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Design and analysis on micro-strip wide stop-band lowpass filters

Naiqiang Fan, Yingmin, Wang

Microwave filter is an important gadget in the microwave circuit; it can exert great impact on the whole microwave circuit. Now that people call more for the band allocation of electromagnetic wave, band resources become more finely allocated; the use of handheld mobile devices also have a higher expectation—high performance, low cost, miniaturization—for microwave devices, thus the micro-strip filter, a kind of microwave filter, comes into being with its high performance, low cost, small size and easy processing. Microwave low-pass filter are normally used in the front of the system to block the high frequency signals and protect circuit in the back; high attenuation over a wide stop-band frequencies is not only a hotspot of current research on microwave lowpass filter but also the attention of people. This paper analyzes the application of microstrip low-pass filter and is to design a low-pass filter with a wide stop-band and a fast decay speed. The paper is to design elliptic function low-pass filter with serial structure and parallel structure respectively; the design with and parallel structure is to be converted into micro-strip filters by employing the high-low impedance equivalent method and increasing the range of stop-band; the design with and parallel structure is made with hairpin cascade structure. Through the simulation calculation in HFSS, the paper is to design a 4 GHZ low-pass micro-strip filter with the reflection coefficients S11 being smaller than -12 db while the S21, smaller than -30 db.