can anyone help me on design of patch with micromachining

hi
i am working on a rectangular patch on gallium arsenide substrate. the design uses selective etching of the substrate below the patch using micromachining. the feed is microstrip line and matching done with the help of inset.
but because the substrate has been etched the impedence is very hard to match.
any ideas
dipto

could you write down more information about the etching of the device?
i don't understand.. u r using wet or dry etching? .. LIGA process provides good ortho profiles with high height to width ratio

Yeah, I agree with the previous post. It's important to know what type of etching approach you're using. Is the inability of matching the impedance possibly due to over-etching of the substrate (or maybe the feed uline itself)?