MICapSG (Microstrip 1-port Interdigital Capacitor)

Symbol

Parameters

Name	Description	Unit	Default
Subst	Microstrip substrate name	None	MSub1
F	Center frequency	GHz	1
C	Capacitance	pF	1
W	Width of fingers	mil	5
G	Gap between fingers	mil	5
Ge	Gap at end of fingers	mil	5
Np	Number of finger pairs	None	3
Wt	Width of interconnect	mil	25
Wf	Width of feed line (0 if Zf specified)	mil	0
Zf	Characteristic impedance of feed line; 0 if Wf specified	Ohm	50
Delta	Length added to fingers for tuning performance	mil	0

Notes

1. MICapSG designs a series capacitance between a microstrip line and ground using interdigital fingers. The underlying design uses the MICAP3 component contained in the Tlines-Microstrip palette.
2. The design is accomplished using a simple model that specifies the length required to achieve the capacitance C at the design center frequency given the remaining physical parameters. If the computed length is unreasonable, decreasing or increasing the gap G will increase or decrease the capacitance, respectively and therefore allow altering of the length.
3. Both Wf and Zf specify the properties of the feed line. For proper operation, make sure that only one of these parameters is non-zero.
4. For more detailed discussion of the parameters W, G, Ge, Np, Wt, and Wf, please refer to the discussion of MICAP3 in the Microstrip Components documentation.
5. The Optimization Assistant tunes the length of the fingers to achieve the desired capacitance. Because of the simple design approach used, it is often wise to first roughly tune the design within the Simulation Assistant and subsequently use the optimizer to perform the fine tuning.
6. A SmartComponent subnetwork is empty until the Design Assistant is used to generate the design. Refer to Design Assistant.

Example

A MICapSG component was used to design a 1 pF capacitance for a 50 Ohm line at a center frequency of 5 GHz. Optimization yielded a value of Delta = -1.841 mil.