Study On Circularly Polarized Non-uniform Circular Loop Antenna Under Even-mode Resonance

This thesis is devoted to the research of loop antenna under even-mode resonance.Theoretic analysis of uniform and non-uniform loops is performed to obtain the fundamental even-mode and third-order even-mode of non-uniform loop antenna,and even far-field theoretical formulas for high order even-modes.A design method of non-uniform circularly polarized(CP)loop antenna is presented,and propose an improved design of a dual-band CP square loop antenna under even-mode resonance.The main content of this thesis includes:1.According to classic theories of loop antenna,uniform loop antenna with uniform current distribution and cosine current distribution is analyzed.The far-field theoretical formulas of the fundamental even-mode and third-order even-mode of the non-uniform loop antenna are derived.The presented analysis method can also be applied to other high order even-modes.2.According to match the natural boundary condition to determine the excitation method,use the software HFSS for simulation analysis,then optimize the antenna structures and parameters,design a directional non-uniform CP loop antenna,and finally make the antenna object.The measured results prove the antenna radiates right-handed CP(RHCP)waves in +z direction,and have impedance bandwidth of 9.72% and axial ratio(AR)bandwidth of 6.86%.3.An improved design of a dual-band CP square loop antenna under even-mode resonance is presented,fully excite the third-order even-mode by adjusting four L-shaped tuning stubs,and antenna is fed by a pair of orthogonal dipole launcher with fork-like stubs,so that fundamental mode and third-order mode have same CP performance.Then optimize the antenna structures and parameters,make the antenna object.The measured results prove the antenna radiates RHCP waves in +z direction both the fundamental mode and third-order mode,the fundamental mode has impedance bandwidth of 13.8% and AR bandwidth of 1.3%,and third-order mode has impedance bandwidth of 16.7% and AR bandwidth of 1.2%.