How it works
Z-parameters are found by open-circuiting one port and driving the other with a known current; Z11 = V1/I1 with I2 = 0. Y-parameters do the dual: short-circuit a port, drive with voltage, measure current. The h-parameters mix the two — h11 is input impedance with output shorted, h21 is forward current gain (hFE for a BJT, typically 100–300). ABCD parameters, used in transmission line cascades, let you multiply matrices for each section so a 50 Ω coaxial segment simply becomes one 2×2 matrix in a chain.
Key points to remember
Six sets of parameters exist, but examiners almost always focus on Z, Y, h, and ABCD. Conversion between parameter sets is tested heavily — know that [Y] = [Z]⁻¹. For a reciprocal network, Z12 = Z21 and Y12 = Y21; symmetry adds Z11 = Z22. The h-parameter set is the favourite for transistor models because h21 directly gives current gain. ABCD parameters satisfy AD − BC = 1 for any reciprocal two-port — that determinant condition appears in every Anna University model paper.
Exam tip
The examiner always asks you to find h-parameters from a given Z-parameter set, so memorise the conversion table: h11 = ΔZ/Z22, h12 = Z12/Z22, h21 = −Z21/Z22, h22 = 1/Z22.