(Received: 23-Jan.-2022, Revised: 14-Mar.-2022 , Accepted: 6-Apr.-2022)
In this article, a single-layered 3 dB/45° coupler (Design D) is proposed for fifth-generation (5G) beamforming networks using cross-slotted patch topology, dumbbell-shaped slots, loaded stubs, notches and rectangular ground slots. The proposed Design D coupler is capable of eliminating the need for additional 45° phase shifters in the beamforming networks such as Butler matrix, which provides the main contribution in this work, especially in size reduction and bandwidth enhancements. The fractional bandwidths of 28.90%, 39.14% and 35.91% for -10 dB of |S11|, -3 dB ± 1 dB of |S31| and 5° phase imbalance of output phase difference are achieved by the proposed Design D coupler. The bandwidth enhancements of -3 dB ± 1 dB coupling coefficient, S31 and 45° ± 5° output phase difference for the proposed Design D coupler are 22.52% and 23.14% compared to Design A coupler, respectively. The bandwidth of 45° ± 5° output phase difference is increased by 16.3% owing to the presence of rectangular ground slots in Design D compared to Design C coupler. The patch size of the proposed Design D coupler is 0.22 λg x 0.23 λg. The electrical size of the proposed Design D coupler is reduced by 45.72% compared to Design A coupler.

[1] I. A. Rumyancev and A. Korotkov, "Survey on Beamforming Techniques and Integrated Circuits for 5GSystems," Proc. of the IEEE International Conference on Electrical Engineering and Photonics(EExPolytech), pp. 76-80, St. Petersburg, Russia, 2019.

[2] Federal Communications Commission, "Unlicensed Use of the 6 GHz Band, Notice of ProposedRulemaking," Federal Registers, pp. 31997-32002, Washington, D.C, 2020.

[3] H. Nachouane, A. Najid, A. Tribak et al., "Broadband 4 × 4 Butler Matrix Using Wideband 90° HybridCouplers and Crossovers for Beamforming Networks," Proc. of the International Conference onMultimedia Computing and Systems (ICMCS), pp. 1444-1448, Marrakec, Morocco, 2014.

[4] D. N. A. Zaidel, S. K. A. Rahim and N. Seman, "4 × 4 Ultra-Wideband Butler Matrix for Switched BeamArray," Wireless Personal, vol. 82, no. 4, pp. 2471-2480, 2015.

[5] S. F. Ausordin, S. K. Abdul Rahim, N. Seman, R. Dewan and B. Sa’ad, "A c3.3ompact 4 × 4 ButlerMatrix on Double-layer Substrate," Microwave and Optical Technology Letters, vol. 56, no. 1, pp. 223-229, 2013.

[6] R. Liang, Y. Zhang, W. Yan et al., "A Novel Design of Miniaturized Butler Matrix," Proc. of the 18thInternational Conference on Communication Technology (ICCT), pp. 560-563, Chongqing, China, 2018.

[7] K. Han, W. Li and Y. Liu, "Flexible Phase Difference of 4 × 4 Butler Matrix without Phase-shifters andCrossovers," International Journal of Antennas and Propagation, pp. 1-7, 2019.

[8] B. Li, Y. Chen, Z. Fu et al., "Substrate-guided Wave Optical True-time-delay Feeding Network forPhased-array Antenna Steering," Proc. of the International Society of Optics and Photonics (SPIE), pp.256-265, San Jose, CA, United States, 2000.

[9] F. Casini, R. V. Gatti, L. Marcaccioli et al., "A Novel Design Method for Blass Matrix BeamformingNetworks," Proc. of the 37th European Microwave Conference (EuMA), pp. 1512-1514, Munich,Germany, 2007.

[10] P. Chen, W. Hong, Z. Kuai and J. Xu, "A Double Layer Substrate Integrated Waveguide Blass Matrix forBeamforming Applications," IEEE Microwave and Wireless Components Letters, vol. 19, no. 6, pp. 374-376, 2009.

