Design of a Low-Loss microstrip Lowpass-Bandpass triplexer with closely spaced channels for modern RF communication systems.

This study presents a new microstrip triplexer designed to simultaneously deliver precise lowpass and bandpass filtering functionalities for closely spaced frequency channels. Engineered to operate proficiently at three distinct frequencies, which are 1.02 GHz, 1.6 GHz, and 2.35 GHz where the proposed device demonstrates exceptionally low insertion losses of 0.4 dB, 0.19 dB, and 0.11 dB, respectively, validated rigorously through the simulations and practical measurements. Leveraging meticulous mathematical modelling, the primary structure behaviour and optimal operational frequencies are effectively identified, enabling precision tuning and significant miniaturization of the design. Subsequently, advanced optimization techniques are employed to refine the dimensions and performance, achieving optimal channel separation despite the closely spaced frequency bands. A physical prototype is meticulously fabricated and subjected to comprehensive S-parameter measurement analyses using a high-accuracy 2-port Vector Network Analyzer. The measured data closely aligns with the simulation and theoretical results, underscoring the accuracy and reliability of the proposed design methodology. The remarkably compact footprint, approximately 0.02 λg², positions this triplexer ideally for integration into advanced RF systems demanding stringent size constraints, such as 5G mid-band communication platforms and wireless energy harvesting applications. Ultimately, this work showcases a novel, compact, and high-performance solution capable of addressing critical challenges in spectrum efficiency and simultaneous multi-band operations in densely populated frequency environments.