Design and Performance Analysis of a Diplexer for Simultaneous GSM and Bluetooth Communication

In this paper, we propose a novel diplexer structure connected to an antenna, enabling simultaneous operation of GSM/GPRS and Bluetooth bands. The compact design employs microstrip open-ended resonators to reject the Bluetooth band in the GSM/GPRS path and vice versa in the alternate path. The proposed structure is designed and simulated on a 10-mil FR-4 substrate. Measurement results confirm the functionality of the proposed diplexer, demonstrating insertion loss of less than 1 dB across all GSM/GPRS bands and providing at least 25 dB isolation from the Bluetooth band. By combining this structure with a dual-band antenna covering the GSM/GPRS/Bluetooth bands, we achieve improved range, directivity, and signal integrity. Additionally, this approach eliminates antenna length mismatch problems that are typically encountered with conventional monopole antennas in the Bluetooth bands.