my frequency is 1.05GHz in the first passband and 2.0GHz in the second passbandA varactor is tuned with a variable voltage. Your circuit does not have a variable voltage and I do not see an inductor.
What frequency?
To see a schematic of your design would answer a lot of questions.I have designed a dualband bandpass filter with HFSS
below is the HFSS design. I only used the HFSS software to designTo see a schematic of your design would answer a lot of questions.
yes, the varactor is between the resistor and the resonatorApparently you are driving the varactor through a resistor. Where the ground return for the (anode?)?
no please, I only have a ground for the resonator, but not a DC path per seIs there a DC path through the resonator to ground?
ok, thanksYou need the DC path to tune the diode. No path -- no tuning.
Check ARRL handbook for varactor circuits and application
http://www.arrl.org/arrl-handbook-2020
You can find older versions on Amazon or other sites. Really old ones from the 1930's might command a premium price.
the path i only have a patch that is from the resistor to the ground. but the diode is fixed between the resistor and the resonator please. I really like your inputs, carry me on Sir, help me. I need to hand in my thesisOr to put it another way, how can you have DC voltage across the diode if the circuit is open?
ok thanksHere is an article with example circuits
https://www.electronics-notes.com/a...de/varactor-varicap-diode-circuits-design.php
The varactor mus have a DC path to Ground
ok, let me be humble and tell my problem. I don't actually know how to apply the bias to the varactor, I would be glad if I am helped on how to design the bias circuit. currently, I only removed the modeled resistor from the HFSS design and I was able to tune the frequencies, but I doubt if that will be correct for fabrication. please teach me hoe to do it. I would be very thankfulKjeldgaard has the main point. Progress in helping you will be more and more difficult if not impossible without a schematic. Anything we can read will be find.
How are you applying bias to the varactor?
by Jake Hertz
by Jake Hertz
by Jake Hertz