Microstrip synthesis

Interdigital bandpass filter

Quarter-wave bars grounded at alternating ends. Compact and steep, with a wide spurious-free window above the passband.

indicative Response is indicative — geometry is the deliverable The interdigital response uses the textbook bandwidth-carrying inverter form, not Matthaei's Table-II J/Y_A coupling data. It puts the centre frequency in the right place and the bandwidth roughly right, and it is not geometry-faithful. Use the dimensions and the export; treat the plotted curve as a sanity check, not a prediction.

Specification

Centre frequency (GHz)

0.1 – 40 GHz.

Fractional bandwidth

0.10 means a 10 % passband. Above about 0.2 the coupled-line gaps get very tight — the fab check will tell you.

Order (sections)

Number of resonators. Higher is steeper and lossier.

Response

Passband ripple (dB)

Chebyshev only. 0.1 dB is a common choice for a clean passband; 0.5 dB buys steeper skirts.

System impedance (Ω)

Substrate

Permittivities are datasheet design values.

What you get

Enter a specification and press Synthesize. Every result includes:

Physical dimensions — widths, gaps and lengths in millimetres
A drawn layout, to scale
The predicted response, with the honesty label above attached to it
A manufacturability check against a real Australian shop's process envelope
The models used and the range over which they are valid
A KiCad footprint and a DXF you can take straight to CAD

Nothing is stored against you, and the result page has a shareable address.