A Novel Tunable Dual-Band Bandstop Filter (DBBSF) Using BST Capacitors and Tuning Diode

A novel approach to design Tunable Dual-Band Band-Stop filters will be presented in this paper. These filters have a new configuration with a coplanar microstrip line loaded with SteppedImpedance Resonators (SIRs). These can be tuned by using tuning elements such as a tuning diode and ferroelectric capacitor. The Dual-Band Band-Stop Filter (DBBSF) and Dual-Band Band-Pass Filter (DBBPF) have become the most attractive circuit components in modern communication devices. Several studies have been done in this area but without tuning. Tuning is important in these circuits because the same circuit could be used in multiple band frequencies by applying a voltage, thus eliminating the need to design new circuits. This approach leads to smaller circuits with higher efficiency and reduced costs. The filters were designed with notch frequencies at 1.5GHz and 3.5GHz, and then loaded respectively with Tuning Diode or BST capacitors to compare their performances. The filter circuits were simulated with an Agilent ADS and Matlab program and were fabricated on FR4 substrates. By loading the resonators with BST capacitors or tuning diodes, with no DC applied voltage, the first and second notch frequency shifts significantly. The application of DC bias to these varactors changes the center frequencies of the dual band filter.