Z-Parameters of a Lattice Network
Lattice Network Setup
A lattice network typically has two diagonal impedances:
- Za (one diagonal)
- Zb (the other diagonal)
The Easy Trick
z11 = z22 = (Za + Zb) / 2
z12 = z21 = (Zb - Za) / 2
How to Remember It
- Sum → diagonal terms → divide by 2
- Difference → off-diagonal terms → divide by 2
Add → self impedance (z11, z22)
Subtract → mutual impedance (z12, z21)
z = (1/2) × [ (Za + Zb) (Zb - Za)
(Zb - Za) (Za + Zb) ]
(Zb - Za) (Za + Zb) ]
Symmetry shows:
- z11 = z22
- z12 = z21
When This Works
- Standard symmetric lattice network
- Only two diagonal impedances are present
Off-diagonal term = (Zb − Za)/2. Don’t mix the sign!
If you forget, derive once by open-circuiting a port—you’ll remember the pattern easily.