can substrate effect phase noise?

I have change my substrate from rogers 4003 to FR4 for my PLL i find degradation of phase noise by 2 to 3 dB

depends what the materal its made from is and modeled to be

but YES easily

forinstance how thick it is what its made from
if i used a crystaline sub then it would have different effectors at different places and different frequencies

sometimes properties like this are use both to build the chip and also make it impossible to xray fully many reason
but totaly yes

FR4 is a lossy substrate , which means that the quality factor of ur resonator will be less , and this will for sure affect VCO phase noise performance

Khouly

Khouly I am using Hittite MMIC for VCO. so the resonator is not on FR4.

what is the frequency of ur circuit


khouly

this MMIC have VCO at 13 Ghz and internel divide by 4 also. afte VCO my circuit is in rogers but VCO is solder on FR4 difinitalty at such high freq FR4 is very lossy but the length of trnasmission line on FR4 carrying such high freq is only 50 mil then after that i use rogers substrate to ampify the singnal and drive to mixer.

50 mil is very small , which is almost 1.3 mm , and the λ guide for the FR4 for 13 GHz , is about 1 cm , so the effect should be very small

i donot know , what is the reason for this drop , may be u need some matching before ur rogers circuit

khouly