2P · rfsynth Microwave synthesis

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Microstrip synthesis

Interdigital bandpass filter

Quarter-wave bars grounded at alternating ends.

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

The band edges of the passband. Centre frequency is their geometric mean, not their average.
0.1 – 40 GHz.
0.10 means a 10 % passband. Above about 0.2 the coupled-line gaps get very tight, and the fab check will tell you.

= 4.7 GHz centre, 10 % bandwidth

Number of resonators. Higher is steeper and lossier.
Chebyshev only. 0.1 dB is a common choice for a clean passband; 0.5 dB buys steeper skirts.
Permittivities are datasheet design values, transcribed by hand. Check them against the current datasheet before you commit copper.

What reaches the engine

Type over any of these and the laminate becomes custom. tan δ does not reach the response, which is lossless; it decides whether this page warns you about a lossy laminate. εr, h and copper thickness all reach the microstrip solution. 1 oz copper is 0.035 mm.

What you get

Enter a specification and press Synthesise. 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 six real process envelopes: Lintek in Australia, PCBWay and JLCPCB
  • The models used and the range over which they are valid
  • A KiCad footprint and a DXF you can take straight to CAD
  • A parametric CST macro, on the three bandpass filters

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