Ahmed Fayyadh H, Saad Rola, Khamas Salam K
Communications Research Group, Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S1 3JD, UK.
Micromachines (Basel). 2024 Jan 17;15(1):142. doi: 10.3390/mi15010142.
A novel quasi-twisted miniaturized wideband branch line coupler (BLC) is proposed. The design is based on bisecting the conventional microstrip line BLC transversely and folding bisected sections on double-layered substrates with a common ground plane in between. The input and output terminals, each with a length of λ/4, and the pair of quarter-wavelength horizontal parallel arms are converted into a Z-shaped meandered microstrip line in the designed structure. Conversely, the pair of quarter-wavelength vertical arms are halved into two lines and transformed into a periodically loaded slow-wave structure. The bisected parts of the BLC are placed on the opposite side of the doubled-layer substrate and connected through four vias passing through the common ground plane. This technique enabled a compact BLC size of 6.4 × 18 mm, which corresponds to a surface area miniaturization by ~50% as compared to the classical BLC size of 10 × 23 mm at 6 GHz. Moreover, the attained relative bandwidth is 73.9% (4.6-10 GHz) for S11, S33, S21, and the phase difference between outputs (∠S21 - ∠S41). However, if a coupling parameter (S41) of up to -7.5 dB is considered, then the relative bandwidth reduces to 53.9% (4.6-10 GHz) for port 1 as the input. Similarly, for port 3 as the input, the obtained bandwidth is 75.8% (4.5-10 GHz) for S33, S11, S43, and the phase difference between outputs (∠S43 - ∠S23). Likewise, this bandwidth reduces to 56% (4.5-8 GHz) when a coupling parameter (S23) of up to -7.5 dB is considered. In contrast, the relative bandwidth for the ordinary BLC is 41% at the same resonant frequency. The circuit is constructed on a double-layered low-cost FR4 substrate with a relative permittivity of 4.3 and a loss tangent of 0.025. An isolation of -13 dB was realized in both S and S demonstrating an excellent performance. The transmission coefficients between input/output ports S, S, S, and S are between -3.1 dB to -3.5 dB at a frequency of 6 GHz. Finally, the proposed BLC provides phase differences between output ports of 90.5° and 94.8° at a frequency of 6 GHz when the input ports 1 and 3 are excited, respectively. The presented design offers the potential of being utilized as a unit cell for building a Butler matrix (BM) for sub-6 GHz 5G beamforming networks.
本文提出了一种新型准扭曲小型化宽带分支线耦合器（BLC）。该设计基于将传统微带线BLC横向平分，并将平分后的部分折叠在双层基板上，中间有一个公共接地平面。在设计结构中，长度均为λ/4的输入和输出终端以及一对四分之一波长的水平平行臂被转换为Z形曲折微带线。相反，一对四分之一波长的垂直臂被减半为两条线，并转换为周期性加载的慢波结构。BLC的平分部分放置在双层基板的相对侧，并通过四个穿过公共接地平面的过孔连接。这种技术使BLC的尺寸紧凑至6.4×18 mm，与6 GHz时10×23 mm的经典BLC尺寸相比，表面积缩小了约50%。此外，对于S11、S33、S21以及输出端之间的相位差（∠S21 - ∠S41），所获得的相对带宽为73.9%（4.6 - 10 GHz）。然而，如果考虑高达 -7.5 dB的耦合参数（S41），则以端口1为输入时，端口1的相对带宽降至53.9%（4.6 - 10 GHz）。同样，以端口3为输入时，对于S33、S11、S43以及输出端之间的相位差（∠S43 - ∠S23），所获得的带宽为75.8%（4.5 - 10 GHz）。同样，当考虑高达 -7.5 dB的耦合参数（S23）时，该带宽降至56%（4.5 - 8 GHz）。相比之下，普通BLC在相同谐振频率下的相对带宽为41%。该电路构建在相对介电常数为4.3、损耗角正切为0.025的双层低成本FR4基板上。在S和S中均实现了 -13 dB的隔离，表现出优异的性能。在6 GHz频率下，输入/输出端口S、S、S和S之间的传输系数在 -3.1 dB至 -3.5 dB之间。最后，当分别激励输入端口1和3时，所提出的BLC在6 GHz频率下输出端口之间的相位差分别为90.5°和94.8°。所提出的设计具有作为构建用于低于6 GHz 5G波束成形网络的巴特勒矩阵（BM）的单元的潜力。
