Multifunctional Bandpass Filters With Reconfigurable and Switchable Band Control

A new series of multifunctional reconfigurable bandpass filters (BPFs) and their analytical synthesis design are presented in this paper. They feature frequency-adaptive characteristics in both their passbands and notched bands, as well as switchable-notched-band capability. Their basic filter architecture is discussed and modeled in a progressive manner. The initial circuit consists of a second-order Chebyshev-type filter to which two stubs are added to increase filtering selectivity through transmission-zero (TZ) creation. Subsequently, to produce an embedded notched band, stubs acting as band-stop structures are also inserted at the input-output terminals. The multifunctional properties of this filter scheme are analyzed attending to the resonance frequencies of the introduced stubs. When these resonance frequencies are tuned while keeping a constant spacing between them, a center-frequency reconfiguration with constant bandwidth is achieved; when the resonance frequency of the notched band is shifted to the TZ positions, the notched band is switched-off. The described filter synthesis methodology is based on the constant and frequency-mapping technique, where the dual-mapping functions are controlled to obtain reconfigurable/switchable properties from a low-pass prototype. For experimental-validation purposes, two reconfigurable lumped-element filter prototypes using the proposed synthesis technique are designed, manufactured, and tested. One exhibits a simple reconfigurable passband, whereas the other one adds a controllable/switchable embedded notched band that results in a quasi-elliptic-type dual-passband response. When compared to some related prior-art designs, these filters have the advantages of explicit design process, quantified analysis, and multifunctional responses.