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Proposed is a compact dual-band balun filter adopting a double-sided parallel-strip line (DSPSL). The middle conductor plane can be treated as a virtual ground. Then, two sets of short-stub loaded dual-mode resonators on the top and the bottom layer act as two dual-band filters. They are fed by the DSPSL at the input port, and the filters can be excited simultaneously. Meanwhile, an out-of-phase feature is obtained between the two output ports. In addition, the proposed dual-band balun filter has good frequency selectivity which is due to multiple transmission zeros. Finally, a dual-band balun filter sample was designed and fabricated with good agreement obtained between its measured and simulated S-parameters.
(ProQuest: ... denotes formulae omitted.)
Introduction: In modern wireless and communication systems, a balun is a crucial component which can be used to convert signals between the unbalanced and the balanced components. Initially, we choose to cascade the balun and the bandpass filter directly with the aim of con- verting the signal between an unbalanced and a balanced circuit struc- ture with filtering selection. Undoubtedly, it will introduce high insertion loss and occupy large area. Therefore, integrating two separate circuit topologies into one device turns out to be a good idea. Over the past few years, several single-band passive devices exhibiting balun- type and frequency-selection functionalities have been proposed [1, 2]. However, little attention has been paid to the dual-band balun band- pass filter (BPF) [3, 4]. As mentioned in [3], the stepped-impedance half-wavelength and quarter-wavelength resonators were utilised to achieve a dual-band coupled-line balun filter while the dual-band balun BPF in [4] was implemented by a hybrid structure containing both microstrip and CPW resonators.
In this Letter, the double-sided parallel-strip line (DSPSL) has been applied to design a dual-band balun filter...