Abstract
In this letter, a novel hybrid microstrip and substrate-integrated defected ground structure (SIDGS) are proposed for filtering balun design. Coupled microstrip and SIDGS resonators can not only achieve 180° phase imbalance with filtering response but also realize wide stopband and wideband low radiation loss. In addition, the feature of stacked substrate packaging could reduce the size of the circuit and be flexible for integration. To verify this mechanism, a filtering balun operating at 3.08 GHz with 3-dB fractional bandwidth (FBW) of 45% is proposed based on hybrid microstrip and SIDGS, which exhibits the in-band amplitude- and phase-imbalances of ±0.5 dB and ±0.4°, respectively. The stopband extends to 18 GHz with the rejection level of 20 dB, whereas the measured total loss (i.e., including radiation, metal, and substrate loss) is less than 15% up to 15.3 GHz.
Highlights
W ITH the ever-increasing development of wireless systems, wideband interference suppression becomes a major challenge for the design of passive components
In [10] and [11], the substrate integrated waveguide (SIW) is applied to balun design with good in-band performance and low radiation loss, while it is limited by the narrow stopband and large size
A comparison of the filtering balun with the state-of-the-arts is shown in Table I, The proposed balun has merits of good in-band performance, wide stopband, wideband low radiation loss, and compact size
Summary
W ITH the ever-increasing development of wireless systems, wideband interference suppression becomes a major challenge for the design of passive components. In [10] and [11], the substrate integrated waveguide (SIW) is applied to balun design with good in-band performance and low radiation loss, while it is limited by the narrow stopband and large size. To extend the stopband bandwidth of balun, the stepped impedance resonators [12], stepped coupled lines [13], and high-order planar structure [14] are proposed. Substrate-integrated defected ground structure (SIDGS) [15], [16] is developed with wide stopband and wideband low radiation loss. The design of filtering balun with good in-band performance, wide stopband, and wideband low radiation loss, and compact size for flexible integration remains a great challenge. Such implementation can minimize the radiation loss in a wide frequency range and miniaturize the circuit size
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