Is it possible to force zone to clearance lower than Netclass clearance?

[fred4u]

Hi KiCaders,
Is it possible to force zone to clearance to value lower than its Netclass clearance?
I’m doing some RF and I use Coplanar waveguides, which require me to set certain clearance to ground plane.
However there are structures I need to approach with clearances tighter than calculated RF-to-GND distance (compact packages), using copper Zones (for smooth track width changes).
But if I set a general RF clearance which is needed for a coplanar waveguide, my RF zones are not filled. I have tried to set their clearance to lower values, but they stop on the netclass value.
Any workaround for this?

[mf_ibfeew]

write a custom rule.
Maybe this project could help:
create_lines.zip (25.8 KB)

[glenenglish]

move to KIcad 8RC2, rules are much more sophisticated. No problem with specifying rules for CPW. I have done it. Just set a zone clearance rule for the netclass … easy Check the new doco for custom design rules :

(rule "zone clearance myCPW  "
(layer outer)
(condition " A.NetClass == 'myCPW' && B.Type=='zone'")
(constraint clearance (min 0.15mm)  (opt 0.15mm)  (max 2mm)))

you might need to add a rule area to that condition if you dont want it tight around component pads etc
or add a rule after it (higher priority) to apply to pads.
like

(rule "cpw  tracks"
(layer outer)
(condition " A.NetClass == 'HV' && B.Type=='zone' && A.Type=='Track'")
(constraint clearance (min 0.15mm)))

(rule "cpwnetclass  pads"
(layer outer)
(condition " A.NetClass == 'HV' && B.Type=='zone' && A.Type=='Pad'")
(constraint clearance (min 0.5mm)))

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[fred4u]

Thanks, I’ve got my homework now to do

[fred4u]

So the easiest solution to me was to use a specific name for the “tight RF” Zones, and then create a name-based custom rule to override the clearance for the “TIGHTRF” named zones to my desired smaller value - exactly as in mf_ibeew example. Thank you @mf_ibfeew @glenenglish for pointing me to the right direction.
I have also noticed that I can re-use my Zone name for multiple indepenedent zones, actually using these Zone names as a sub-Netclass for my custom rule.