Bridged-T Attenuator Calculator
Calculate resistor values for a matched Bridged-T network. Ideal for variable attenuators (only 2 resistors change).
Bridged-T Features
Engineering Principles: Bridged-T Attenuator Network
The Bridged-T attenuator is an improved variation of the T-pad attenuator. It modifies the T-pad by 'bridging' two series resistors with a single resistor. The main advantage is that characteristic impedance (Z0) can be maintained while varying attenuation by changing only two resistors.
Resistor bridging the input and output lines.
Shunt resistor to ground.
The two fixed series resistors are equal to Z0.
Technical Notes
- •Often used in variable attenuators because only two resistors (R1 and R2) need to change to adjust attenuation while Z0 stays constant.
- •The topology is self-matched to Z0 if R_fixed = Z0.
- •Provides excellent high-frequency performance.
Frequently Asked Questions
Why use a Bridged-T instead of a Pi or T pad?
The Bridged-T attenuator allows you to vary the attenuation while keeping the characteristic impedance constant by changing only two resistors (R1 and R2). In contrast, Pi and T pads typically require adjusting three components simultaneously to maintain a perfect match.
What is the insertion loss of a Bridged-T network?
The insertion loss is determined by the specific resistance values chosen. The network is designed to provide a specific attenuation (e.g., 3dB, 6dB, 10dB) when inserted into a transmission line of the correct impedance Z0.
Can I use standard resistor values?
Likely not. Calculated resistor values are often precise decimals (e.g., 52.3Ω). You will need to use E96 (1%) or E24 (5%) series resistors that are closest to these values, which may introduce a slight impedance mismatch or attenuation error.