Miniaturized RF reconfigurable bandpass filter with dynamic wideband frequency and constant bandwidth tuning capability

The paper presents a high selective reconfigurable band pass filter that has an adjustable center frequency and a constant absolute bandwidth tuning. The proposed filter has been designed through a multimode resonator-based approach, with two interdigitally coupled structures creating the passband. In order to realize frequency tuning, there are two varactor diodes incorporated. This filter has a small size that assures little bandwidth variation in a wide tuning. As well, the coupling structure equivalent circuit is given to further analyze. This has been experimentally verified by demonstrating that the proposed filter has a number of benefits that include easy implementation, large range of tuning, broad center frequency agility, and small size. A tunable prototype working in the range of frequencies 4.7–5.9 GHz was designed and experimented. Center-frequency agility is also observed with different constant absolute bandwidths of between 600 MHz and 2.3 GHz with a tuning ratio of up-to 3.8:1. The proposed filter was also able to have tuning along center frequencies without changing the absolute bandwidths which was 1.1 GHz. The change in the insertion loss (S21) was nearly independent of tuning, within the tuning range of 300 MHz, at the range of 4.6–5.9 GHz to 4.9–6.0 GHz. The filter proposed had an insertion loss of approximately 0.8 dB at passband. The results of the experiment are in agreement with the Equivalent Circuit model and simulation, which confirms the effectiveness of the proposed design.