings are as follows:1.For broadband and low-profile antennas applied to sub-6 GHz mobile communications,a shared aperture broadband antenna with low profile is proposed firstly,which is fed directly from the voltage source with the advantages of simple structure,high gain,a stable pattern,and small cross-polarization.Next,a balun structure is designed to the impedance conversion and single-ended to double-ended.Finally,based on the above research,a shared aperture broadband antenna with low profile is proposed by using balun to feed the dipole directly.When both the narrowband patch mode and the dipole mode are excited by balun at the same time,the impedance bandwidth of the antenna is effectively expanded by overlapping two adjacent narrowband modes.The effects of the length of the dipole,the short axis of the elliptical slot,and the long axis of the elliptical patch on the impedance bandwidth of the proposed antenna are analyzed in detail.A compact prototype with 0.90 ?0 × 0.78?0 × 0.13 ?0 is fabricated and measured.The measured results demonstrate that-10 dB impedance bandwidth is 67.50%,covering 2.75 GHz to 5.45 GHz.The realized peak gain is 8.4 ± 1.10 dBi in the operating band of 3.0 GHz to 5.0 GHz.2.A compact hybrid mode antenna is proposed which is composed of a slotted rectangular patch,a feeding dipole,and a balun structure.Through electromagnetic coupling and slotting,the electrical size of the antenna is reduced and it is beneficial to expand the bandwidth.The effects of the slotted rectangular patch,the feeding dipole,and balun structure on the impedance bandwidth of the proposed antenna are analyzed in detail.The first resonance is determined by the length of the rectangular patch.The second one is affected by the length of the dipole.And the third one is dominated by the length of the rectangular slot.Therefore,three modes are sequentially excited in the operating frequency band of 3.0-5.0 GHz,They are patch mode,dipole mode,and slot mode.A prototype antenna with 0.48 ?0 × 0.31?0 × 0.16 ?0 is fabricated and measured.The measured results demonstrate that-10 dB impedance bandwidth is 56.87%,covering 2.97 GHz to 5.33 GHz.And a stable gain is around 8.00 dBi with 1-dB variation in the operating frequency band of 3.0-5.0 GHz.Moreover,a suitable balun designed is benefit to improve the stability of the radiation pattern.The proposed compact antenna can be an element for micro-base stations in sub-6 GHz communication.3.A compact dual-band dual-polarized antenna is proposed with the crossed dipoles for base station.By introducing a capacitive metal split ring element under the inductive bowtie patch,the matching between the antenna and the feed port is improved due to the capacitive compensation.The additional resonances excited from the parasitic split ring are able to effectively expand the bandwidth of the proposed antenna.And a shared aperture design with integration is achieved.The measured impedance bandwidths are under the standard of VSWR<1.5.The low frequency band covers 2.32 GHz to 3.72 GHz while the high frequency band covers 4.76 GHz to 5.20 GHz.And the stable radiation patterns are achieved in both frequency bands with good far-field radiation characteristics.The operating frequency bands of the proposed antenna can cover the latest frequency band of 2515 MHz-2675 MHz,3400 MHz-3600 MHz,and 4800 MHz-5000 MHz divided by the three maj or communication operators.