Abstract
In this paper, two implementations of reconfigurable bandwidth bandpass filters (BPFs) are demonstrated both operating at a fixed center frequency of 2.4 GHz. The proposed reconfigurable bandwidth filters are based on a square ring resonator loaded with λg/4 open-ended stubs that are permanently connected to the ring and converted to either 3λg/4 open-ended stubs or λg/2 short-ended stubs by means of positive-intrinsic-negative(PIN) diodes to implement two reconfigurable bandwidth states for each case. Due to the symmetrical nature of the design, even- and odd-mode analysis is used to derive the closed-form to describe the reconfigurable filters’ behavior. The switching between narrowband and wideband is achieved using PIN diodes. In the first implementation (λg/4 open-ended stubs to 3λg/4 open-ended stubs), a reconfigurable bandwidth bandpass filter is proposed where additional out-of-band transmission zeros are generated by integrating a λg/2 open-ended stub at the input port. In the second implementation (λg/4 open-ended stubs to λg/2 short-ended stubs), further improvement in the upper stopband is achieved by utilizing a pair of parallel coupled lines (PCLs) as feeding lines and a pair of λg/4 high impedance short-ended stubs implemented at the input and output ports. To verify the validity of the simulated results, the prototypes of the proposed reconfigurable filters were fabricated. For the first case, measured insertion loss is less than 1.8 dB with a switchable 3-dB fractional bandwidth (FBW) range from 28% to 54%. The measured results for the second case exhibit a low insertion loss of less than 1 dB and a 3-dB fractional bandwidth that can be switched from 34% to 75%, while the center frequency is kept constant at 2.4 GHz in both cases.
Highlights
With the rapid growth in the multi-band and multi-functional Radio Frequency (RF) wireless communication systems, reconfigurable/tunable bandpass filters (BPFs) play a vital role and have gained wide attention from the researchers
In [2], a reconfigurable BPF design is reported at a fixed operating frequency of 2.4 GHz based on λg /4 open-circuited stubs or λg /2 short-circuited stubs to design a reconfigurable bandwidth BPF that can be switched from 34% to 75% keeping center frequency fixed at 2.4 GHz
For improving the out-of-band response, parallel-coupled lines (PCLs) of filtering characteristics are further improved by integrating short-ended stubs of length λg /4 along with length λg/4 are connected at the input/output ports instead of uniform transmission lines
Summary
With the rapid growth in the multi-band and multi-functional Radio Frequency (RF) wireless communication systems, reconfigurable/tunable bandpass filters (BPFs) play a vital role and have gained wide attention from the researchers. In such RF systems, reconfigurable/tunable BPFs are thought to demonstrate good filtering performance with low insertion loss (IL), sharp rejection and wide out-of-band response. Novel structures of a terminated cross-shaped resonator for designing reconfigurable bandwidth BPF are presented in [13] but the tuning range of the reported topology is small. To validate the proposed designs, prototype filters were fabricated and measured
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