Compact circularly polarized slot-ring antenna and microstrip bandpass filter using triangular open-loop resonators

摘要

In this thesis two different research topics are undertaken, both in the area of compactRF/microwave circuits design. The first topic involves the design of a compact circularlypolarized (CP) slot-ring antenna. A study of several compact CP microstrip and slotlineantennas reported in the past has been carried out. In this research, a method of reducingthe size of a printed slot-ring antenna is proposed. The reduction in size is achieved byintroducing meandered-slot sections in the ring. Circular polarization is achieved byintroducing an asymmetry, also a meandered-slot section, and feeding the antenna at anangle of 45o from the asymmetry using a microstrip feed line. The minimum axial ratioof 0.4 dB is obtained at 2.46 GHz, which is the operating frequency of the antenna. Thesize of the proposed antenna is reduced by about 50% compared to a conventional CPslot-ring antenna and it displays a CP bandwidth of about 2.5%. The simulated andmeasured results are presented, and they are in good agreement. The small size of theantenna makes it very suitable for use in modern RF/microwave wireless systems whichrequire compact, low cost, and high performance circuits. Moreover, its CP behaviormakes it more attractive for applications such as satellite communications. The second topic in the thesis involves the design of a compact microstrip bandpassfilter using triangular open-loop resonators. A new compact three-pole microstripbandpass filter using four triangular open-loop resonators is presented. A fourthresonator is placed to provide cross-coupling in the structure which gives a better skirtrejection. The measured pass-band center frequency is 2.85 GHz. The filter demonstratesabout 7% bandwidth with insertion loss of less than 1 dB in the passband, a return lossof greater than 15 dB and out-of-band rejection of greater than 30 dB. The simulatedand measured results are in good agreement. The proposed filter is very attractive for usein modern wireless systems which require bandpass filters having compact size, lowinsertion loss, high selectivity, and good out-of-band rejection.