RF Journey.
Start learning
Menu
Tool 13 · Available

Attenuator Designer

Design equal-impedance T or π pads and evaluate rounded resistor values and dissipation.

Typical inputs
Equal reference impedance, attenuation, T/π topology, input power, and exact/E12/E24 selection.
Calculated output
Resistor values, realized attenuation, port matches, return loss, and resistor dissipation.
Model status
Release D · documented and numerically tested
Engineering question

Which resistor network gives the requested matched attenuation?

Matched resistive pad synthesis

Symmetric equal-impedance T and π pads are synthesized, then the chosen preferred values and tolerance corners are independently re-evaluated.

Topology
T pad selected values16.6139 Ω series each · 66.931 Ω shuntExact ideal resistances
series
16.6139 Ω—shunt to ground
66.931 Ω—series
16.6139 Ω
Exact series class
16.6139 Ω
Exact shunt class
66.931 Ω
Realized attenuation
6.000000 dB
Input impedance
50.000000 Ω
Input return loss
322.9682 dB
Output return loss
322.9682 dB
equal by reciprocal symmetric topology
Worst corner, ±1.00%
48.4896 dB RL
Corner attenuation range
5.9425…6.0580 dB
Output power
14.0000 dBm
Resistor 1 dissipation
33.2279 mW
Resistor 2 dissipation
33.3068 mW
Resistor 3 dissipation
8.34647 mW

Calculation path

  1. K=10A/20=1.99526231K=10^{A/20}=1.99526231
  2. Rs=Z0(K−1)K+1Rp=2Z0KK2−1\begin{aligned}R_s&=\frac{Z_0(K-1)}{K+1}\\R_p&=\frac{2Z_0K}{K^2-1}\end{aligned}
  3. ABCD evaluation verifies selected-value match and attenuation; four class-tolerance corners provide a bounded screen.
  4. Apply voltage, pulse, temperature, and power derating. Real RF behavior also depends on resistor technology, layout, and parasitic reactance.
Model

What this calculator is doing

Closed-form pad values are calculated first. Selected rounded values are then re-evaluated as a two-port so displayed loss and match describe the chosen parts.

Decision

How to read the result

Rate each resistor from its own dissipation with temperature and pulse derating. At RF, verify layout and parasitics as well as resistance.

Equations & conventions

  • K=10A20K = 10^{\frac{A}{20}}
  • T:Rs=Z0(K−1)K+1T: R_{\mathrm{s}} = \frac{Z_{0}(K-1)}{K+1}
  • A is positive matched attenuation in dB and K = 10^(A/20).
  • Z0 is equal real source/load reference impedance.
  • Dissipation assumes entered available source level and matched load.

Independently checked example

Checked example: a 6 dB, 50 Ω T pad uses about 16.614 Ω for each series arm and 66.931 Ω shunt; the exact network re-evaluates to 6 dB.

Common mistakes

  • Rounding values without recalculating match and loss.
  • Assigning total pad dissipation to every resistor.

Assumptions, validity & omissions

  • Source and load reference impedances are equal and real.
  • Resistors are ideal at the design frequency.
  • Power ratings need engineering derating and temperature review.

Sources & model provenance

← Back to all RF tools