Equations

As mentioned earlier, a variable may be defined by a constant, another variable or an equation. An equation is composed of constants and/or variables. Below are some examples of valid equations.

•    3*3
•    3*pi
•    3*H
•    sin(H)
•    sqrt(H)

The last three equations are ones in which one variable is used to define another. This allows you to relate properties in your circuit such that changing one effects the other, maintaining a set relationship between them. For example, you wish to define a dielectric layer which is always five times the thickness of your substrate. To do so, you define a variable “sub” which you would enter as the thickness of your substrate. Then you would enter “5*sub” as the value for the thickness of the dielectric layer. There are two methods you may use to do this. The first is to define another variable “die_thick” which you define as “5*sub” and the second is to simply enter the equation “5*sub” as the thickness of the dielectric layer. You may enter an equation in any field in which you may enter a variable.

Available functions for equations include:

•    Operators such as addition, subtraction, multiplication, etc.
•    Logarithmic functions
•    Complex Math functions
•    Trigonometric functions
•    General Mathematical functions such as maximum or minimum
•    Conversion functions for converting units
•    Table function to use for data lookup

There are also constants available for equations including project constants such as the cell size and box size and the frequency which are discussed more below.

For complete details on all the functions and constants available for equations and their syntax, please refer to Equation Syntax

If you enter an equation which uses a variable as the definition of another variable, then the variable defined by the equation is dependent on the variable used in the equation. This is discussed later in Dependent Variables.

Frequency Dependency

There is a frequency constant, FREQ, available for use in Sonnet equations. This allows you to model properties whose characteristics are frequency dependent such as a dielectric. It is important to be aware that if a variable uses the FREQ constant in its definition that the value of the variable changes during the analysis even if the variable is NOT selected for the parameter sweep or optimization.