A Lowpass-Bandpass Triplexer With A New Microstrip Configuration and Compact Size for 5G and Energy Harvesting Applications

This research presents a novel microstrip configuration for a lowpass-bandpass triplexer. To design this triplexer, first a lowpass filter (LPF) with some empty spaces is designed. Then, two microstrip sections are embedded inside the empty spaces to create bandpass (BP) channels. Therefore, this triplexer occupies a very small size of
$0.003~\lambda \text{g}^{2}$
. A rigorous mathematical analysis and an optimization process are conducted to enhance the triplexer performance. The proposed triplexer features a lowpass (LP) channel cut-off frequency at 870 MHz with bandpass (BP) channels operating at 1.335 GHz and 2.055 GHz. The achieved insertion losses are 0.2 dB, 0.09 dB, and 0.04 dB for all LP and BP channels that are remarkably low, making our triplexer ideal for energy harvesting applications. All bands are flat with suitable group delays (GDs). Meanwhile, the BP channels are wide with 14.1% and 25.5% fractional bandwidths (FBWs) for the middle and upper channels respectively. Our triplexer suppresses the harmonics after the LP channel from the
$1^{st}$
harmonic up to
$3^{rd}$
harmonic. Fabrication and measurement of the proposed triplexer validate our designing method and the simulation results.