LAUSR

This paper introduces a balanced (differential) multiband reconfigurable (tunable) bandstop filter (BSF) using all lumped elements. The main features of the design include its ultra-compact size as well as flexibility to control any frequency band independently in terms of both center frequency and absolute bandwidth (ABW). In the proposed structure, the corresponding non-resonating nodes (NRN) of the symmetrical bisections are connected to N number of LC π-circuits (N-band cell) through capacitors. Again, in each symmetrical bisection, K number of NRNs are series cascaded through LC π-circuits. This results in a Kth order N-band stopband (notch) response in differential mode (DM) operation whereas provides a passband response when excited by a common mode (CM) signal. Reconfiguration of any DM stopband is obtained by using tunable capacitors for the corresponding LC π-circuit in each N-band cell and also, for its coupling capacitors to the NRNs. To validate the proposed topology, a dualband differential tunable BSF is designed and fabricated where both DM stopbands are controlled independently in the range of 1.16 GHz–1.32 GHz. Also, the bandwidth of each band is varied independently by 20–50 MHz without affecting the other band. At any tuning state, DM stopband rejection for each band is found to be ≥ 19 dB, resulting in a minimum CMRR value of 19 dB. The fabricated prototype occupies an area of 0.13λg × 0.04λg (21mm × 7 mm) where λg is the guided wavelength at the center frequency of the entire spectral range, and the experimental results show a good agreement with the simulation results.