Simulation can be expensive, especially when adding essential function modules to a suite of programs. But for those hoping to perform some basic linear circuit and system simulations, cost need not be an issue, especially when considering Ansoft Designer SV (Student Version) software from Ansoft Corp. (Pittsburgh, PA). The suite of linear-simulation tools provides a long list of capabilities, from a complete set of linear-component electrical models to filter synthesis and physics-based distributed models, all encompassed in a modern integrated design suite—and it's free.

Ansoft Designer SV features the same desktop design environment utilized by the company's commercially available high-frequency electronic-design software, Ansoft Designer and Version 9 of the electromagnetic (EM) simulator High-Frequency Structure Simulator (HFSS). The environment includes fully integrated schematic and layout editors, dynamic project and solution managers, advanced results graphing, post-processing, a three-dimensional (3D) viewer, and a scripted and parameterized footprint editor. The state-of-the-art solver technology includes a complete linear-circuit simulator, a complete set of physics-based linear distributed transmission-line models, discontinuities, commercial components, and ideal circuit elements. Circuit-simulation results includes S, Y, and Z parameters, VSWR, insertion and return loss, gain, stability circles, noise figure, and group delay.

The integrated schematic capture and layout editors in Ansoft Designer SV operate on a single database, which allows physical and symbol views of a design to be fully synchronized, and designers can work from either view. A change made to any component parameter is applied to the component and automatically updated in both views. This makes it possible to get a real-time understanding of a circuit's electrical performance and physical layout.

Ansoft Designer SV also provides a full set of transmission-line models and a utility to characterize them before placement into a circuit or system. Transmission lines and couplers can be analyzed and synthesized in seconds using the integrated transmission-line (TRL) utility. By entering the electrical properties, the tool will automatically synthesize the physical description or vice versa. The TRL utility includes microstrip, stripline, and coplanar waveguide mediums.

Like its commercially available version, Ansoft Designer SV offers a very large set of distributed models for common and obscure geometries required for RF and microwave circuit design. Mediums include microstrip, stripline, coplanar waveguide, grounded coplanar waveguide, and coaxial cables. The physics-based models perform over wider frequency ranges making them ideally suited for millimeter-wave applications. The software also uses Ansoft's approach to discontinuity modeling, which is derived from a solvable electromagnetic problem. In doing so, greater accuracy is assured.

The most accurate approach to characterizing full-wave, uniform, coupled transmission lines is by the spectral-domain method employed by Ansoft Designer SV. This method is fast and accurate and boasts a wider range of applications than other methods.