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Band pass (400 rad/s, 150 rad/s) from 1 dB ladder

Short answer

Using LP→BP transformation s→(s²+ω₀²)/(Bs) with ω₀=400 rad/s, B=150 rad/s: series 1.2817 H becomes 8.545 mH series 731.5 µF; shunt 1.9093 F becomes 12.73 mF ∥ 491.0 µH; series 1.4126 H becomes 9.417 mH series 663.7 µF; shunt 1.0495 F becomes 6.997 mF ∥ 893.3 µH; 1 Ω terminations.

Following circuit is a low pass filter having αp = 1dB and ωp = 1 rad/s. Obtain a bandpass filter ω0 = 400 rad/sec and bandwidth of 150 rad/sec. [Figure: source V1, 1 Ω source resistor, series 1.2817 H, shunt 1.9093 F, series 1.4126 H, shunt 1.0495 F, 1 Ω load]

Use the low-pass to band-pass transformation s→s2+ω02Bss \to \dfrac{s^2+\omega_0^2}{Bs} with ω0=400\omega_0 = 400 rad/s (ω02=1.6×105\omega_0^2 = 1.6\times10^5) and B=150B = 150 rad/s. The prototype has αp=1\alpha_p = 1 dB at ωp=1\omega_p = 1 rad/s, so the band-pass filter will have 1 dB ripple between band edges ω1,2=4002+752∓75=331.97\omega_{1,2} = \sqrt{400^2+75^2} \mp 75 = 331.97 and 481.97481.97 rad/s.

Element rules:

  • series LL → series L′=L/BL' = L/B and C′=B/(Lω02)C' = B/(L\omega_0^2);
  • shunt CC → parallel C′=C/BC' = C/B and L′=B/(Cω02)L' = B/(C\omega_0^2).

Given ladder: series 1.2817 H, shunt 1.9093 F, series 1.4126 H, shunt 1.0495 F, 1 Ω terminations.

1.2817 H:L′=1.2817150=8.5447 mH,C′=1501.2817×1.6×105=731.45 μF1.9093 F:C′=1.9093150=12.729 mF,L′=1501.9093×1.6×105=491.02 μH1.4126 H:L′=1.4126150=9.4173 mH,C′=1501.4126×1.6×105=663.67 μF1.0495 F:C′=1.0495150=6.9967 mF,L′=1501.0495×1.6×105=893.28 μH\begin{aligned} 1.2817\ \text{H}:&\quad L' = \frac{1.2817}{150} = 8.5447\ \text{mH},\quad C' = \frac{150}{1.2817\times1.6\times10^5} = 731.45\ \mu\text{F} \\ 1.9093\ \text{F}:&\quad C' = \frac{1.9093}{150} = 12.729\ \text{mF},\quad L' = \frac{150}{1.9093\times1.6\times10^5} = 491.02\ \mu\text{H} \\ 1.4126\ \text{H}:&\quad L' = \frac{1.4126}{150} = 9.4173\ \text{mH},\quad C' = \frac{150}{1.4126\times1.6\times10^5} = 663.67\ \mu\text{F} \\ 1.0495\ \text{F}:&\quad C' = \frac{1.0495}{150} = 6.9967\ \text{mF},\quad L' = \frac{150}{1.0495\times1.6\times10^5} = 893.28\ \mu\text{H} \end{aligned}
  Rs=1  [ Z1 ]        [ Z3 ]
 o-/\/\-[    ]--+-----[    ]--+------+---o
 |              |             |      |   +
 Vs          [ Y2 ]        [ Y4 ]  RL=1  Vo
 |              |             |      |   -
 o--------------+-------------+------+---o
ArmBand-pass element
Z1 (series)8.5447 mH in series with 731.45 μF
Y2 (shunt)12.729 mF ∥ 491.02 μH
Z3 (series)9.4173 mH in series with 663.67 μF
Y4 (shunt)6.9967 mF ∥ 893.28 μH

Each pair resonates at 400 rad/s (e.g. 1/8.5447 mH×731.45 μF=4001/\sqrt{8.5447\text{ mH}\times731.45\ \mu\text{F}} = 400). These values are for 1 Ω1\ \Omega terminations. For practical values, magnitude-scale by kmk_m (e.g. km=1000k_m = 1000 for 1 kΩ terminations): multiply every L by kmk_m and divide every C by kmk_m.

✓ Answer checked by Claude Sonnet 5.5

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