[11] W. Y. Lim and K. K. Chan, "Generation of Multiple Simultaneous Beams with a Modified Blass Matrix,"Proc. of the Asia Pacific Microwave Conference (APMC), pp. 1557-1560, Singapore, 2009.

[12] T. Djerafi, N. J. G. Fonseca and K. Wu, "Broadband Substrate Integrated Waveguide 4 × 4 Nolen MatrixBased on Coupler Delay Compensation," IEEE Transactions on Microwave Theory and Techniques, vol. 59, no. 7, pp. 1740-1745, 2011.

[13] F. E. Fakoukakis and G. A. Kyriacou, "Novel Nolen Matrix Based Beamforming Networks for Series-fed Low SLL Multibeam Antennas," Progress in Electromagnetics Research, vol. 51, pp. 33-64, 2013.

[14] D. M. Pozar. Microwave Engineering, 4th Edn., New York: John Wiley & Sons, Inc., 2012.

[15] C. Gai, Y. Jiao and Y. Zhao, "Compact Dual-band Branch-line Coupler with Dual Transmission Lines,"IEEE Microwave and Wireless Components Letters, vol. 26, no. 5, pp. 325-327, 2016.

[16] W. Feng, Y. Zhao, W. Che et al., "Dual-/Tri-Band Branch Line Couplers with High Power DivisionIsolation Using Coupled Lines," IEEE Transactions on Circuits and Systems II: Express Briefs, vol. 65,no. 4, pp. 461-465, 2018.

[17] L. Piazzon, P. Saad, P. Colantonio et al., "Branch-line Coupler Design Operating in Four ArbitraryFrequencies," IEEE Microwave and Wireless Components Letters, vol. 22, no. 2, pp. 67-69, 2012.

[18] A. M. Zaidi, M. T. Beg, B. K. Kanaujia et al. "A Dual Band Branch Line Coupler with Wide FrequencyRatio," IEEE Access, vol. 7, pp. 25046-25052, 2019.

[19] L. Xia, J. Li, B. A. Twumasi et al. "Planar Dual-band Branch-line Coupler with Large Frequency Ratio,"IEEE Access, vol. 8, pp. 33188-33195, 2020.

[20] C. Gai, Y. C Jiao and Y. L. Zhao, "Arbitrary Power Division Quadrature Branch-line Coupler withHarmonic Suppression," Microwave and Optical Technology Letters, vol. 60, no. 1, pp. 256-260, 2017.

[21] H.-R. Ahn and M. M. Tentzeris, "Arbitrary Power-division Branch-line Hybrids for High-performance,Wideband and Selective Harmonic Suppressions from 2fo," IEEE Transactions on Microwave Theoryand Techniques, vol. 67, no. 3, pp. 978-987, 2019.

[22] H.-J. Yoon and B.-W. Min, "Two Section Wideband 90° Hybrid Coupler Using Parallel-coupled Three-line," IEEE Microwave and Wireless Components Letters, vol. 27, no. 6, pp. 548-550, 2017.

[23] A. Bekasiewicz, "Miniaturized Dual-band Branch-line Coupler with Enhanced Bandwidth," Microwaveand Optical Technology Letters, vol. 61, no. 6, pp. 1441–1444, 2019.

[24] U. Dilshad, C. Chen, X. Chen et al., "Broadband Quadrature Hybrid for Image Rejection in Millimeter-wave Receivers," Proc. of 16th International Bhurban Conference on Applied Sciences and Technology(IBCAST), pp. 975-978, Islamabad, Pakistan, 2019.

[25] J.-G. Chi and Y.-J. Kim, "A Compact Wideband Millimeter-wave Quadrature Hybrid Coupler Using Artificial Transmission Lines on a Glass Substrate," IEEE Microwave and Wireless Components Letters, vol. 30, no. 11, pp. 1037-1040, 2020.

