Research On Differential Feeding Broadband Antennas

With the rapid development of 5G communication technology,antenna needs to cover more frequency bands and reach the broadband effect,which brings severe challenges to the antenna design.Also,the size of the whole communication link will be increased by cascading the antenna and filter through the microstrip line,and the impedance matching might be introduced.Consequently,it is a great solution to design the filtering antenna by integrating the filter and antenna into one microwave component.In this paper,based on the differential feeding technology and the principle of multimode resonance excited by slot resonator,the original 8% maximum fractional bandwidth(FBW)of the planar inverted-F antenna(PIFA)is broadened to a broadband filtering PIFA which can work at2.1?5.1GHz.The proposed filtering antenna has low differential-mode standing wave,high commonmode suppression,symmetrical and stable radiation pattern characteristics,high gain,and the filtering effect is obvious.The main contents of this work is composed of the following aspects:Firstly,this paper has introduced the recent research status of the differential broadband antennas at China and abroad,systematically summarized the theoretical knowledge and parameter indicators of PIFAs.Then,a wireless local area network(WLAN)antenna which center frequencies are at2.4GHz and 5.8GHz has been proposed.Compared with the other WLAN antennas,this antenna has smaller size,simpler process,and work stably at dual-bands of 2.4/5.8GHz.Secondly,a broadband differential PIFA with the center frequency of 3.7GHz is designed by differential feeding technology.After S-parameters tests,the results are shown that the differentialmode standing-wave ratio of the differential PIFA at 2?5.4GHz is less than 1.7,and the impedance bandwidth is greater than 3.4GHz,which achieve the requirement of wide frequency band.In the meantime,the in-band gains of this antenna are greater than 5dBi,and the efficiencies are greater than 95%.In addition,a differential band-pass filter(BPF)is designed with the principle of multimode resonant modes excited by slot resonator,which has excellent performance of broadband,low differential-mode loss,high common-mode suppression and so on.Thirdly,in order to realize the filtering effect of the antenna,the broadband differential PIFA and the differential BPF are combined into a microwave device.The actual test shows that the frequency range of the broadband filtering differential PIFA is 2.1?5.1GHz,the impedance bandwidth is 3GHz,the fractional bandwidth is more than 80%,the in-band differential-mode standing-wave ratio is less than 1.8,and the common-mode rejection ratio is greater than-1.83 dB.Finally,the peak gain of the proposed filtering PIFA is greater than 4dBi and the efficiency is greater than 90%.Above all,the peak gains of the filtering PIFA are greater than 5dBi and the efficiencies are greater than 98% above the 3.5GHz band.