Ultra-Compact Low-Pass Spoof Surface Plasmon Polariton Filter Based on Interdigital Structure

Area of Science:

• Electromagnetics and Wave Propagation
• Metamaterials and Plasmonics
• Microwave Engineering

Background:

• Spoof surface plasmon polaritons (SSPPs) enable subwavelength waveguiding at lower frequencies.
• Traditional SSPP structures often require large footprints.
• Interdigital structures (IS) offer a potential method for miniaturizing electromagnetic devices.

Purpose of the Study:

• To design and validate an ultra-compact low-pass filter utilizing an interdigital structure (IS) within an SSPP framework.
• To investigate the impact of the IS on the asymptotic frequency and unit dimensions of SSPP structures.
• To achieve efficient passband transmission and high out-of-band suppression in a miniaturized filter.

Main Methods:

• Design of SSPP unit cells incorporating an interdigital structure.
• Electromagnetic simulations to analyze dispersion curves and filter characteristics.
• Fabrication and measurement of a prototype filter to validate simulation results.

Main Results:

• The interdigital structure effectively reduces the asymptotic frequency and unit dimensions of SSPP units.
• The designed filter exhibits efficient transmission from 0 to 5.66 GHz.
• Excellent out-of-band suppression exceeding 24 dB from 5.95 to 12 GHz was achieved.
• A measured cut-off frequency of 5.53 GHz and an ultra-compact size of 0.5 × 0.16 λ₀² were obtained.

Conclusions:

• The interdigital structure is a viable method for miniaturizing SSPP-based filters.
• The proposed IS-based SSPP filter offers a significant size reduction while maintaining high performance.
• This design provides a promising solution for compact low-pass filtering applications in microwave and millimeter-wave systems.