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Symmetry is a key factor for Branch-Line Couplers (BLCs) in RF and microwave systems. This balanced approach evenly distributes power between two output ports, aiding impedance matching and reducing unwanted coupling and crosstalk, while increasing inputoutput isolation. Furthermore, the symmetrical design of BLCs ensures favorable return loss and phase balance, which are essential for phase-sensitive detectors and beamforming. This symmetry also guarantees consistent performance over a wide frequency range, making it suitable for broadband or multi-frequency applications. We present a compact BLC operating in two frequency bands, ideal for 5G sub-6 GHz applications. It uses Tshaped lines with folded lines and stubs in a Minkowski fractal shape, resulting in a size reduction of 90%. The design and simulation were performed using the CST Microwave Studio at 0.7 GHz and 3.5 GHz, achieving a new high frequency band ratio of 5. A prototype on Rogers RT5880 substrate (εr = 2.2, h = 0.787 mm) was tested to validate the design's effectiveness, offering potential for modern wireless applications requiring versatile frequency band operation. [ABSTRACT FROM AUTHOR]

The rapid development of 5G communication networks has ushered in a new era of high-speed, low-latency wireless connectivity, as well as the enabling of transformative technologies. However, a crucial aspect of ensuring reliable communication is the accurate modeling of path loss, as it directly impacts signal coverage, interference, and overall network efficiency. This review paper critically assesses the performance of path loss models in mid-band and high-band frequencies and examines their effectiveness in addressing the challenges of 5G deployment. In this paper, we first present the summary of the background, highlighting the increasing demand for high-quality wireless connectivity and the unique characteristics of mid-band (1–6 GHz) and high-band (>6 GHz) frequencies in the 5G spectrum. The methodology comprehensively reviews some of the existing path loss models, considering both empirical and machine learning approaches. We analyze the strengths and weaknesses of these models, considering factors such as urban and suburban environments and indoor scenarios. The results highlight the significant advancements in path loss modeling for mid-band and high-band 5G channels. In terms of prediction accuracy and computing effectiveness, machine learning models performed better than empirical models in both mid-band and high-band frequency spectra. As a result, they might be suggested as an alternative yet promising approach to predicting path loss in these bands. We consider the results of this review to be promising, as they provide network operators and researchers with valuable insights into the state-of-the-art path loss models for mid-band and high-band 5G channels. Future work suggests tuning an ensemble machine learning model to enhance a stable empirical model with multiple parameters to develop a hybrid path loss model for the mid-band frequency spectrum. [ABSTRACT FROM AUTHOR]

The reported work demonstrates the design and realization of an integrated mid-band (sub-6 GHz) and mmWave multiple input, multiple output (MIMO) antenna for 5G handheld devices. The proposed prototype consists of the two-port MIMO configuration of the mid-band antenna placed at the top and bottom of the substrate, while the 4-port mmWave MIMO antenna is placed sideways. The MIMO configuration at the top and bottom consists of a two-element array to achieve high gain at the mid-band spectrum, while the antennas placed sideways are optimized to cover the 5G-mmWave band spectrum. The overall dimensions of the board were selected the same as the of smartphones, i.e., 151 mm × 72 mm. The mid-band antenna has an operational bandwidth of 2.73 GHz, whereas the mmWave antenna has an impedance bandwidth of 3.85 GHz with a peak gain of 5.29 and 8.57 dBi, respectively. Furthermore, the design is analyzed for the various MIMO performance parameters; it was found that the proposed antennas offer high performance in terms of envelop correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG) and channel capacity loss (CCL) within operational range. A fabricated prototype was tested and measured results show strong agreement with predicted results. Moreover, the proposed work is compared with state-of-the-art work for the same applications to demonstrate its potential for targeted application. [ABSTRACT FROM AUTHOR]