Research And Design Of High Selective Filters And Filtering Antennas

With the continuous upgrading and diversification of electronic devices,modern wireless systems are placing increasingly high demands on device performance.The increased number of devices and integration lead to subsequent pressure on size and cost.Filters and antennas,as two important devices in the RF front-end,have been a hot topic of research.Firstly,filters have a wide range of applications in electronic devices and have an important impact on the realization of system performance.In addition,in order to obtain higher out-of-band rejection performance,the antennas are often required to have good frequency selection performance.Therefore,filters and antennas are also often cascaded in engineering designs.However,this method will lead to large size and high loss problems for some applications.Moreover,some applications have very strict requirements for out-of-band rejection,so it is difficult to obtain satisfactory out-of-band rejection by cascading the filter and the antenna only.The proposed filter antenna is a good solution to these problems.It integrates the antennas and filters design,so that it has both radiation and filtering functions,which can be applied to the filter and antenna cascade system to meet the strict out-of-band rejection requirements.Therefore,the research and design of highly selective filters and filtering antennas is very important.The work of this paper is as follows:1.An ultra-wide stopband compact S-band bandpass filter is proposed.The filter consists of three main components:a cross-shaped resonator,parallel coupled lines,and the metal ground etched with a defective ground structures（DGS）.The three capacitive open stubs in the middle of the filter act as resonators,and out-of-band resonances are suppressed by etching a rectangular slot in the middle open stub.The parallel coupled lines on both sides are mainly used to improve the passband and roll-off rate,and the DGS structures in the metal ground can further optimize the stopband performance.The proposed bandpass filter has the advantages of compact structure,low insertion loss and high stopband width.Process measurements show the 3-d B operating band is 1.80-4.03 GHz（76.5%relative bandwidth）,with better than 20 d B rejection in the upper stopband up to 20 GHz（6.33 f₀）and the upper stopband roll-off rate is 76.59 d B/GHz.2.A single-band bandpass filter and a dual-band bandpass filter based on the SSPP structure are designed respectively.Firstly,an SSPP unit structure based on parallel-coupled open stubs is designed.This structure has good dispersion characteristics compared to the conventional rectangular SSPP unit of the same size,and the asymptotic frequency is reduced from 2.46 GHz to 2.07 GHz.A single-band bandpass filter and a dual-band bandpass filter are designed based on this structure,both of which have the advantages of low insertion loss,high out-of-band suppression performance and simple structure.The single-band bandpass filter has a 3-d B operating band of 5.35-8.68 GHz（relative bandwidth of 47.4%）.The average insertion loss in the passband is only 0.07 d B,and the roll-off rates in the upper and lower resistance bands are 48.46 d B/GHz and 45 d B/GHz,respectively.The dual-band bandpass filter has the 3-d B operate bands of 4.54-7.40 GHz（47.9%relative bandwidth）and9.36-12.01 GHz（24.8%relative bandwidth）.The average insertion loss in the passband is0.08 d B and 0.14 d B respectively,with roll-off rates of 69.87 d B/GHz（upper resistance band）and 48.50 d B/GHz（lower resistance band）in the lower passband.The roll-off rates in the higher passband are 30.09 d B/GHz（upper resistance band）and 90.14 d B/GHz（lower resistance band）.3.A highly selective filtering antenna based on a Spoof surface plasmon Polaritons（SSPP）structure is proposed.Firstly,a novel SSPP unit structure based on bending lines structure is designed,which reduces the asymptotic frequency from 11.91 GHz to 4.04 GHz compared to a conventional rectangular unit of the same size,which means that the electrical size of the proposed SSPP cell can be reduced by 2/3.The filtering effect of the antenna can be achieved without the additional resonator structures.Finally,out-of-band resonances suppression are achieved by the rectangular slots etched into the SSPP transmission line.In addition,the radiation nulls can be adjusted by changing the critical dimensions of the SSPP unit.Measured results show that the operates band of the antenna is 2.130-2.606 GHz with in-band average gain of 8.89 d Bi and a peak gain of 10.55 d Bi.The suppression level exceeds23.708 d B in the band of 3.2-7.4 GHz and the upper stopband roll-off rate reaches 84.78dB/GHz.