# Defining the Environment

## Ground Plane Options

Go to the Setup tab in the main window and select the **Environment** panel. The relative permittivity and permeability of the surrounding medium can be set in the Medium box, Fig. 1.

Four options are available for the ground plane:

###### None

None ground plane is used. The simulation will be performed in **free space** with the permittivity and permeability set in the Medium box, Fig. 1.

###### Perfect

An infinite perfectly electric conducting (PEC) ground plane will be placed at the specified height from the xy-plane, Fig. 2. Thus, the ground plane will be parallel to the xy-plane. The Z value defines the ground plane height above the xy-plane. A negative Z defines the ground plane below the xy-plane.

###### Real

A real ground plane having the conductivity and the relative permittivity (relative permeability is 1) set by the user will be placed on the xy-plane (z = 0), Fig 3. There are three options for the real ground calculations: *Sommerfeld-Wait/Asymptotic*, *Reflection Coefficients/Asymptotic*, and *Radial wire ground screen*.

###### Substrate

A dielectric substrate having the permittivity set by the user will be placed below the xy-plane (z = 0), Fig. 4. The substrate can either be infinite or finite in the xy-plane. The slab thickness, h, along the z-axis must be specified. A perfectly electric conducting (PEC) ground plane will be placed at z = -h (just below the dielectric slab), Fig. 5.

### Real Ground Options

###### Sommerfeld-Wait/Asymptotic

The currents flowing on the antenna/wire structure are computed using a model that consists of a PEC ground plane and the addition of equivalent loss impedances that account for the power dissipated in the ground plane when there are connections to ground. This is a very good model, developed by Prof. James R. Wait, to obtain the input impedance of low (LF) and medium frequency (MF) antennas, where the ground conductivity is high at those bands. The ground finite conductivity and permittivity are also used to compute the near- and far-fields radiated from the structure using the Sommerfeld-Norton asymptotic expressions and the Fresnel’s reflection coefficients, respectively.

Connections to ground are allowed (start or end point of a wire having z = 0) and will be considered imperfect by default (currents flowing between ground and the grounded wires produce power losses in the ground). If the option “**Zero-Ohm connections to ground**” is checked, the wire connections to ground will be considered perfect (no ground power dissipation about the connection point).

###### Reflection Coefficients/Asymptotic

The ground parameters will affect the current distribution on the antenna or wire structure above ground via a generalization of the Fresnel’s reflection coefficients, so the input impedance of a transmitting antenna will also be affected by the real ground. The near and far fields will also be affected by the finite ground conductivity and its dielectric constant. Near fields are computed using the Sommerfeld-Norton asymptotic expressions, so the electric/magnetic field can be calculated as a function of distance from a transmitting antenna to observe the attenuation due to ground losses. The far-field is computed using the standard Fresnel’s reflection coefficients.

Wire connections to ground are allowed, but they will be considered as lossless connections.

###### Radial wire ground screen

A ground screen composed of buried radial wires will be placed below the ground plane. The screen is centered at the origin of coordinates and has the number of radial wires, wire length (or radius of the circular screen) and wire radius specified by the user. The ground screen model affects the current distribution on the antenna/wire structure by computing the power dissipated in the ground plane-wire screen system, so the input impedance of a transmitting antenna above the ground screen will be influenced by the presence of the screen and the finite ground conductivity. The ground finite conductivity and permittivity are also used to compute the near- and far-fields radiated from the structure using the Sommerfeld-Norton expressions and the Fresnel’s reflection coefficients, respectively.

Connections to ground are allowed (start or end point of a wire having z = 0) and will be considered imperfect by default (currents flowing between ground and the grounded wires produce power losses in the ground). If the option “**Zero-Ohm connections to ground**” is checked, the wire connections to ground will be considered perfect (no ground power dissipation about the connection point).