This paper demonstrates a matched bandstop resonator with a tunable K inverter. Two separated λ4 resonators are coupled through a tunable impedance inverter which consists of a varactor loaded microstrip T-shunt stub. In contrast to conventional K-inverter realizations, which possess narrowband properties, this paper demonstrates a physical realization of a novel tunable K-inverter using a varactor diode. Theoretical analysis together with the experimental results is presented in this paper. The optimum coupling value can be easily achieved by independently tuning the varactor where an enhanced notch response with 64dB attenuation is measured and shown in this paper.