Ultra-wideband Microstrip High-pass Filter

Since the ultra-wideband(UWB) was officially approved for commercial purposes, the RF devices which can be applied this band develop rapidly. Microwave highpass filter is a device that allows the part of signal frequencies higher than cut-off frequency to pass without attenuation and inhibits the frequencies lower than cut-off frequency. Highpass filter is generally formed by semi-lumped elements[1] or distributed elements[2,3] perioadically loaded, but due to the frequency response of a periodic periodic structure, in practice, it does not exist the ideal highpass frequency response, so actually we usually refer to highpass filter is a pseudo-highpass filter.Although so far there have been many domestic and foreign experts on highpass filter research and design, there are still some problems, such as bandwidth is not wide enough, band rejection is not good enough, and so on. Thus, the primary purpose of this paper is to design a microwave filter bandwidth is wide enough, while other indicators are also excellent. The main work is as follows:1. Using the defect ground structure(DGS structure), short-circuit and open-circuit stubs to design highpass filter. DGS structure can change the values of the equivalent inductance and capacitance by changing the effective permittivity of the transmission line. In addition, if the physical sizes of two transmission lines are equal, the DGS structure’s electrical length will be more longer than conventional transmission line. Therefore, in the case of the same electrical length, the physical length of the DGS structure would naturally shorter so that to achieve the miniaturization demand. While the design takes advantage of open-circuit stub to produce transmission zero. Final test gets 133% of fractional bandwidth and a certain rejection out of the passband.2. Making use of the traits of low insertion loss and wide band of suspended stripline to design of the highpass filter. It will create series resonant circuit, resulting in transmission zeros out of the band, by T inductance and the coupling capacitance between metal patch. So the filter has a good band rejection and final test gets 133% of fractional bandwidth and 40 dB rejection at 4.2 GHz.