T-Network Topology
Port 1 ── L₁ ── Node ── L₂ ── Port 2
│
C (shunt)
│
GND
T-network: series-shunt-series = L₁, C (shunt), L₂
Provides high-impedance virtual node → good for bandpass behavior
Q can be set independently of impedance ratio (like Pi)Design Equations
Given: Z_source = 50Ω, Z_load = 50Ω, design Q = 3 (bandpass)
(Note: T-network can match equal impedances with nonzero Q → bandpass filter behavior)
Virtual resistance R_v at node: R_v = Z_source × (1 + Q²) = 50 × 10 = 500Ω
Left side (Z_source to R_v):
X_series_L1 = Q × Z_source = 3 × 50 = 150Ω → L₁ = 150/(2π×900MHz) = 26.5nH
X_shunt = R_v / Q = 500/3 = 166.7Ω (half, shunted) → actual C depends on both sides
Shunt element C (at node):
X_C = Z_source × (1 + Q²) / Q = 50 × 10/3 = 166.7Ω → C = 1/(2π×900MHz×166.7) = 1.06pF
Right side (R_v to Z_load):
X_series_L2 = Q × Z_load = 150Ω (same as L₁ for equal impedances)
→ L₂ = 26.5 nHT-Network vs Pi-Network Choice
| Criteria | Choose T-Network | Choose Pi-Network |
|---|---|---|
| Source/load impedance | High source impedance | Low source impedance |
| Layout | Series elements easier to place | Shunt elements easier to ground |
| Harmonic suppression | Moderate | Better (shunt elements at both ends) |
RF View: Auto Match can synthesize T-networks as an option. Build manually in Circuit Simulator: Series L₁ → Shunt C → Series L₂. Verify S11 and BW. Free on Android.