The detection of partial discharge (PD) activities in high-voltage equipment can be conducted according to several mechanisms of signal detection, including electromagnetic wave signal detection, acoustic signal detection, chemical reactions, electrical signal detection, and optical emission detection. Recently, multiple methods of detection and localization of partial discharge activities, which occurred in power transformers and gas-insulated switchgear (GIS), have been proposed to monitor the health condition of high-voltage equipment, especially when the awareness regarding preventive maintenance has been emphasized at the industrial level and among electrical providers. In aligning the needs of the industrial sector and the improvement of PD-detection methods, this manuscript focuses on reviewing the current practice methods for the detection and localization of PD signals in high-voltage equipment, comparing their efficacy, and summarizing the future direction of research work-related methods of PD detection. The comparative reviews are discussed in terms of the mechanism of PD signal detection, indication parameters, calibration techniques, and the advantages and limitations of each method of PD measurement in detail.

Beamforming networks for multiple beam antennas are believed to be in the vanguard of technological developments in mmWave for 5G wireless applications. The basic idea of beamforming technique is the application of multiple antenna elements radiating the same signal at an identical phase and wavelength, into one strong signal pointed to a specific direction. For low cost and power consumption, radio frequency beamforming networks (RF-BFNs) such as Blass matrices, Butler matrices, and Nolen matrices will play a critical role in achieving the ever-increasing demands in wireless technology. Therefore, this study aims to present a comprehensive survey and developments of RF-BFNs with (particular focus in Butler matrices). From the fundamental perspectives of the beamforming techniques and progress over time, component evolution includes branch-line coupler (BLC), Phase shifter (PS), and Crossovers to complete system Butler matrix (BM) integration. Different design techniques to improve bandwidth, size reduction, multi-band, and other performance characteristics are discussed extensively. Furthermore, the paper also discusses different geometry of Butler matrices in open microstrip transmission lines, substrate integrated waveguide (SIW) and gap waveguide (GWG) technologies highlighting key developments and research challenges from single band to dual-band operations. We expect this paper to provide more profound insights into the designs processes and suggest suitable ways to facilitate further developments of RF-beamforming networks at mmWave and sub-mmWave frequency ranges.

This paper introduces an innovative 4×4 dual-band Butler matrix (BM) characterized by compactness and an enhanced frequency ratio (K). The design employs meandered lines and an interdigital capacitor unit cell based composite right/left-handed transmission-line (CRLH-TL) metamaterial (MTM) structure. The BM integrates compact dual-band 3 dB branch-line couplers (BLC), a 0 dB crossover, and a dual-band 45° phase shifter on a single Rogers RT5880 substrate (with ε _r = 2.2 and h = 0.787 mm). Simulations and measurements results demonstrates reflection and isolation coefficients exceeding -20 dB at all ports, with a obtained insertion loss of -6±3 dB over the 0.7 GHz and 3.5 GHz frequency bands. The achieved phase differences of ±45°, ±135°, ±135°, and ±45° indicate a maximum average phase tolerance of ±4.5°. Importantly, the BM’s overall dimensions are 140 mm × 192 mm, resulting in a 78% size reduction compared to traditional BM designs. The proposed configuration is designed and simulated using CST Microwave Studio, with the agreement between simulated and measured parameters highlighting design reliability and effectiveness. Additionally, a performance evaluation comparing the proposed BM with existing circuits reveals its suitability for sub-6 GHz 5G dual-band antenna array beamforming networks (BFN) due to its compact size and improved band ratio.

Detection of partial discharge (PD) activities in high-voltage equipment can be done according to the several mechanisms of signal detection, which are electromagnetic wave signal detection, acoustic signal detection, chemical reactions, electrical signal detection, or optical emission detection. Recently, multiple methods of detection and localization of partial discharge activities occurred in power transformers and gas-insulated switchgear (GIS) have been proposed to monitor the health condition of high-voltage equipment, especially when the awareness regarding preventive maintenance has been emphasized at the industrial level and electrical providers. In aligning the needs of industrial and the improvement of PD detection methods, this manuscript focused on reviewing the current practice methods for the detection and localization of PD signals in high-voltage equipment and comparing their efficacy, in summarizing the future direction of research work-related methods of PD detection. The comparative reviews are discussed in terms of the mechanism of PD signal detection, indication parameters, calibration technique, advantages, and limitations of each method of PD measurement in detail.

The key elements used for receiving and processing signals in communication systems are the bandpass filters. Initially, a common operating mechanism was applied for the design of broadband filters, i.e., by cascading low-pass filters or high-pass filters using multiple line resonators with length quarter-half- or full-wavelength with central frequency, but using these approaches, the design topology becomes expensive and complex. The above mechanisms can be possibly overcome using a planar microstrip transmission line structure due to its simple design fabrication procedure and low cost. So, pointing out the above problems in bandpass filters such as low-cost, low insertion loss, and good out-of-band performance, this article presents a broadband filter with multifrequency suppression capability at 4.9 GHz, 8.3 GHz, and 11.5 GHz using a T-shaped shorted stub-loaded resonator with a central square ring coupled to the basic broadband filter. Initially, the C-shaped resonator is utilized for the formation of a stopband at 8.3 GHz for a satellite communication system, and then a shorted square ring resonator is added to the existing C-shaped structure for the realization of two more stopbands at 4.9 GHz and 11.5 GHz for 5G (WLAN 802.11j) communication, respectively. The overall circuit area covered with the proposed filter is 0.52 λg × 0.32 λg (λg is the wavelength of the feed lines at frequency 4.9 GHz). All the loaded stubs are folded in order to save the circuit area, which is an important requirement of next-generation wireless communication systems. The proposed filter has been analyzed using a well-known transmission line theory, even–odd-mode, and simulated with the 3D software HFSS. After the parametric analysis, some attractive features were obtained, i.e., compact structure, simple planar topology, low insertion losses of 0.4 dB over the entire band, good return loss greater than 10 dB, and independently controlled mutli stopbands, which make the proposed design unique and can be used in various wireless communication system applications. Finally, a Rogers RO-4350 substrate is selected for the fabrication of the prototype using an LPKF S63 ProtoLaser machine and then measured using a ZNB20 vector network analyzer for matching the simulated and measured results. After testing the prototype, a good agreement was found between the results.

This work presents a very compact microstrip lowpass-bandpass (LP-BP) triplexer, which is designed and analyzed based on a novel structure. Due to its complex design process, this type of triplexer is rarely designed. Compared to the previous LP-BP triplexers it has the most compact size of $0.006~\lambda _{\mathrm {g}}^{2}$ , whereas an LP-BP triplexer with dimensions smaller than $0.01~\lambda _{\mathrm {g}}^{2}$ has not been designed yet. This triplexer is designed based on a perfect mathematical method and optimization simultaneously. Its lowpass band has a cut-off frequency of 0.67 GHz, suitable for low-band 5G applications. The resonance frequencies of its bandpass channels are located at 2.15 GHz and 3.19 GHz. These bandpass channels make the proposed triplexer appropriate for 5G mid-band applications. This triplexer can suppress the harmonics from the first up to 8th harmonic. The bandpass channels are flat and wide with two fractional bandwidths (FBW) of 15% and 11.97%. To prove the designing process and its simulation results, the presented novel LP-BP triplexer is fabricated and experimentally measured. The comparison results show that the experimental measurement confirms the simulation results. The close alignment between the measurements and simulation results demonstrates a high level of accuracy of our designing method.