Calculator Inputs
Tip: Use LC mode for tuned RF networks. Use RC or RL for quick first-order estimates and interface shaping.
Example Data Table
| Case | Type | f0 / fc (MHz) | BW (MHz) | Impedance (Ohms) | Order | Known Part |
|---|---|---|---|---|---|---|
| ISM Receiver Front End | Band-pass | 433.92 | 20 | 50 | 3 | 100 nH |
| RF Harmonic Cleanup | Low-pass | 100 | - | 50 | 5 | None |
| Interference Rejection | Band-stop | 1575.42 | 8 | 75 | 2 | 3.3 pF |
Formula Used
Angular frequency: ω = 2πf
Resonance: f0 = 1 / (2π√LC)
Companion capacitor: C = 1 / (ω0²L)
Companion inductor: L = 1 / (ω0²C)
Loaded Q: Q = f0 / BW
Series resonator estimates: L = QR / ω0, C = 1 / (ω0RQ)
RC cutoff: fc = 1 / (2πRC)
RL cutoff: fc = R / (2πL)
Butterworth attenuation slope: 20n dB/decade
For passband magnitude, the tool uses normalized transfer approximations. Butterworth response uses a maximally flat magnitude curve. Chebyshev Type I uses ripple factor ε = √(10^(Rp/10) - 1). Bessel mode keeps the same magnitude estimate for quick sizing, while prioritizing time-domain smoothness in practice.
How to Use This Calculator
- Select the filter type that matches your RF task.
- Choose the response family based on flatness, ripple, or transient goals.
- Enter impedance, order, and key frequency targets.
- For band-pass or notch work, provide center frequency and bandwidth.
- If you already own a coil or capacitor value, select the known component mode.
- Click the calculate button to show the result above the form.
- Review resonance, Q, reactance, slope, and amplitude estimate outputs.
- Export the current results as CSV or PDF for documentation.
Frequently Asked Questions
1. What does this calculator design?
It estimates core RF filter parameters for low-pass, high-pass, band-pass, and notch networks. It focuses on resonance, cutoff targets, Q, reactance, and simple section sizing for practical early-stage engineering work.
2. Is this suitable for final production layouts?
It is best for pre-design, hand checks, and quick comparisons. Final production filters should still be validated in a circuit simulator and confirmed against parasitics, tolerances, PCB effects, and measured S-parameters.
3. When should I choose Butterworth?
Choose Butterworth when you want a smooth passband and simple attenuation planning. It is a solid default for many RF cleanup tasks where flatness matters more than the sharpest transition band.
4. When should I choose Chebyshev?
Choose Chebyshev Type I when stronger roll-off is more important than perfectly flat passband gain. The ripple setting lets you explore the tradeoff between transition sharpness and passband variation.
5. Why does impedance matter so much?
Impedance changes required reactance levels and loaded Q. A 50-Ohm system and a 75-Ohm system will not use identical section values, even when center frequency and bandwidth remain unchanged.
6. What is loaded Q in this tool?
Loaded Q is the ratio of center frequency to bandwidth. Higher Q means a narrower, more selective filter section. Very high Q values may become harder to realize with practical component losses.
7. Can I use known capacitor or inductor values?
Yes. Enter a known coil or capacitor and the calculator solves the companion resonant part at the chosen center frequency. This is useful when inventory or preferred packages limit component choices.
8. Does the PDF export need extra libraries?
No extra package is required in the browser. The file uses the built-in print dialog for a clean PDF workflow, while CSV export creates a spreadsheet-friendly summary of the latest calculation.