Design Of Broadband/Dual-Band Dual-Sense Circularly Polarized Microstrip Antennas

Antenna, as a key component of the wireless radio systems, has critical influenceson the performance of the system. For the purpose of flexible orientation of both thetransmitting and receiving antennas without causing a severe polarization mismatch,the circularly polarized (CP) antennas have aroused wide attention in the fields of radar,wireless communication, and navigational systems.In this thesis the CP microstrip slot antennas fed by coplanar waveguide (CPW)and microstrip patch antenna for wireless communication systems are addressed. TheHFSS software is utilized to analyze and optimize the antenna parameters. Antennaprototypes based on the design dimensions are fabricated and measured. Measuredresults indicate that excellent CP waves can be achieved. They are found to possess theproperties of compact, broadband, and dual-band dual-sense CP radiation, respectively.Firstly, a CP microstrip slot antenna with a compact size of0.328λ×0.328λ×0.004λ is presented. As slight perturbation segments for generating CP the L-shapedslots placed around two opposite corners of the square slot are centrosymmetric.Secondly, the broadband CP slot antenna is presented. As the perturbationsegments for generating CP, a square tuning stub is deposited at the end of thehorizontal part of the inverted-L CPW signal strip. In addition, by adjusting the lengthof the pair of I-shaped strips, the3dB AR bandwidth can also be significantlyenhanced. The3dB AR bandwidth enclosed by the VSWR≤2impedance band can beup to45%(1.65-2.64GHz).Thirdly, the dual-band slot antenna with a C-shaped grounded strip is proposedfor dual-sense CP radiation. The lower band circular polarization can be achieved bythe perturbation of L-shaped slots placed around two opposite corners of the squareslot. The C-shaped grounded strip on the right hand side can offer a current path for theupper band, thus resulting in dual-band operation. The antenna possesses the measured10dB return loss impedance bandwidth of106.9%(1.01-3.33GHz). The measured3dBAR bandwidths for the lower and upper bands can be up to32.35%(1.41-1.96GHz)and5.6%(2.45-2.59GHz), respectively.Finally, For the application in high-capacity wireless communications andpolarization diversity system, this dissertation makes insight to the design of microstrippatch antenna with broadband dual-sense CP radiation. The proposed antenna, fed by port1, radiates a LHCP wave. The3dB AR bandwidth totally enclosed by S11≤-10dB impedance band can be up to53%. It can also be obtained that the proposedantenna fed by port2provides RHCP radiation characteristic. The3dB AR bandwidthtotally enclosed by S22≤-10dB impedance band can be up to51.7%. Its propertiesmake the antenna suitable for polarization diversity operation.