# A Dual-Band Filter Using a Multimode Resonator with Asymmetrically Loaded Open-Circuited Stubs for Independent Passband Control

## TL;DR

This paper presents a new dual-band filter design for 5G systems using a resonator with open-circuited stubs to control two passbands independently.

## Contribution

The novel multimode resonator design enables independent dual-band control with high selectivity and isolation for 5G applications.

## Key findings

- The filter achieves a 2.6 GHz passband with 13.7 dB return loss and 0.37 dB insertion loss.
- A second passband at 4.8 GHz shows 23.6 dB return loss and 0.77 dB insertion loss.
- The design provides three transmission zeros for high selectivity and isolation in 5G systems.

## Abstract

A novel multimode resonator is designed in this paper. Incorporating two open-circuited stubs of distinct impedances loaded onto a uniform half-wavelength transmission line, the resonator enables the realization of a dual-band filter—with center frequencies at 2.6 GHz and 4.8 GHz—through both simulation and experimental measurement. Regarding the first passband centered at 2.6 GHz, the device exhibits a return loss |S11| of 13.7 dB, an insertion loss |S21| of 0.37 dB, and a 3 dB bandwidth of 17.3%. As for the second passband with a center frequency of 4.8 GHz, the measured return loss |S11| amounts to 23.6 dB, the insertion loss |S21| measures 0.77 dB, and the 3 dB bandwidth is recorded at 8.75%. Specifically designed for 5G communication systems, the filter achieves three transmission zeros by adopting electrical coupling and 0° feeding, resulting in high selectivity and high isolation. Practical measurements verify that the experimental results are consistent with the simulation results.