Design of Compact Quasi-Elliptic Bandpass Filters Based on Coaxial Inset Resonators

Design of Compact Quasi-Elliptic Bandpass Filters Based on Coaxial Inset Resonators

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This article reports a novel inset resonator configuration for coaxial filter applications with quasi-elliptic responses.The design and analysis of the inset resonator are discussed in detail and accurately modeled as a capacitively-loaded stepped-impedance half-wavelength resonator featuring more compactness, high quality factor, and enhanced Chelsea Boots spurious responses in comparison with conventional half-wavelength and combline resonators.Additionally, the operating frequency can be tuned intrinsically through the displacement of the coaxial resonator, eliminating the need for any additional tuning elements and maintaining a stable quality factor.Two quasi-elliptic inset resonator type filters are implemented in planar and longitudinal coupling configurations, respectively.

The first takes the form of a folded four-pole 2.93 GHz filter with two symmetrical transmission zeros.The fabricated filter has a compact structure of 29.76 cm 3, an insertion Giftwrap loss better than 0.

73 dB, a return loss better than 18 dB, and a wide spurious-free band up to $3.5cdot f _{0}$.The second inset-type quasi-elliptic filter is realized in a longitudinal inline arrangement.An example of a 2.

53 GHz three-pole filter is presented with a closely-positioned transmission zero, wide spurious-free band ( $approx 3cdot f _{0}$ ), and a very compact structure of $55.7 imes 33 imes 33$ mm 3.