- 2072 Magh · 5 marks
Immittance chart sketch and scales
Short answer
An immittance chart overlays impedance and admittance Smith charts on one Γ-plane. Impedance scale (red) reads r and x: constant-r circles touch open circuit (right), upper half +jx inductive. Admittance scale (blue) reads g and b: constant-g circles touch short circuit (left), upper half –jb inductive.
Sketch an immittance chart and compare the scales.
An immittance (ZY) chart overlays the impedance Smith chart and the admittance Smith chart (the Z-chart rotated by 180°) on one Γ-plane. It is usually printed in two colours.
+jx / −jb (inductive)
.-~~~~~~~~~~~~-.
/ Z: r-circles \
SC ( g-circles 1 → ) OC
z=0 \ ←touch SC / z=∞
y=∞ '-~~~~~~~~~~~~-' y=0
−jx / +jb (capacitive)
Comparison of scales
| Feature | Z (impedance) scale | Y (admittance) scale |
|---|---|---|
| Quantity read | r, x of z = r + jx | g, b of y = g + jb |
| Real-part circles | Constant r, touch at OC (right) | Constant g, touch at SC (left) |
| Imaginary arcs | Constant x, from the right end | Constant b, from the left end |
| Upper half | +jx (inductive) | −jb (inductive) |
| Lower half | −jx (capacitive) | +jb (capacitive) |
| Left end point | z = 0 (short) | y = ∞ (short) |
| Right end point | z = ∞ (open) | y = 0 (open) |
| Series L or C moves along | constant-r circle | — |
| Shunt L or C moves along | — | constant-g circle |
| Usual colour | Red | Blue/green |
The outer wavelength scales (WTG/WTL) and the radial scales (|Γ|, VSWR, return loss) are common to both.
✓ Answer checked by Claude Opus 5.5 (high effort)
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