Calculadora de Atenuador RF
Atenuadores T, Pi e Bridged-T
Required Parameters
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Quick Answer
An RF attenuator reduces signal power by a precise dB amount while maintaining impedance matching. For a T-pad in 50 ohm: R_series = Z0 x (K-1)/(K+1), R_shunt = 2Z0K/(K^2-1), where K = 10^(dB/20).
Calculadora de Atenuador RF
Projete atenuadores resistivos T-pad, Pi-pad e Bridged-T para RF e audio.
Atenuador T-Pad
- R1 = Z0 x (K - 1) / (K + 1) onde K = 10^(A/20)
- R2 = 2 x Z0 x K / (K^2 - 1)
Ferramentas Relacionadas
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Design Notes
Resistive attenuators are frequency-independent in theory, but parasitic inductance and capacitance of physical resistors limit the usable frequency range. Through-hole pads work to about 100 MHz; SMD 0402 pads extend to 6 GHz. For broadband precision, use thin-film attenuator chips rated for your frequency range. Always verify return loss (>20 dB) and ensure each resistor can handle its share of the dissipated power.
Common Mistakes
- 1
Using a simple voltage divider instead of a matched-impedance pad — this causes reflections and VSWR problems.
- 2
Ignoring resistor power dissipation — at high attenuation, nearly all input power is dissipated as heat in the resistors.
- 3
Using wirewound resistors at RF frequencies — parasitic inductance destroys the flat frequency response above a few MHz.
Engineering Handbox
1. Calculate K = 10^(6/20) = 10^0.3 = 1.995\n2. R_series = 50 x (1.995-1)/(1.995+1) = 50 x 0.332 = 16.6 ohm\n3. R_shunt = 2 x 50 x 1.995 / (1.995^2 - 1) = 199.5 / 2.98 = 66.9 ohm
Knowledge Base
Para que serve um atenuador Pi?
Reduz a potência do sinal mantendo a impedância característica (50 ou 75Ω) para evitar reflexões.
Como escolher entre T e Pi?
T: menor capacitância parasita (melhor para RF). Pi: mais fácil em PCBs. Abaixo de 1 GHz, diferença mínima.
Fórmula do atenuador T?
R_série = Z0×(K-1)/(K+1), R_shunt = 2×Z0×K/(K²-1), onde K = 10^(dB/20).
Tolerância dos resistores?
Laboratório: 1% mínimo. Produção RF: 0,1% para atenuações acima de 20 dB.
Como cascatear atenuadores?
Some os valores em dB. 3 dB + 6 dB = 9 dB total.
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