Patent ID: 6864758

Claim:
An apparatus comprising: a plurality of ports; a first quarter-wavelength transmission line comprising a first end electrically coupled to a first port of said plurality of ports and a second end electrically coupled to a second port of said plurality of ports; a first resonant circuit electrically coupled from said first port to ground, said first resonant circuit comprising: a first varactor diode having a capacitance variable in response to an applied voltage; and a first transmission line in parallel with said first varactor diode; a second quarter-wavelength transmission line comprising a first end electrically coupled to a third port of said plurality of ports and a second end electrically coupled to said second port; a second resonant circuit electrically coupled from said third port to ground, said second resonant circuit comprising: a second varactor diode having a capacitance variable in response to an applied voltage; and a second transmission line in parallel with said second varactor diode; a third quarter-wavelength transmission line comprising a first end electrically coupled to a fourth port of said plurality of ports and a second end electrically coupled to said second port; a third resonant circuit coupled from said fourth port to ground, said third resonant circuit comprising: a third varactor diode having a capacitance capable of being varied in response to an applied voltage; and a third transmission line in parallel with said third varactor diode.