[26] W. Yangsheng, H. Fuping and K. Dewu, "Design of Broadband Planar Magic-T Using 3-dB Branch-lineCoupler and Phase Shifter," Proc. of the 3rd Asia-Pacific Conference on Antennas and Propagation, pp.81-83, Harbin, China, 2014.

[27] D. Letavin, S. Shabunin and D. Trifonov, "Investigation of the Connection of Additional Stubs to thePhase Shifter Based on the Directional Coupler," Proc. of the 2019 Ural Symposium on BiomedicalEngineering, Radioelectronics and Information Technology (USBEREIT), pp. 364-367, Russia, 2019.

[28] S. S. Hesari and J. Bornemann, "Design of a SIW Variable Phase Shifter for Beam Steering AntennaSystems," Electronics, vol. 8, no. 9, pp. 1-14, 2019.

[29] W. Zhang, Z. Shen and S. J. Xuk, "A Compact Wideband Phase Shifter Using Slotted Substrate IntegratedWaveguide," IEEE Microwave and Wireless Components Letters, vol. 29, no. 12, pp. 767-770, 2019.

[30] S. Liu and F. Xu, "Novel Substrate-Integrated Waveguide Phase Shifter and Its Application to Six-portJunction," IEEE Trans. on Microwave Theory and Techniques, vol. 67, no. 10, pp. 4167-4174, 2019.

[31] A. Singh and M. K. Mandal, "Arbitrary Coupling Arbitrary Phase Couplers with Improved Bandwidth,"IET Microwaves, Antennas & Propagation, vol. 13, no. 6, pp. 748-755, 2019.

[32] Y. Wu, L. Jiao, Q. Xue et al., "A Universal Approach for Designing an Unequal Branch-line Couplerwith Arbitrary Phase Differences and Input/Output Impedances," IEEE Transactions on Components,Packaging and Manufacturing Technology, vol. 7, no. 6, pp. 944-955, 2017.

[33] Q. He, C. Qi, C. Liu et al., "A Compact Arbitrary Power Division Coupler with Nonstandard PhaseDifference," Journal of Electromagnetic Waves and Applications, vol. 32, no. 3, pp. 293-305, 2017.

[34] S. A. Babale et al., "Single Layered 4 × 4 Butler Matrix without Phase Shifters and Crossovers," IEEEAccess, vol. 6, pp. 77289-77298, 2018.

[35] Y. -L. Li, Q. S. Liu, S. Sun and S. S. Gao, "A Miniaturised Butler Matrix Based on Patch Hybrid Couplerswith Cross Slots," Proc. of the IEEE Antennas and Propagation Society International Symposium(APSURSI), pp. 2145-2146, Orlando, FL, USA, 2013.

[36] M. Moubadir, H. Aziz, N. A. Touhami and A. Mohamed, "A Miniaturized Branch-line Hybrid CouplerMicrostrip for Long Term Evolution Applications," Procedia Manufacturing, vol. 22, pp. 491–497, 2018.

[37] P. Upadhyay, V. Sharma and R. Sharma, "Design of Microstrip Patch Antenna Array for WLANApplication," Int. J. of Engineering and Innovative Technology (IJEIT), vol. 2, no. 1, pp. 295-297, 2012.

[38] Y. S. Wong, S. Y. Zheng and W. S. Chan, "Quasi-arbitrary Phase-difference Hybrid Coupler," IEEETransactions on Microwave Theory and Techniques, vol. 60, no. 6, pp. 1530-1539, 2012.

[39] Y. Wu, J. Shen and Y. Liu, "Comments on “Quasi-arbitrary Phase-difference Hybrid Coupler”," IEEETransactions on Microwave Theory and Techniques, vol. 61, no. 4, pp. 1725-1727, 2013.

[40] S. Sun and L. Zhu, "Miniaturised Patch Hybrid Couplers Using Asymmetrically Loaded Cross Slots," IET Microwaves, Antennas & Propagation, vol. 4, no. 9, pp. 1427-1433, 2010.