The Design And Research Of The Novel Ultra-wideband Filter

With the development of the ultra-wideband technology, the ultra-wideband filteras one of the core components at UWB system has caused a lot of attraction all over theworld. Although there are a lot of researches on the ultra-wideband microstrip filter, ithas so many disadvantages: the band-width is not wide enough, insertion loss is large,the structure is not stable enough, the rejection of stopband is poor, and power capacityis low. This paper prepares to design some kinds of ultra-wideband filters, Aim for themaximum bandwidth is more than150%and have good experimental results. Thispaper firstly use the theoretical properties of ridge waveguide which has widebandwidth when work with single-mode, we designed a ultra wideband bandpass filterwith the band from3.1GHz to10.6GHz, successfully to control the parasitic passbandbeyond18GHz. And then put forward a kind of ultra-wideband coaxial connector to theridge waveguide(applied for patent), using this connector we designed three UWBhigh-pass filters whose largest bandwidth expand to more than150%, to achieve highrejection steep outside the band(applied for patent). Finally we completed the design ofsuspended stripline UWB filters, the insertion loss is less than1dB, and it completelyaccords with the characteristics that suspended stripline has a low insertion loss. Allultra-wideband filters were processed and measured, the final test results basically meetthe expected index requirements.The main content of this thesis are as follows:1. It gives a brief introduction of the rationales and index parameters of microwavefilter in terms of the prototype of low-pass filter.2. It analyzed the theoretical features of ridge waveguide. And inspired by the factthat the bandwidth of ridge waveguide can reach several times of its octave, the paperproposed a strong coupling structure which connected the metal ridges among resonantcavities and then analyzed the structure. Finally it designed a UWB bandpass filterusing the coupling structure. The bandpass filter ranged from3.1-10.6GHZ with areturn loss of-10db, an insertion loss of-1.5db and a parasitic passband of18GHZ.3. It gives the design of a kind of coaxial connector to the ridge waveguide whose maximum relative bandwidth is more than150%. Using this connector we designedthree new ultra-wideband filters. One kind is a Ultra-wideband filter with band of3-13GHz whose return loss is-10dB, insertion loss is-2dB, its rejection of stopband is-60dB at the frequency of2GHz; the another kind filter with band of2.5-18GHz, itsreturn loss is-10dB, insertion loss is-2dB, the rejection of stopband is-55dB at thefrequency of2GHz.4. Using the advantage of suspended stripline structure with low insertion loss, wedesigned two kinds of suspended stripline ultra-wideband filter, whose passband are3-18.5GHz and4-19.5GHz, the return loss is more than10dB, and insertion loss is lessthan0.5dB. Moreover, this UWB filter have transmission zero in the stopband.5. Finally, it gives the summary and analysis of the thesis.