Design of differentially-driven chip antenna

Abstract

In this thesis, a differentially driven microstrip antenna using an aperture coupled feed technique is proposed. A differential antenna is preferred because of lower noise; lower susceptibility to interference and is more suitable for high level integration or single chip solution of radio systems. Thus, the use of lossy balun which is often used to connect single-ended antenna to RF circuits can be eliminated.

First, the design formulas for single ended microstrip antenna have been examined to design for differentially microstrip antenna using the aperture coupled feed techniques. It was found that the patch width of the differential antenna structure has to be widened to excite the fundamental mode〖 TM〗_01 and the patch length needs to be shortened to achieve the resonant frequency of 2GHz. The shift of the resonant frequency is due to the induced inductance caused by the slots in the ground plane. The research works presented in this thesis conclude that the excess reactance of the differentially driven aperture coupled antenna can be eliminated by tuning the stub length; The required resistance of the antenna structure can be adjusted by varying the aperture length; the occurrence of the resonance depends on the electrical separation which is defined as the ratio of the distance between the two driving points to the free space wavelength λ_0. When the driving points are located far from one another ξ/λ_0 >0.1 for an electrically thin substrate, resonance occurs. When the driving points are located near to each other ξ/λ_0 <0.1, there will be no resonance.