Research On Broadband Omnidirectional Microstrip Antenna Based On UWB Positioning System

In view of the obstruction of indoor GPS signals and the precise positioning of out-door complex environments,ultra-wideband（UWB）positioning technology using narrow pulses as the information carrier has become one of the mainstream solutions.As the key device in UWB positioning systems,the antenna is an important guarantee in the undis-torted transmission of the signal.Traditional time-domain antennas all have huge lim-itations in the increasingly demanding installation environment.Broadband microstrip antennas have the advantage of low profile and are a good alternative.This thesis will firstly use the cavity theory to describe and discuss the circular microstrip antenna with circularly symmetrical distribution of short-circuit vias,obtain the factors affecting the res-onant frequency of this type of antenna by modifying the boundary conditions,and then design three microstrip antennas that meet the time domain signal transmission based on this theory.The main contents are as follows.1.Line Polarized broadband antenna design:According to the broadband require-ments for pulsed UWB technology applications,the TM₀₁and TM₀₂modes of the circular microstrip antenna,and the additional anti-resonance mode are simultaneously excited through the tapered feed matching technology,a linearly polarized broadband omnidi-rectional microstrip antenna is designed.Its tested impedance bandwidth is 44.1%,the waveform fidelity is 96.2%,and the group delay fluctuation is less than 0.5ns.Simulation and test results verify the feasibility of propagating time domain signals.2.Circularly polarized broadband antenna design:For the problem of anti-multipath interference in complex environments,based on the TM₀₁and TM₀₂modes of the afore-mentioned linearly polarized antennas,multiple sickle-shaped branches are introduced on the antenna floor to generate an orthogonal electric field,and a circularly polarized broad-band omnidirectional microstrip antenna is designed.The tested impedance bandwidth is46.8%,the axial ratio bandwidth is 36.7%,the available coincidence bandwidth is 36.7%,and the waveform fidelity is 97.9%and 97.4%under direct and multipath conditions re-spectively.The results show that the circularly polarised antenna has the ability to resist multipath.3.Design of gain-stabilized antenna:According to the requirement of undistorted signal transmission,a gain-stabilized broadband omnidirectional antenna is designed based on the line polarized antenna,using patch folding technology to realize broadband match-ing.The simulated impedance bandwidth is 62%,and t is far-field phase is linear in fre-quency function,the gain fluctuates less than 0.5d B within the working frequency band6-9GHz.Compared with the simulated transmitting waveform,signals radiated by the antenna have a fidelity of over 99%.The above three antennas are based on the theoretical analysis of cavity and feed matching techniques,which provides an effective way for the design of broadband omni-directional circular microstrip antennas.