Based on a novel right-angled triangle artificial line, a branch-line coupler is designed in this letter. The measured results indicate that the proposed branch-line operates at 0.975 GHz with a stopband bandwidth more than 15fc. Here, fc is the center frequency of the coupler. Importantly, the suppression levels in the stopband are better than 15 dB. Besides, its occupied size is about 23.18×22.5 mm2, which is only 16.5% of a traditional one at the same operating band. In practice, the proposed branch-line coupler can be used in compact systems which require good high-order harmonic suppression.
2. Coromina, J., J. Selga, P. Velez, J. Bonache, and F. Martın, "Size reduction and harmonic suppression in branch line couplers implemented by means of capacitively loaded slow-wave transmission lines," Microwave & Optical Technology Letters, Vol. 59, No. 11, 2822-2830, 2017.
3. Krishna, I. S., R. K. Barik, S. S. Karthikeyan, and P. Kokil, "A miniaturized harmonic suppressed 3 dB branch line coupler using H-shaped microstrip line," Microwave & Optical Technology Letters, Vol. 59, No. 4, 913-918, 2017.
4. Kumar, K. V. P. and S. S. Karthikeyan, "Miniaturized quadrature hybrid coupler using modified T-shaped transmission line for wide-range harmonic suppression," IET Microwaves, Antennas & Propagation, Vol. 10, No. 14, 1522-1527, 2016.
5. Mondal, P. and A. Chakrabarty, "Design of miniaturized branch-line and rat-race hybrid couplers with harmonics suppression coupling coefficient reconfigurable wideband branch-line coupler topology with harmonic suppression," IET Microwaves, Antennas & Propagation, Vol. 3, 109-116, 2009.
6. Kuo, J. T., J. S. Wu, and Y. C. Chiou, "Miniaturized rat-race hybrid coupler," IEEE Microwaves Wireless Compon. Lett., Vol. 17, No. 1, 46-48, 2007.
7. Koziel, S., P. Kurgan, and B. Pankiewicz, "Cost-efficient design methodology for compact rat-race couplers," Int J. RF Microwave Comput. Aided Eng., Vol. 25, No. 3, 236-242, 2015.
8. Selga, J., J. Coromina, P. Velez, A. Fernandez-Prieto, J. Bonache, and F. Martin, "Miniaturise harmonic-suppressed rat-race couplers based on slow-wave transmission lines," IET Microwaves, Antennas & Propagation, Vol. 13, No. 9, 1293-1299, 2019.