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Compact High-Q Bandpass Filter Using 3-D Stacked Stripline
Yu Cao1, Yong Liu1, Junling He1
1School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China.
Micromachines
|May 4, 2026
Summary
This study introduces a compact, high-Q bandpass filter (BPF) using a novel 3D stacked stripline design. The miniaturized filter achieves excellent performance, making it ideal for 5G and 5G-Advanced base stations.
Area of Science:
- Electrical Engineering
- Electromagnetics
- Microwave Engineering
Background:
- Miniaturization of filters is crucial for modern communication systems.
- Traditional filter designs often face trade-offs between size, performance, and spurious signal suppression.
- Achieving high unloaded Q-factor (Qu) and controllable transmission zeros (TZs) simultaneously is a significant design challenge.
Purpose of the Study:
- To present a novel compact high-Q bandpass filter (BPF) using a 3D stacked stripline configuration.
- To demonstrate the effectiveness of T-shaped stepped impedance resonators (SIRs) for miniaturization.
- To enable flexible placement of transmission zeros (TZs) through various cross-coupling schemes.
Main Methods:
- Utilized T-shaped stepped impedance resonators (SIRs) for miniaturization.
- Employed a U-shaped folding of the filter geometry to realize both broadside and edge coupling.
- Conducted a comprehensive analysis of electric and magnetic coupling structures.
- Designed, fabricated, and measured a tenth-order general Chebyshev BPF prototype centered at 3.485 GHz.
Main Results:
- Achieved a high unloaded Q-factor (Qu) of 1200 in a compact electrical size (0.58 × 0.23 × 0.19 λg³).
- Successfully implemented up to six transmission zeros (TZs) for enhanced selectivity.
- Demonstrated a spurious-free frequency range extending to 12 GHz.
- Measured insertion loss of 0.58 dB and return loss better than 20 dB within the passband.
Conclusions:
- The proposed 3D stacked stripline BPF offers excellent electrical performance, including high Q-factor and multiple TZs.
- The design's miniaturization and performance characteristics make it highly suitable for 5G and 5G-Advanced communication base stations.
- The U-shaped geometry effectively integrates broadside and edge coupling for versatile filter design.
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