Development of a Microstrip Triplexer with High Isolation for 5G Sub-6 GHz Applications

The rapid proliferation of multi-standard fifth-generation (5G) new radio sub-6 GHz systems has intensified the demand for compact, high-isolation multiplexing components capable of simultaneously routing multiple frequency channels through a single shared antenna port without cross-band interference. This article presents the design and full-wave electromagnetic (EM) simulation of a compact microstrip triplexer operating at 2.2, 2.6, and 3.0 GHz for 5G sub-6 GHz applications. The proposed triplexer employs square open-loop resonators (SOLRs) arranged as three independent three-pole Chebyshev bandpass filter channels. Each channel is synthesized from a standard normalized Chebyshev lowpass filter prototype. The three channels are integrated at a common input port via a T-junction, with the connecting transmission line stubs dimensioned to enforce high inter-channel isolation. The triplexer is implemented on Rogers RT/Duroid 6010LM substrate. Full-wave EM simulation results demonstrate return losses of 21.1, 23.1, and 22.8 dB; insertion losses of 1.08, 1.01, and 0.98 dB; and inter-channel isolations of 45.7, 45.2, and 45.7 dB for ports S32, S42, and S43, respectively. The achieved inter-channel isolation exceeding 45 dB represents a significant improvement over the majority of recently reported microstrip triplexers operating in the sub-6 GHz range. The device occupies a compact circuit area of 0.34λg × 0.52λg. λg is the guided wavelength for the microstrip line impedance at the 2.6 GHz centre frequency of the triplexer.