Modified compact combline bandpass filters are proposed based on the miniaturized quarter-wave transmission line which is composed of the parallel coupled line and lumped capacitors. The electrical length of the parallel coupled line in a resonator, which determines the size of combline bandpass filters, is just 5°or 7°, resulting in a compact circuit area. The designed combline bandpass filter also has a wide upper stopband by suppressing the spurious passbands, not moving. Measured results of two fabricated filters centered at 400MHz show good agreement with the theoretical predications.
1. Introduction
2. Limitations of Stepped-Impedance Resonat or Filters
3. Miniaturization of Quarter-Wave Transmission Line
4. Bandpass Filter Design
5. Simulation and Fabrication
6. Conclusion
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