Microstrip Lowpass Filter With Far Parasitic Passband

Microwave filters play an significant role in lots of microwave applications. They are used to separate or combine frequencies. The electromagnetic spectrum is limited and has to be shared. Filters are two-port networks which are used to select or confine the microwave signals from shared spectrum. Low-pass, high-pass, band-pass and band-stop filters can be achieved by setting different frequency response. Microwave filters have been widely used in microwave communications, radar test and measurement systems.With the rapid development of wireless communication system, some emerging applications continue to challenge microwave filters with ever more stringent requirements,such as higher performance, smaller size, lighter weight and lower cost. Miniature low-pass filters with high performance are in great demand for communication systems to suppress harmonics and spurious signals. Filters fabricated by printed circuit board(PCB) technology are generally preferable for their easy fabrication and low cost as well as easy integration with other microwave circuits. So how to design a miniature microstrip low-pass filter with far parasitic pass-band is what the thesis focus on.The theory and some general structures of designing microstrip low-pass filter with far parasitic pass-band have been summarized in this thesis. The structures may include open-stubs, stepped-impedance, resonators-coupling and DGS structures. The mainly work of the thesis includes:Firstly, the basic theory of designing microwave filters has been introduced. Which mainly includes Richards transform and Kuroda rules.Secondly, the common structures of designing microstrip low-pass filter with far parasitic pass-band have been introduced and simulated in electromagnetic simulation software CST. The advantages and disadvantages have been compared. What’s more, the innovation of structures have been presented and the theory has been studied.Finally,microstrip low-pass filters of elliptic type with sharp roll-off and far parasitic pass-band have been studied and designed. Microstrip stubs act as compact resonant cells which coupled with each other to achieve sharp roll-off characteristics. Besides, DGS structures have been introduced to broaden the stop-band.