High-Performance Microstrip Dual-Channel Filtering Coupler for IoT and Smart City Technologies

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Abstract
This paper presents the design, fabrication, and measurement of a microstrip 0° dual-channel coupler operating at 2.4/6.2 GHz. It is designed by utilizing two new resonators consisting of a hybrid of radial and meandering cells. The resonators are designed to be identical to obtain a 0-degree symmetrical coupler with balanced magnitudes and phases. The resonators are designed in a creative way to save space, with an overall size of only 0.041 λg2. An important advantage of this coupler is having an excellent filtering frequency response with high selectivity. Meanwhile, the harmonics are suppressed from DC up to 12.6 GHz with a maximum level of -14.7 dB and from DC up to 9.65 GHz with a maximum level of -20 dB. Also, it has low insertion losses and excellent return loss characteristics. At 2.4 GHz, the coupler exhibits a maximum group delay of 1 ns, with very low phase and magnitude imbalances of 0.54° and 0.083 dB, respectively. The values of S21, S31, and S11 at 2.4 GHz are -3.192 dB, -3.109 dB, and -30 dB, respectively, showing excellent insertion and return losses. Similarly, at 6.2 GHz, the coupler achieves a maximum group delay of 0.97 ns, maintaining low insertion losses and satisfactory return loss values. The compact design and working at 2.4 GHz demonstrate its suitability for integration into Internet of Things and smart city infrastructures, where reliable and efficient signal processing is crucial.

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