A Novel Tunable Dual-Band Bandstop Filter (DBBSF) Using BST Capacitors and Tuning Diode
Thottam S. Kalkur
A novel approach to design Tunable Dual Band Band-Stop filters will be presented in this paper. These filters have a new configuration which have a coplanar microstrip line loaded with Stepped-Impedance 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 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, without needing to design new circuits. Thus, this approach leads the circuits to become smaller, increases the efficiency of the circuits, and reduces the costs. The filters were designed with notch frequencies at 1.5 GHz and 3.5 GHz, and then loaded respectively with Tuning Diode or BST capacitors, to compare their performance. The filter circuits were simulated with an Agilent ADS and Matlab program and were fabricated on FR-4 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.