Maybe I should make an example so we can better understand each other:
My design goal is a 0.5dB Chebyshev fc 1GHz, 7th order. 50ohm in, 50ohm out.
Using a 0.8mm (32mil) thick FR4 PCB (epsilon_r of 4.6). These impedances/TMLs were chosen.
Zo = 50ohm, 60mil wide, guided wavelength 162.5mm (effective epsilon_r 3.406)
Zc = 10ohm, 500mil wide, guided wavelength 146.8mm
Zl = 110ohm, 8mil wide, guided wavelength 175.5mm
The normalized filter coefficients are: 1.737, 1.258, 2.638, 1.344, 2.638, 1.258, 1.737
From the coefficients, I get this set of lumped element values: 5.5pF, 10nH, 8.4pF, 10.7nH, 8.4pF, 10nH, 5.5pF
So far so good. Now to calculate the uncompensated lengths:
L2 = L6 = 10nH = 17mm
L4 = 10.7nH = 18.4mm
C1 = C7 = 5.5pF = 8.3mm
C3=C5 = 8.4pF = 13mm
How should I compensate the lengths now? For each inductor (L2, L4, L6) should I use a sum of tangents of all capacitive elements from the filter?
Meaning the K in this case should be equal: K = Zc * ( 2*tan(pi*8.3mm/10) + 2*tan(pi*13mm/10) )
Am I right?
//UPDATE:
The compensating coefficient K for all capacitor lengths in the filter is 9.3025 ohms or thereabout (hope I calculated those tangents right).
After trying to compensate L2(L6) - the 10nH inductor, the new length is 14.2mm instead of 17mm. At least it seems a legit number, not some strange bullshit.