varactor tunable filter

i need any papers , or articles about that , and is there a varactors in the makret work in this range

khouy

interesting problem. I doubt there are any packaged devices that are below their self (series) resonant point at this frequency but if you could tolerate the Q you could probably put a quarter wave in series and get a capacitor again :)

do u mean that with the varactor i connect a microstrip line to make it back as a capacitor

khouly

yes. I've never tried it, but it makes sense for narrowband operation that if you're shooting for a variable shunt capacitance, you can achieve the same with a variable inductance rotated through the smith chart with a quarter wave line.

I can't imagine that this would work *well* but I wouldn't rule it out.

it would certainly exhibit lower frequency notch where the whole mess went series resonant.

Again, it is probably not the best approach.... but I've struggled with this sort of question when considering the design of discrete VCOs and tunable filters above a few GHz.

Lance

yeah , i am facing it right now , i am doing my master in 8 GHz transiver for and i need to make tunable VCO and filter
i have made good microstrip resonator oscillator , i need to make it tunable ,

i am thinking about injection locking

khouly

MAacom does have varactors that will work in your frequency range , check for the MAXXX series. I have seen people using them up to 10GHz with reasonable resutls.

good , i have seen them it is ok

i am asking is there any techniques to design a varible matching netwrok

is there any documents about these issue

khouly

This is a quite a good joke. How much capacitance tunability do you expect from varactor for designing an 8Ghz filter ?

Well I have never come to any book that describes tunable matching networks, although I believe if u based your matching network to a filter topology and replace your capacitors with Varicaps you will get some tunning, I have done a similar thing for a phase shifter based on varicaps. The problem is that the varicap inductance parasitics will influence the behavior of your filter, maybe if you parallel the diodes you will reduce their inductors effect and get some more flexibility.