Study And Design On Broadband Passives In Wireless Communication System

With the development of wireless communications, the miniaturized and broadband passive components for the RF front-end are requested. The substrate integrated waveguide filter are widely studied because of their own advantage, such as, light weight, small volumn and easy integrated with other component Also, the circularly polarized (CP) antenna has been widely used in satellite communications and pulse radars, in which wider impedance and axial ratio (AR) bandwidth are required. In this thesis, a kind of compact and broadband filter based on SIFW is first discussed in this paper. Then a kind of broadband circularly polarized slot antenna is proposed. The main content of this paper is mainly divided into three sections:Firstly, the statuses of the substrate integrated waveguide filter and circularly polarized antenna in wireless communications are presented. Then several important parameters and numerics algorithm for filter and antenna are introduced.Secondly, a kind of compact bandpass filter based on Substrate integrated folded waveguide is proposed and its simulation result is given. In order to improve the band rejection at the low passband, a cross coupled structure is introduced and two transmission zero in the low passband are obtained. Also, a pair of CSRR slot is etched on the top and bottom microstrip to improve the characteristics in the high of the passband. The simulation result shows that the proposed filter can operate at7.1GHz, the relative bandwidth is about47%, the return loss in the passband is better than-15dB, and the insertion loss in the passband is less than0.7dB.At last, a broadband circularly-polarized slot antenna is proposed. The CP radiation of the slot antenna is excited by the proximity coupling of a microstrip line. To obtain a broad CP bandwidth, three CP modes contained in the CP band are excited. At the same time, the tapered feeding structure is use to improve the impedance characteristics of the input port. The results show that the proposed antenna can provide a CP operating bandwidth of56%(3.17GHz-5.65GHz) within an impedance bandwidth of64%(2.96GHz-5.75GHz). The peak gain of antenna is3.5dB.