This article presents compact, scalable Gysel power combiners (PCs) in a rectangular coaxial (rectax) guide for high-power applications. Compared to corporate and radial PCs, the proposed Gysel PCs achieve a compact footprint while ensuring reliable high-power operation and scalability to higher order configurations. The proposed concept is validated through two different implementations of Gysel PCs. The first implementation employs the conventional TEM mode of a coaxial guide, while the second employs the microstrip-like quasi-TEM mode in modified rectax. It further reduces fabrication and assembly effort by minimizing the number of individual components required and can improve thermal performance by increasing the core metal volume/surface area in the PCs. In the first implementation, a Gysel PC is designed, fabricated, and measured at 1.87 GHz with a fractional bandwidth of 42%. In the second implementation, two-, four-, and six-way Gysel PCs operating at 2.9, 3.37, and 3.18 GHz are developed, exhibiting fractional bandwidths of 15.5%, 16.3%, and 27.35%, respectively, thereby validating the proposed design concept. To the authors’ knowledge, this is the first implementation of the Gysel PCs in the rectax guide.

This letter presents the design and development of a compact two-way Gysel power divider for high frequency (HF), very high frequency (VHF), and ultra high frequency (UHF) receiver applications. The proposed Gysel power divider achieves the miniaturization by employing ferrite-core transformers and ensures the reliable wideband operation with 1000:1 bandwidth. To validate the proposed concept, a prototype is designed, fabricated, and measured over the frequency range from 1 to 1000 MHz. The fabricated prototype exhibits a measured return loss better than 16.3 dB and isolation exceeding 18 dB over the band. The peak insertion loss is 0.8 dB, resulting in a peak combining efficiency of 84%. The average combining efficiency is better than 74% over the HF, VHF, and UHF bands. The measured amplitude and phase imbalances (PIs) are better than 0.4 dB and 0.3 degrees, respectively, over the entire band of operation. Furthermore, no nonlinearity is observed upto an input drive of 20 dBm.

This letter presents a six-way Gysel power combiner (PC) in a rectangular coaxial guide (rectax) for high-power applications. Compared to corporate and radial PCs, the proposed Gysel PC achieves a compact footprint while ensuring reliable high-power operation and scalability to higher order configurations. To validate the proposed concept, a Gysel PC is designed, fabricated, and measured at 1.87 GHz with a fractional bandwidth of 42%. The measured return loss is better than 15 dB, and the isolation exceeds 23 dB across the entire bandwidth. The peak insertion loss is approximately 0.1 dB, and the average combining efficiency remains better than 90% over the operating band. To the authors’ knowledge, this is one of the first implementations of the Gysel PC in the rectax guide.

A single-layer substrate integrated waveguide (SIW) filtering power divider (FPD) using a modified coupling matrix is presented in this paper. By employing four SIW resonator cavities with an iris structure for inter-resonator coupling and tapering for input/output coupling, a fourth-order FPD is designed, simulated, and fabricated using RT/Duroid5880 substrate (30 mils thickness) at 3.5 GHz with 150 MHz bandwidth. The functional integration of band pass filter (BPF) and power divider into a single multifunctional component has resulted in better in-band performance and component miniaturization. The design has provided the measured return loss better than 15 dB over the band. The measured amplitude and phase imbalances are within 0.04 dB and 1 degree respectively. To the best of the author's knowledge, this is the first coupling matrix-based FPD implemented in SIW technology, in which the design strategy is scalable to produce higher-order FPD systematically. In addition, any of the filter synthesis techniques can be adopted for designing the proposed FPD.

A systematic design approach to realize a multi-functional filtering power divider (FPD) in microstrip technology is demonstrated in this paper. The coupling matrix of the coupled resonator-based band-pass filter (BPF) is exploited to design the FPD. The FPD integrates the features of a BPF and a power divider (PD) into a multi-functional component. This enhances system performance by mitigating additional losses like cascaded mismatch loss. In-addition, it leads to reduced form factor due to functional integration. The proposed design methodology can be utilized to design the higher-order FPDs.

In this paper, we present a circularly polarized filtering conical horn antenna for aero-space communication applications. This filtering antenna basically includes the functionality of a band pass filter and a circularly polarized conical horn antenna within a single component. This not only leads to a small form factor (reduced size due to functional integration) but also eliminates additional losses like cascaded mismatch loss and hence enhancing the performance of the transceiver system. The proposed 4th order filtering antenna is realized at 11.2 GHz with a bandwidth of 350 MHz and realized gain of 8.1 dBi.

