A Cavity Band-Stop Filter With Far Spurious Stop Bands

With the development of communication technology, electromagnetic environment surrounding communications equipment has become increasingly complex. The spectrum is divided into different frequency bands in accordance with the different application. To make the system work in each respective band, we need to use different types of filters to avoid the interference from external spurious signals and the interference from internal strong noise signal.Band-stop filter has a good inhibitory effect on the strong interference signals from one band or more points. And it can suppress the transmission of parts of the frequency signal and add the desired signal in a continuous spectrum. With these special features, band-stop filter is widely used in wireless communications, radar systems and other equipment. The band-stop filter has more than one stop-band as there are multiple modes in microwave cavity, which will affect the system work. So, we need to consider harmonic suppression in the filter design process to make the spurious stop band away from working frequency.This paper studies the cavity band-stop filter design methods of the further spurious stop bands, the wider band and the smaller size. The main work is as follows.1. The working theory and design methods of band stop filter are systematically researched.2. A metal post is added in rectangular resonant cavity as the loaded capacitance, and research the impact of loaded capacitance on the size of the resonator, quality factor and high-order mode position. Finally, we get the conclusion that load capacitance can suppress the spurious pass band far from the center frequency.3. The influence of different coupling ways on the filter bandwidth and the spurious stop bands are analyzed, and the transmission line is embedded in the slot of the load capacitance. The new method of coupling can also put the spurious stop band away from the main mode.4. Based on these theories, we can establish a separate cavity. Through simulating and optimizing, it works at 4.02 GHz, and the spurious stop band is far away from 20 GHz, and the quality factor of resonator is 1600. And the reflection coefficient in the working frequency band is less than-10 dB by tuning screws. Then, connect multiple of the same cavity to form a new band stop filter, whose frequency center at 4GHz. When the depth of restrain is less than-40 dB, its bandwidth reach 300 MHz. And its spurious stop band frequency is 5 times away from the center frequency. And it has the advantage of processing and tuning easily, high power capacity and lower insertion loss.