Abstract
A balanced substrate integrated waveguide (SIW) filter is proposed by etching transverse slots on the top surface. The SIW structures between each two adjacent slots are resonators operating at TE $_{20\delta }$ mode for differential-mode (DM) operation and at TE $_{10\delta }$ and TE $_{30\delta }$ modes for common-mode (CM) operation. The proposed TE $_{20\delta }$ -mode resonator is much shorter than the traditional TE201-mode resonator, which causes the whole design to be compact and low loss. Furthermore, the strong electric coupling formed by slots make it have wider bandwidth when compared with the state-of-the-arts. A prototype is designed at 3.5 GHz with the size of $1.2\lambda _{\mathrm {d}} \times 0.83\lambda _{\mathrm {d}}$ ( $\lambda _{\mathrm {d}}$ is the wavelength in dielectric at the center frequency), the minimum insertion loss of 0.91 dB, the 3-dB fractional bandwidth (FBW) of 16%, and the FBW for 20 dB CM suppression of 79%.
Highlights
Balanced filters with differential-mode (DM) passband and common-mode (CM) suppression have been extensively studied, due to their high immunity for environmental noise, low electromagnetic interference, and easy connection to other balanced circuits or antennas
One method is based on the cascaded traditional substrate integrated waveguide (SIW) resonators, which operate at TE102 mode [1], TE102 and TE201 modes [2], or TE101 mode [3]
Transverse slots are etched on the top metal of SIW to achieve cascaded short-length TE20δ-mode resonators, which make the proposed filter have the features of compact size, the lowest loss, the widest bandwidth, and single-layer substrate
Summary
Balanced filters with differential-mode (DM) passband and common-mode (CM) suppression have been extensively studied, due to their high immunity for environmental noise, low electromagnetic interference, and easy connection to other balanced circuits or antennas. The method of using half-mode SIW resonator with microstrip-to-slot transitions [4] is proposed but with multilayer structure. The SIW balanced filter using quarter- mode SIW resonator [5] can further reduce the size, and the structure can be single-layer, but the insertion loss is not small. The associate editor coordinating the review of this article and approving it for publication was Yingsong Li. In this letter, transverse slots are etched on the top metal of SIW to achieve cascaded short-length TE20δ-mode resonators, which make the proposed filter have the features of compact size, the lowest loss, the widest bandwidth, and single-layer substrate. The analysis of the short-length SIW resonator is studied, and the working mechanism of DM and CM operation is analyzed to guide the design. The full-wave simulation is done by Computer Simulation Technology (CST)
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