Design And Research Of Wide Stopband Microstrip Low-Pass Filter

Microwave filter is one of the most important devices in microwave circuit, whose filtering characteristics directly affect the operation of the entire microwave circuit system. And now, the bandwidth of microwave resources are divided more and more fine. The wide application of handheld mobile devices also requires high performance, miniaturization, low cost microwave device. And microstrip filter becomes one of the main forms of microwave filter because of its high-performance, easy-to-manufacture, small size and low cost.Microwave low-pass filter is usually used in the front of the circuit system, used to isolate the high frequency signal and protect the circuit back of it. People always wish it has a steep attenuation and enough wide stopband scope, therefore, high performance, wide stopband is becoming a hot spot of current research on microwave low-pass filte.In this thesis, the mainly effort is the design theory and technology of the high performance wide stopband microstrip low-pass filter, including stepped-impedance resonator filter(SIR), DGS structure low pass filter and hairpin filter. The mainly work of this thesis includes:First of all, the technologies about microstrip filter have been summarized, which is based on consult a vast amount of domestic and international literature. Then a detail study on the technological achievements of broadening the stopband has been carried out.Secondly, the basic theory of designing a microstrip filter has been introduced, including the detailed process how to convert the normal lumped low-pass filter to microstrip filter using Richards transform, Kuroda rules and stepped-impedance resonator equivalent method.Thirdly, the design results of microstrip low-pass filter used DGS structure has been introduced. Then a detail study on the classic dumbbell DGS structure, which equivalent circuit is extracted, is carried out. And a serpentine aperture DGS structure is put forward, which increases the equivalent capacitance of the circuit and results in lower attenuation frequency and more steep slope of the stopband characteristics. Fourthly, the method of design a wide stopband low-pass filter, using stepped-impedance resonator equivalent, has been detailed studied, and a stepped-impedance low pass filter with wide stopband has been simulated in the ADS and the HFSS.Finally, a elliptic low-pass filter with rapid decay and wide stopband characteristics has been achieved. On one hand, the tandem structure is transformed into microstrip filter using stepped-impedance resonator equivalent, and adds the interdigital structure to expand its stopband; On the other hand, parallel structure is directly equivalent to the hairpin resonator structure. Then a low pass filter is designed by the way of cascading the hairpin structure. Finally a modification with S-shaped slit hairpin structure was proposed which has a lower resonant frequency and steeper attenuation edge.