A Novel Design for a Planar Microstrip Triple Diplexer With Enhanced Selectivity Using Highly-Selective Bandpass Filters

Abstract

This paper presents a novel, compact, and cost-effective design for a planar microstrip triple diplexer. The design incorporates three high-selectivity bandpass filters to ensure excellent isolation between the three operating bands. Each filter is characterized by sharp attenuation skirts surrounding its passband, which further enhances isolation. Due to fabrication constraints, the maximum achievable fractional bandwidth is limited to 25%. As a demonstration, a triple diplexer with center frequencies of 1.8 GHz, 2.6 GHz, and 3.5 GHz was fabricated on a Rogers RO4003C substrate, with overall dimensions of 45 mm $\times 48$ mm. This design is particularly well-suited for mobile communication systems ranging from 3G to 5G NR. The close alignment between theoretical predictions and measured results validates the performance of the proposed circuit.

Keywords

• Bandpass filter
• diplexer
• triple diplexer