Example Data Table
| Use Case |
Filter Type |
Passband MHz |
Stop MHz |
Substrate |
Target Ohms |
Expected Output |
| WiFi front end |
Band Pass |
2400 to 2500 |
2200 |
3.48 |
50 |
Width, order, resonator length, and loss |
| Receiver preselector |
Low Pass |
0 to 900 |
1300 |
4.2 |
50 |
Cutoff layout length and selectivity order |
| High frequency cleanup |
High Pass |
1800 to 1800 |
1200 |
2.94 |
50 |
Line geometry and estimated unloaded Q |
Formula Used
Stripline impedance: Z0 is estimated as 30π divided by the square root of Er and the sum of W/B plus 0.441. This gives W/B for an initial centered stripline layout.
Guided wavelength: guided wavelength equals free space wavelength divided by the square root of relative permittivity.
Quarter wave length: length equals guided wavelength divided by four. Half wave length equals guided wavelength divided by two.
Chebyshev order: order uses acosh of the attenuation ratio divided by acosh of the frequency selectivity ratio.
Butterworth order: order uses the logarithmic attenuation ratio divided by twice the logarithmic selectivity ratio.
Loss estimate: total loss combines conductor loss and dielectric loss. The result is multiplied by resonator length and order for a quick cascade estimate.
Unloaded Q: Q is estimated from phase constant divided by twice the attenuation constant.
How To Use This Calculator
- Select the filter type. Choose band pass, low pass, or high pass.
- Enter passband and stopband frequencies in MHz.
- Select Chebyshev when ripple is acceptable. Select Butterworth for a smoother passband.
- Enter target impedance, dielectric constant, and ground plane spacing.
- Add copper thickness, loss tangent, and conductivity for loss estimates.
- Leave manual order as zero for automatic order selection.
- Use trim percent when your layout needs manufacturing correction.
- Press the calculate button. Results appear above the form.
- Use CSV or PDF export for records, reports, or design comparison.
Stripline Filter Planning Guide
Stripline filters are useful when a board needs controlled impedance, shielding, and repeatable radio performance. The signal trace is buried between two reference planes. That structure reduces radiation and protects nearby circuits. It also makes the dielectric constant more important than air loading.
Why Geometry Matters
The trace width sets the characteristic impedance. A wider trace lowers impedance. A thinner dielectric also lowers impedance. This calculator estimates the first layout width from target impedance, dielectric constant, and plane spacing. It is a starting point, not a final signoff. Final layouts should still be tuned with field solving and measurement.
Frequency And Length
Distributed filters use physical line length as part of the circuit. A quarter wavelength resonator is compact and common in band pass structures. A half wavelength resonator is longer, but it can suit different coupling styles. The calculator converts frequency into guided wavelength. It then applies the selected resonator mode and optional trim.
Order And Selectivity
Filter order shows how many resonant sections may be needed. Higher order designs reject unwanted signals better. They also need more board area, tighter coupling, and better manufacturing control. Chebyshev response gives sharper rejection for a defined ripple. Butterworth response gives smoother passband behavior with slower rolloff.
Loss And Q
Loss comes from conductor resistance and dielectric heating. Thin copper, narrow traces, high frequency, and lossy material increase insertion loss. The estimated unloaded Q helps compare materials and stackups. Higher Q normally means lower loss and cleaner selectivity.
Cost View
Finance teams often need a quick layout estimate before fabrication. Board count and cost per board give a simple project cost line. This does not replace quoting. It helps compare substrate choices, order changes, and prototype options before a purchase decision.
FAQs
What is a stripline RF filter?
It is a filter made from transmission line sections buried between two ground planes. The structure supports controlled impedance, reduced radiation, and stable behavior in compact RF layouts.
Is this calculator suitable for final manufacturing?
It is best for early planning and comparison. Final manufacturing should include electromagnetic simulation, tolerance review, fabrication notes, and measured prototype tuning.
What does ground plane spacing mean?
It is the distance between the two reference planes around the stripline trace. This value strongly affects trace width and impedance.
Why does dielectric constant matter?
Dielectric constant changes wave speed inside the board. Higher values shorten wavelength and reduce physical resonator length for the same frequency.
What does manual order override do?
It lets you force a chosen resonator count. Use zero when you want the calculator to estimate order from ripple and stopband attenuation.
Why is loss only an estimate?
Real loss depends on copper roughness, plating, via transitions, housing effects, coupling gaps, and fabrication tolerance. This tool uses simplified planning formulas.
Should I use quarter wave or half wave resonators?
Quarter wave sections save area and are common in compact filters. Half wave sections are longer and may fit different coupling or layout needs.
Can I export my results?
Yes. Use the CSV button for spreadsheet work. Use the PDF button for a quick printable report.