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Frequency and magnitude scaling to 10⁵ rad/s

Short answer

Set kf=1e5 for ωo=1e5 rad/s. Choose km=1000 for 1 kΩ terminations. Scaled: R1=R2=1 kΩ, L1=L2= (1000×2.024)/1e5 = 20.24 mH, C1=0.994/(1000×1e5)=9.94 nF (≈10 nF). Cutoff at 1e5 rad/s (≈15.9 kHz).

Define normalization and denormalisation. Following circuit is a lowpass filter designed at normalization frequency of ωo = 1 rad/s. Apply frequency and magnitude scaling so that ωo = 10⁵ rad/s and practically realizable elements. [Figure 1: source V1, R1 = 1 Ω, series L1 = 2.024 H, shunt C1 = 0.994 F, series L2 = 2.024 H, load R2 = 1 Ω]

Normalization and denormalization

Normalization is designing the filter for ωo\omega_o = 1 rad/s and 1 Ω terminations, so that standard tables and simple numbers can be used. Denormalization is converting the normalized values to the actual frequency and impedance level using frequency scaling (kfk_f) and magnitude scaling (kmk_m):

R′=kmR,L′=kmLkf,C′=CkmkfR' = k_m R, \qquad L' = \frac{k_m L}{k_f}, \qquad C' = \frac{C}{k_m k_f}

Numerical

Given: R1=R2=1 ΩR_1 = R_2 = 1\ \Omega, L1=L2=2.024L_1 = L_2 = 2.024 H, C1=0.994C_1 = 0.994 F at ωo\omega_o = 1 rad/s. Required ωo=105\omega_o = 10^5 rad/s.

Frequency scaling factor: kf=105/1=105k_f = 10^5/1 = 10^5.

Magnitude scaling factor: with km=1k_m = 1 the capacitor would be 0.994/105≈10 μ0.994/10^5 \approx 10\ \muF and the resistors 1 Ω, which are not practical. Choose km=1000k_m = 1000 (1 kΩ terminations).

R1′=R2′=kmR=1000×1=1 kΩL1′=L2′=kmLkf=1000×2.024105=20.24 mHC1′=Ckmkf=0.9941000×105=9.94 nF\begin{aligned} R_1' = R_2' &= k_m R = 1000 \times 1 = 1\ \text{k}\Omega \\ L_1' = L_2' &= \frac{k_m L}{k_f} = \frac{1000 \times 2.024}{10^5} = 20.24\ \text{mH} \\ C_1' &= \frac{C}{k_m k_f} = \frac{0.994}{1000 \times 10^5} = 9.94\ \text{nF} \end{aligned}
 1k     20.24 mH      20.24 mH
 o-/\/\--UUUU----+----UUUU----+
 V1              |            |
              9.94 nF        1k   V2
                 |            |
 o---------------+------------+

Answer: R1=R2R_1 = R_2 = 1 kΩ, L1=L2L_1 = L_2 = 20.24 mH, C1C_1 = 9.94 nF (≈ 10 nF standard), with ωo=105\omega_o = 10^5 rad/s (≈ 15.9 kHz).

Check: L′C′L'C' product scales by 1/kf21/k_f^2: 2.024×0.994×10−10=20.24×10−3×9.94×10−92.024\times0.994\times10^{-10} = 20.24\times10^{-3}\times9.94\times10^{-9}, so the response shape is unchanged and only moved to 10510^5 rad/s. Any other kmk_m (e.g. 10 kΩ) is also correct if it gives practical values.

✓ Answer checked by Claude Sonnet 5.5

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