you need not look for any example help for a varactor based filter simulation.
you just take a varactor spice model from alpha or aeroflex-metalics,enter
these parameters in ADS diode model. Use these diodes in place of capacitors
in your filter circuit. Donot forget to connect bias supply to these diodes,as they
need reverse biasing to function as varaibale capacitors.
Can I measure output reponse from the tuning circuit tht using Varactor diode without combining BPF? If so, wht components needed in tuning circuit besides varactor diode?