Research And Design On Wideband Filter And Vivaldi Antenna

With the rapid development of wireless communications technique,especially in the fields of microwave and millimeter-wave,the demands of the passive components used in all kinds of communication systems are higher and higher.Interest in ultra-wideband(UWB)technologies is increasing because of its unique advantages including wideband operational bandwidth,great secrecy performance,high transmission rate,and so on.Ultra-wideband bandpass filters and antennas as key passive components for ultra-wideband systems restrict its communication quality.Therefore,it is extremely urgent and important that we start to research ultra-wideband passive components(UWB bandpass filters and UWB antennas).In this thesis,some key passive components used in UWB communication systems have been studied,and this thesis mainly contains four parts as follows:Firstly,the research status of ultra-wideband bandpass filter(BPF)and broadband antenna applied in the UWB wireless communication systems are presented.And then,some important parameters for filter and antenna are introduced in this thesis.Secondly,several filters using hybrid CPW and microstrip structures are proposed.In order to improve the selectivity,the interdigital coupled-line and split ring resonator are used.Moreover,a filter with a notched band at 8.2 GHz with a maximum rejection loss of 42 dB is achieved by introducing a coupling T-shaped short stub.Then,a novel defected microstrip structure resonator(DMSR)is proposed and analyzed.Moreover,an UWB BPF is designed based on the DMSR.In order to improve the selectivity,a modified UWB BPF based on the proposed DMSR is designed and fabricated.The measured results show that the proposed filter achieves a 3-dB fractional bandwidth of 133% over the frequency range of 2.3 GHz to 11.5 GHz.In addition,the return loss is better than 14 dB from 2.7 GHz to 11.3 GHz.And the insertion loss is less than 0.4 dB around the central frequency.Besides,several UWB bandpass filters with compact size are presented in this thesis.Finally,a modified antipodal Vivaldi antenna and two novel balanced antipodal Vivaldi antennas are designed.The antenna gain and beam tilts are enhanced remarkably by inserting a compounded elliptical metal patch called director in the middle of the antenna aperture.The measured results show that antenna gain of the proposed antipodal Vivaldi antenna > 10 dBi for frequencies more than 7 GHz and > 15 dBi over the frequency range of 17 to 30 GHz.The proposed two balanced antipodal Vivaldi antennas exhibit good performances such as satisfactory endfire characteristic,low cross-polarization,compact size,relatively high gain and extremely wide operational bandwidth(2 to more than 40 GHz),which make them suitable for applications in phased array,UWB system and target RCS imaging,etc.