Research On Filtering Antennas For Off-Body Communications

In recent years,the wearable devices have gradually become a research hotspot in the sci-entific community.The technologies in off-body communications have been widely applied in many fields,such as entertainment,sport,and healthcare.Now,the antennas for off-body com-munications are limited due to some problems,such as big size,low integration and mono function.The filtering antenna with the performance of radiation and filtering,integrating the antenna with filter,could achieve the multi functions and realize miniaturization.Therefore,it has great value to design filtering antenna with excellent performances for off-body communi-cations.This work was supported in part by the National Natural Science Foundation of China(No.61372008),and in part by the Science and Technology Planning Projects of Guangdong Prov-ince(No.2014A010103014,No.2015B010101006).In this dissertation,three sets of novel filtering antennas based on the theoretical knowledge of filter and antenna are proposed.They can achieve excellent radiation and filtering performances without extra filter circuit.The main works of this dissertation are as followed:(1)Single-band filtering antenna integrated with artificial magnetic conductor:This part mainly presents a single-band filtering antenna.The proposed antenna with coupled feed and slotted patch obtains a band-pass filtering response through two radiation zeros located in two sides of passband.By equiping the artificial magnetic conductor in the bottom of the proposed antenna,the impedance of the antenna could be adjusted,alleviating the impact on the human body.The dimensions of the proposed antenna are 40×22×2.826 mm~3.The impedance bandwidth is 5.55–5.95 GHz.(2)Dual-band filtering antenna without extra filter circuit:In this part,a single-layer die-lectric substrate is adopted to reduce the profile of the antenna.It is found that slotting on the patch or ground could introduce the band-stop filtering response.Two pairs of rectangular nar-row slots and a pair of open rings are added to the radiation patch,changing the electric field mode of the proposed antenna.This makes the currents at some specific frequency point coun-teract each other,resulting in dual-band fitltering response with three radiation zeros.A full ground is equipped to alleviate the radiation on the human body.Dual bands enable the device to work in two different modes.The final sizes of the proposed antenna are 41.5×33.9×1.524mm~3.The impedance bandwidths are 4.95–5.24 GHz and 5.78–5.84 GHz,respectively.The characteristics of low profile and good filtering are achieved.(3)Wide stopband microstrip filtering antenna with compact size:In this part,the prob-lems of relatively large size and narrow stopband in the previous two types of antenna are ad-dressed.The wide stopband can filter out more useless signals.Because of the bandgap charac-teristic of split-ring resonator,two radiation zeros are generated by adding a pair of split-ring resonators in both sides of the feed microstrip line.The additional two radiation zeros are achieved by etching narrow slots and open rings.The proposed antenna with four radiation zeros can realize the merit characteristics of band-pass filtering and stopband suppressing.The antenna adopts edge feed and compact structure to reduce the profile and size of antenna.The final sizes of the proposed antenna are 24.5×24.5×1.524 mm~3.The impedance bandwidth is4.9–5.5 GHz.The stopband gains at low frequencies(3.6–4.6 GHz)is less than–15 dBi.The stopband gains at upper frequencies(5.8–6.4 GHz)is less than–20 dBi.A compact filtering antenna with wide stopband is realized by adopting single layer dielectric substrate and sym-metrical structure.