Microstrip circuit design using PUFF

This paper proposes the use of PUFF to simulate microstrip circuits. This material is suitable for an undergraduate technical elective course in microwave integrated circuit design or an advanced course in analog communication systems design. Presently, many software packages, such as TOUCHSTONE from EESOF, are available to simulate microstrip circuits. These programs have several disadvantages. First, the cost is very expensive for usage in an educational environment. Second, the source code is unavailable, preventing modification for particular applications. For the above reasons, PUFF is used to simulate microstrip circuits. In this paper, PUFF will be used for the analysis and design of a microstrip bandstop filter. The design procedure consists of first designing the lumped-element lowpass filter prototype. This includes determining the filter order for the given filter specifications, determining the elemental values based upon the filter order, and scaling the elemental values for the appropriate frequency and system impedance. Transmission line filter design is an extension of this procedure by re-normalizing the elemental values to obtain the transmission line impedances. The resulting filter can be manufactured using coaxial transmission lines, but microstrip filters, which are planar structures, require the removal of all series stubs. For the design of microstrip filters, Kuroda's identities are used to remove the series stubs, and the elemental values are renormalized to obtain the transmission line impedances.