A Feed circuit component definition is an active component that allows users to specify a voltage or current source. It consists of RLC components and an input waveform that modifies the electric field on its cell edge.
Double-clicking on a circuit component in the Definitions branch of the Project Tree opens the Circuit Component Definition Editor, where a feed is created by choosing Feed from the Type drop-down menu. The top group of controls define the layout of the RLC components with the source.
- Resistance: source resistor.
- Inductance: source inductor.
- Capacitance: source capacitor.
- RLC Arrangement: determines whether the RLC components are treated in parallel or in series. The series and parallel options affect only the configuration of the RLC elements and not their relation to the source. As such, the RLC components are always in series with a voltage source or in parallel with a current source.
- Matching Circuit: specifies which netlist component is used as the feed's matching network.
- Feed Type: chooses between a voltage and current source.
Specifying a two port matching circuit enables a Matching Circuit Arrangement option that allows users to decide whether the network is in series with or parallel to the source resistor. Additionally, the source inductor and capacitor must be zero when a matching network is specified.
The bottom group of controls defines the waveform and how it is applied to the simulation space.
- Amplitude: the peak, not RMS, value of the input waveform used to compute available power.
- Phase Shift: applied to the associated waveform, but only if the waveform is a sinusoid.
- Time Delay: applied to the associated waveform, but only if the waveform is not a sinusoid.
- Waveform: associated waveform definition applied to the source.
Users should note that either Phase Shift or Time Delay will be applied depending on whether or not the waveform is a sinusoid.
Pi Matching Network Example
Consider a Pi matching network for a simple antenna. Rather than creating three circuit components and laying them out in XF's geometry window, the matching network can be defined in the feed definition using a netlist component by following these steps:
- Determine the schematic layout and component values of the matching network.
- Define the matching network in XF as a netlist component.
- Select the netlist component in the feed definition editor.
- Place the matched feed on a single cell edge in the FDTD simulation space as a Circuit Component.
In this example, the matching network has three external ports that plug into the feed. When S-parameters are computed, S11 will be measured between the source resistor and port 1 of the matching network.