Georgy.Moshkin
Full Member level 5
I have a mixed substrate design. Problematic part is wavegude to microstrip transition (ro4003) through FR4 substrate. While designing I've used value around Er=5 (FR4 for 35GHz). It seems to be underestimated. In reality prototype's central frequency probably pulled down by few GHz, because Er is much higher. By slowly tuning 35GHz source down by 200MHz constant improvement is observed. Simulation shows, that similar poor results may be obtained only if FR4 Er is 7 or even more. Is it a good guess?