RF Attenuator Designer
Calculate resistor values for Pi, T, L, and Bridged-T attenuator pads. Pi and T pads work with equal impedances and provide precise attenuation. L-pads match two different impedances while attenuating. Bridged-T gives constant input/output impedance with minimum component count for high attenuation.
Equations & Parameters ▸
Pi: \(R_1=R_3=Z_0\!\dfrac{K+1}{K-1},\quad R_2=Z_0\dfrac{K^2-1}{2K}\quad K=10^{A/20}\)
| A | Attenuation in dB. Positive value = signal reduction. |
| Z₀ | Characteristic impedance (equal on both ports for Pi/T). Typically 50 Ω. |
| Z_S/Z_L | Source and load impedances for L-pad (can differ). |
| Pi | Two shunt resistors + one series resistor. Good for PCB layout. |
| T | Two series resistors + one shunt resistor. Symmetric, good for cable use. |
| L-pad | One series + one shunt resistor. Matches AND attenuates two different impedances. |
| Bridged-T | Efficient for large attenuation values. |
Physical constants used
| c | Speed of light = 2.998×10⁸ m/s |
| µ₀ | Permeability of free space = 4π×10⁻⁷ H/m ≈ 1.2566×10⁻⁶ H/m |
| ε₀ | Permittivity of free space = 8.854×10⁻¹² F/m |
Inputs
dB
positive valueTypical: 50 Ω or 75 Ω
Results
Component Values
R₁—
R₂—
R₃—
Exact attenuation—
Min return loss—
Diagram