Free Software Computes Impedance Transitions

Feb. 18, 2011
This handy utility program can be used when matching the different impedances of transmission lines in standard circuit formats, including microstrip, stripline, and coplanar-waveguide circuits.

Matching impedances is essential to achieving reflection-free signal flow in passive high-frequency circuits and high efficiency in active circuits. although most engineers have preferred approaches to matching impedances to a system's characteristic impedancetypically 50 O in RF/microwave circuitsmaterials supplier Rogers Corporation offers a backup plan that doesn't cost a thing: the company's free mWi-2010 microwave impedance calculator software.

This handy program is available as a free download from the Rogers website. the software runs on most Windowsbased personal computers and provides fast and easy calculations of key transmission-line parameters. One catch: The software is based on the use of Rogers' high-frequency laminate materials. Fortunately, the company offers extensive lines of laminates with a wide range of dielectric properties to suit the needs of the most demanding RF/ microwave circuit designs through millimeter-wave frequencies. Rogers' circuitboard laminates are based on polytetraflurorothylene (PTFE), thermoset resins, and other dielectric materials typically reinforced with glass fibers, spheres, and other fillers for dimensional stability.

The microwave impedance calculator is a simple-to-use design utility program that uses proven closed-form equations to determine the impedance and loss of a wide range of different circuit types, including microstrip and stripline designs. it was written by John coonrod, market development engineer for Rogers' advanced circuit materials division, who has created a wide variety of high-frequency circuits based on his company's laminates and assistance from the mWi- 2010 software.

An operator can initiate an analysis for a particular circuit type and material by selecting a transmission-line technology, such as microstrip or stripline, and a material of choice from on-screen menus (see figure). the materials are listed along with relative dielectric constants, dissipation (loss) factors, thermal conductivity, and thermal coefficient of dielectric constant. moving a mouse cursor over any material brand name will reveal additional information about the material.

Operators can enter parameters specific to their circuit application, including target frequency and RF power level. Using the program, they can synthesize or analyze a number of transmissionline parameters, such as conductor width and conductor spacing for a target impedance, using models for a variety of transmission-line technologies, such as coplanar waveguide, stripline, and microstrip (including an improved edge-coupled microstrip model). the software can provide results as a table or file of information for a range of operating frequencies, showing data in english or metric equivalents. it can even calculate the temperature rise above ambient temperature for a selected laminate based on an input RF power level. the software is supported by a 22-page manual downloadable in PDF format.

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