Study On Method Of Diversity Reception With Wearable Planar Circularly Polarized Antennas

With the increasing development of Internet of Things,the human-centered wireless communication system will become an important part of mobile communication system,all kinds of portable,wearable,implantable wireless communication system will be gradually integrated into people's life.In human-centered wireless communication systems,the characteristics of wearable antenna will directly affect the performance of the whole system.Since the future wireless communication system will evolve into more than 6 GHz-band,propagation loss in high frequency-band will be significantly increased and multipath fading is more serious,so the wearable antenna diversity will be a key strategy to lower loss,overcome the fading and improve capacity and reliability of the system.So,improving the performance of diversity system is the primary factor to reduce the correlation between the diversity antenna unit.A wearable diversity antenna system realizing by a kind of planar endfire circularly polarized(CP)antenna should be effective and beneficial to solve the aforementioned problems.By using the polarization isolation characteristics of a pair of circularly polarized antennas,correlation between diversity antennas can be reduced effectively.The main content of this thesis is organized as follows:1.Design approach of the basic diversity antenna element is developed at first.Based on the theory of basic magnetic and electrical dipoles,an equivalent source model of the antenna is established.The radiation behavior is then revealed,and a set of design criteria is presented by the closed formulas deducing from the far fields of the antenna.2.The parameters of the planar endfire CP antenna are analyzed and optimized by using HFSS.The prototypes of the antenna are fabricated and measured by Agilent's 8720 ET vector network analyzer and Satimo Starlab near field antenna measurement systems.The simulated and measured results agree well with each other.The reflection coefficient of the antenna is lower than-10 dB,and the axial ratio is smaller than 3dB within 2.40-2.56 GHz.3.The designed antennas are re-designed at the 5.8 GHz radio frequency identification(RFID)band.A pair of antennas are worn on the shoulders of human body as “epaulets”.An indoor security environment is chosen as an application scenario to verify the actual transmission characteristics of the antenna system.For comparisons,different combinations of wearable antennas are employed in the diversity antenna systems.The transmission bit-error-ratio(BER)curves of different wearable diversity antenna combinations are emulated and compared.It is found that the wearable diversity antenna system composed by a pair of differentially combined CP antennas exhibits the best performance.