DSMatch (Double-Stub Match)

Symbol

Parameters

Name	Description	Unit	Default
Subst	Microstrip substrate name	None	MSub1
F	Center frequency	GHz	1
Zin	Desired complex input impedance	Ohm	50
Zload	Complex load impedance to match	Ohm	100
Zstub1	Characteristic impedance of stub line 1 (nearest input)	Ohm	50
Zstub2	Characteristic impedance of stub line 2 (nearest output)	Ohm	50
Zline	Characteristic impedance of line between stubs	Ohm	50
Zfeed1	Characteristic impedance of line connected to port 1	Ohm	50
Zfeed2	Characteristic impedance of line connected to port 2	Ohm	50
Stub1Type	Stub 1 type (open or short circuit)	None	Open Circuit
Stub2Type	Stub 2 type (open or short circuit)	None	Open Circuit
Delta	Length added to stubs for tuning performance	mil	0

Notes

1. A double-stub matching network matches a complex load impedance (Zload) to a desired complex input impedance (Zin) using two shunt stubs and a connecting line.
2. An impedance match can be realized using any combination of stub types, although some combinations can be more realizable.
3. Zfeed1 and Zfeed2 are used simply to ensure that the input and output legs of the microstrip tee components are of the proper width.
4. The length of the line between the stubs is nominally chosen to be an eighth of a line wavelength. However, if this will not realize the match, the length of line is computed such that the rotated circle on the Smith chart encloses the load admittance.
5. MTEE component width constraint violations will be avoided generally by choosing similar characteristic impedances for the line, stub, and feed.
6. Since two solutions are possible, the solution that results in the smallest length of stub 1 is chosen. For example, if stub 1 is open circuited, the solution for which stub 1 must realize a capacitive reactance is chosen.
7. The input port termination is set to the conjugate of Zin so that the ideal input reflection coefficient will be zero. The output port termination is set to Zload.
8. The optimization minimizes the value of S11 (referenced to the conjugate of Zin) at the design center frequency by changing the length of the stubs. Both stubs are tuned by the same length.
9. A SmartComponent subnetwork is empty until the Design Assistant is used to generate the design. Refer to Design Assistant.

For a more detailed discussion of this device, see: D. M. Pozar, Microwave Engineering, 2nd Edition, John Wiley & Sons: New York, 1998, pp. 266-271.

Example

A double-stub matching network was designed to match a load impedance of 100 - j30 Ohms to a 50 Ohm line at a center frequency of 5 GHz with open circuited stubs. Tuning using the Optimization Assistant yielded a value of Delta =-31.633 mil.