Design Of Terminal Antenna Based On Multi-mode Resonator

In recent years,with the rapid development of wireless communication system,the miniaturized and multifunctional development trend of mobile terminal put forward higher requirements for RF front-end.The antenna as an important component of communication system needs to be miniaturized,integrated,multi-frequency and broadband.Using the multi-mode resonator,the new resonant mode can be excited without increasing the size of the original antenna.In addition,based on the analysis of the resonance characteristics of the multi-mode resonator,the multi-band filtering antenna can be designed by integrating the multi-mode resonator and the multi-band antenna.The multi-band filtering antenna can not only realize filtering and radiation characteristics on multiple frequency bands,but also realize miniaturization and integration of RF front-end.Firstly,based on the resonance principle of multi-mode resonator,a quad-band mobile phone antenna is designed by using the coupling between multi-modes,the slotting and loading branch on the ground in this paper.The antenna consists of a tri-mode T-shape monopole,a slot etched on the ground and an open-ended branch loaded on the ground.The T-shape monopole consists of a long branch and a short branch.The lengths of the long and short branches are about 0.25-wavelength at 0.9 GHz and 1.85 GHz,respectively,making the T-shape monopole resonate at 0.9 GHz and 1.85 GHz.Based on the dual-mode T-shape monopole,a new resonant mode at 2.4 GHz is excited by bending the long branch of the T-shape monopole,making the T-shape monopole resonate at 0.9 GHz,1.85 GHz and 2.4 GHz.By expanding the short branch of the T-shape monopole,the mid frequency and upper frequency are pulled close to cover a wide band(1.7~ 2.71 GHz).By etching a slot on the ground,the impedance of the antenna at 0.9 GHz can be matched,covering 0.82-0.96 GHz.To further broaden the low frequency band,a new resonant mode was introduced at 0.73 GHz by loading an open-ended branch on the ground.Finally,the antenna successfully covers LTE 700(0.69~0.78 GHz),GSM 850(0.82~0.89 GHz),GSM 900(0.88~0.96 GHz),DCS 1800(1.71~1.88 GHz),PCS 1900(1.85~1.99 GHz),UMTS(1.9~2.17 GHz),LTE 2300(2.3~2.4 GHz)and LTE 2500(2.5~2.69 GHz).The proposed antenna is fabricated and measured.The consistency between the measured and simulated results indicates that the proposed antenna is available for mobile phone applications.Secondly,based on the synthesis design method of filter,a tri-band filtering antenna working at WLAN 2.45GHz/5.2GHz and Wi-Max is designed by adopting the design method of replacing the last resonator of filter with an antenna.This antenna consists of a tri-mode stub-loaded resonator,a ?-shape parallel coupled line and a tri-band monopole.The design process of the tri-band filtering antenna can be divided into three steps: First,according to the design method of the coupling band-pass filter,a second-order tri-band filter working in the selected frequency band is designed by using the tri-mode stub-loaded resonator.Second,a simple tri-band monopole working in the selected frequency band is designed.Third,by using appropriate coupling structure,the tri-band monopole can replace the last resonator of the second-order tri-band filter,realizing the integration of the antenna and the filter.The tri-band filtering antenna is simulated and fabricated,the measured results agree well with the simulations.The tri-band filtering antenna has a compact structure,exhibiting good frequency selectivity and out-of-band rejection in the three frequency bands.