Design And Research On The Micro-strip Filters

In the wireless communication system, FR filters with the selection of frequency band and channel, can filter harmonic and inhibit the stray. The performance has a direct effect on the whole performance index of the communication system. With the development of the technology, radio frequency filters with the requirement of high performance, small volume and convenient integration has become the trend.Filters with the Micro-strip line construction has been widely used due to its characteristic of small size and easy processing.The traditional stepped impedance filter has the feature of simple construction and easy to achieve. But its large volume, narrow stop band, and not restraining the higher harmonic effectively, so its application has been limited in some fields. This thesis has adopted the two common radio frequency designing system--HFSS (High Frequency Structure Simulator) and ADS (Advanced Design System), and has combined the two of them at the same time. By using the electromagnetic field and the method of circuit simulation, it has analyzed the DGS(Defected Ground Structure) and the scattering characteristics of semi-circular Stepped impedance resonator unit. Besides, it has established general parameter equivalent circuit model of DGS unit and a semi-circular stepped impedance unit. On the basis of this, it has designed a kind of micro-strip low-pass filter with the features of DGS unit combine stepped impedance resonator unit. The simulation results show that, in the3dB, this filter’s cutoff frequency is more than4GHz, and the stop band is5-10GHz. compared to traditional stepped impedance micro-strip low-pass filter, its stop band has widened by30%, and the pass band is also broadening significantly.,Based on the traditional micro-strip band pass filter with ladder coupling, this design has changed the current path and reduced its discontinuity, so as to achieve the purpose of a better band performance and the better suppression of a second harmonic. Micro-strip fractal technology can reduce the filter pass band echo loss effectively and improve the filter’s stop band performance.On the other hand, the combination of the new materials and the new type micro-strip filter structure under the new process design, such as the current popular low temperature co-fired ceramic (LTCC), is also a research direction which is worth discussing. It is believable that this combination will improve the performance of micro-strip filter further.