Impedance and power-handling calculator for RF materials

July 30, 2014 // By Jean-Pierre Joosting
Isola is pleased to announce a free Impedance and Power-Handling Calculator that predicts the design attributes for microstrips and striplines based on the design’s target impedance and dielectric properties of the company’s RF, microwave and millimeter-wave laminate materials.

This tool supports Isola’s earlier announcement of a Design Review Service, in which its technical staff will provide PCB fabricators and OEMs all of the calculations, testing, characterizations and material recommendations needed to convert to Isola’s materials. This service is offered in the wake of the global shortage of competitive RF substrates.

The dielectric properties calculated by this tool include the effect of dielectric anisotropy, the difference when measured along different axes in a material's dielectric constant and dissipation factor. Almost all substrates have some degree of anisotropy, which is primarily driven by the reinforcements used such as fillers or woven fabrics. The difference in dielectric constant is not as significant for striplines, as the dielectric is homogenous and the propagation occurs in the transverse electromagnetic (TEM) mode with the magnetizing field (“H” plane) and the electric field ("E" plane) orthogonal to each other. However, the difference in dielectric constant is significant in microstrips where propagation occurs in a quasi-TEM mode and where there are components of the field in both perpendicular and parallel planes. The measured dielectric constant is therefore not accurate for modeling the microstrip, as most measurements are carried out in the Z-direction and the X and Y measurements are not readily available.

Isola’s software tool provides a design or an equivalent dielectric constant to facilitate modeling for PCB designers to predict impedance and other design attributes. The software computes changes in the effective dielectric constant due to dispersion at higher frequencies. The software then computes the total insertion loss – a measure of power lost through heat for power handling calculations, including the dielectric loss, conductor loss, and the loss due to the surface roughness. The main factors affecting the typical power-handling capability of a material are its thermal conductivity, the maximum operating temperature, and the total insertion loss.

The Impedance and Power-Handling Calculator is available for download at

A tutorial for the calculator