A windmill-shaped loop antenna for polarization diversity

Over the last several decades, the small loop antenna has been studied by many researchers. It has been used as paging antenna, AM receiving antenna and probe for measuring the EM field. These days, it is also studied to implement polarization diversity which means that both antennas have the orthogonal polarization, same radiation pattern and high polarization purity. In general, the small loop antenna has a total wire length of less than one-tenth of wavelength and uniform current distribution. A size restriction of the small loop antenna causes its low efficiency. Therefore, techniques such as extra matching circuit and multi-turn were used to improve performance. However, the matching circuit which uses the lumped capacitor and resistor increases loss of the antenna. Also, conventional small loop antennas were mainly implemented at low frequency due to the size restriction. In this paper, a windmill-shaped small loop antenna is proposed at 2.6 GHz. It has a total length which is several times greater than that of the conventional one and uniform current distribution and it needs no extra matching circuit. A return loss and a radiation pattern of the proposed antenna are investigated. Moreover, it is confirmed that it can be used as one of the duality antennas to implement polarization diversity. All simulation result are verified by CST MWS (Ver 5.0).