The paper presents a new design of a compact branch-line coupler (BLC) operating at 3.5 GHz, that is suitable for 5G applications. In order to miniaturize the proposed coupler, two miniaturization methods are combined where a T-shaped structure is used instead of quarter wavelengths parallels, as well as open stubs are introduced into the series lines resulting in a size reduction of 52.56% with 25.05% fractional bandwidth (FBW). The frequency responses indicate that the presented coupler is able to operate at 3.04 GHz to 3.91 GHz with a low return loss and high isolation that is improved to -28.9 and -31.1 dB in 3.5 GHz, insertion loss and coupling of -3.6 dB and -3.5 dB, respectively, and a phase difference of about 90°±1°. The strong agreement of measurement and simulation results indicated the suitability of this proposed design for 5G microwave integrated circuits (ICs) that require a small size.

This paper presents a design and optimization approach for a tri-band miniature planar rectangular patch antenna structure for wireless mobile applications. The tri-band operation while maintaining a compact size has been achieved by introducing a defected ground structure (DGS) to control the surface current distribution on the patch antenna and consequently achieve multi-band operation. The geometry of the patch and the position of the DGS were optimized by a genetic algorithm to achieve the desired performance using a simple and miniature design with an area of 16 mm × 20 mm × 1.6 mm, an 82% reduction in the area occupied by a conventional single-band structure used in the optimization process. The proposed GA-optimised antenna provided tri-band operation with bandwidths for |?11| > 6 from 3.2 - 3.5 GHz, 5.5 - 5.9 GHz and 6.3 - 7.1 GHz. At the centre frequencies of 3.4, 5.7 and 6.7 GHz, the peak gains were 0.7, 1.76 and 2.93 dB, respectively. The optimally designed antenna is etched on an FR-4 substrate. Simulation and measurement results show good agreement, making the proposed structure a suitable candidate for mobile applications requiring small and multifunctional telecommunication devices.

This paper presents a compact rectangular patch hybrid coupler design which can be operated at dual resonant frequencies and is suitable for modern wireless applications. The dual-band functionality while maintaining practical compactness is achieved by introducing a series of parallel rectangular slots. The proposed design is optimized by the CST studio suite software and etched on the FR4 substrate. The good agreement between the simulated and measured frequency responses indicate that the presented coupler is capable of operating from 2.44 GHz to 3.1 GHz and from 5 GHz to 5.8 GHz, with fractional bandwidth of 24.44% and 14.8%, respectively, and a size reduction of 56.28%. The robust simulation results indicate that the proposed design is suitable for microwave integrated circuits (ICs) that require small size and dual functionality.

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