RF sources are vital components in numerous scientific and engineering pursuits related to wireless communication and sensing applications. However, state-of-the-art RF sources like analog signal generators and vector signal generators are expensive for educational purposes. This article describes a low-cost electronically tunable S- and X-Band continuous wave RF source for a microwave laboratory at the undergraduate and post-graduate levels. RF signals in the unlicensed industrial, scientific and medical (ISM) band (2.4 to 2.525 GHz) are generated directly using an inexpensive commercially available nRF24L01 transceiver module. The module is configured using an Arduino Uno microcontroller through a serial peripheral interface (SPI) protocol. Active frequency multiplication (by a factor of 4) is achieved using a HMC443LP4ETR MMIC chip from Analog Devices to convert the output to X-Band.

In this paper, we present a novel multifunctional filtering power divider (FPD) which is realized in coaxial technology for power combining applications. This FPD basically includes the functionality of a band pass filter and a power divider within a single component. This not only leads to a small form factor (reduced size due to functional integration) but also eliminates additional losses like cascaded mismatch loss thus enhancing the system performance. The proposed FPD is realized at 3.5 GHz with a fractional bandwidth of 4.3 %.

This paper presents the design and development of a compact E-plane sectoral waveguide power combiner at Ku-band operating from 13.6 GHz to 15.6 GHz. The proposed 4-way in-phase power combiner involves only 2 design parameters and achieves a measured return loss better than 15 dB. The measured amplitude imbalance and phase imbalance are within 0.65 dB and 6 degrees respectively. The total power combining efficiency is better than 82.5 % over the entire band of operation. The E-plane power combiner is proposed to be used in Ku-band satellite communication applications.

In this paper, two second-order electronically tunable bandpass filters are presented. The filters are implemented in microstrip technology using barium-strontium-titanate (BST) varactors and digitally tunable capacitors (DTC) for tuning the frequency response of the bandpass filters. The filter realized using BST varactors has a 35% tuning range from 900 MHz to 1.275 GHz with an insertion loss variation from 3.1 to 2.6 dB. The absolute bandwidth is nearly constant over the entire tuning range, varying from 64 to 72 MHz (around +/- 5% variation). The filter realized using DTCs also has a 36% tuning range from 850 MHz to 1.225 GHz with an insertion loss variation from 3.1 to 1.5 dB. The absolute bandwidth is constant over the tuning range, varying from 88 to 98 MHz (around +/- 5% variation). The bandpass filters are tuned using a single control signal. The tunable bandpass filters are proposed for use in reconfigurable radios.

This work proposes a novel active VHF/UHF monopole antenna for location and direction-finding applications. A nonfoster Active Matching Network (AMN) drives the designed ultrabroadband monopole's input for the enhancement of exclusive bandwidth operating from 60 MHz to 1.31 GHz (182.48% fractional bandwidth) with a 6 dB minimum return loss. Doublestage LNA is cascaded with AMN for the gain enhancement (≥ 40 dB) over the operating band. The AMN integrated monopole is extremely compact and ultra-miniaturized, with dimensions of 0.032λL×0.044λ L at 60 MHz. The measured results are in good agreement with the simulations. The authors believe that the ultrabroadband active monopole is one of the promising solutions for antenna arrays employed in direction-finding applications.

This paper presents the design and development of an 8-way 20kW co-axial radial power combiner (RPC) for high power S-band applications. The proposed 8-way in-phase RPC achieves a measured return loss better than 15 dB. The measured amplitude imbalance and phase imbalance are within +/- 0.25 dB and +/- 6 degrees respectively. The proposed RPC is capable of providing power of 20 kW at the combined port. The EM and thermal simulations are carried out to the validate the electrical and thermal performance of the RPC. The average power combining efficiency is better than 90% over the entire band of operation.

AbstractHydrogen is believed to be the most potential energy‐resources in the coming time due to its high energy density and zero greenhouse gas footprint. Among all types of hydrogen production processes, bio‐based hydrogen (biohydrogen) generation processes are found to be relatively cleaner than the other processes. In this review article current biohydrogen generation processes are critically reviewed to understand the critical factors associated with the hydrogen generation along with the challenges to be eliminated. In this review the factor like types of substrates, their pretreatment, bioreactor design, and other parametric influences on the overall biohydrogen production is discussed. Also, impact of different catalyst in hydrogen production has been discussed in this topic. The review indicated that most of the current hydrogen‐research are focused on the development of processes with high yield. However, one of the major drawbacks of biohydrogen process is purification of H2 from the gaseous mixture produced by microbial strains. To establish the biohydrogen production processes as promising as it considered to be there needs to have a robust purification system. Also, this review highlights that more rigorous research on the biohydrogen storage and its hazard analysis is necessary to meet the future expectation of hydrogen use in mass‐scale.

AbstractThis paper presents the design of novel compact multifunctional coaxial to waveguide power combining transition (PCT) for X‐band applications. For the proof of the proposed concept, 2‐way PCT operating over the entire X‐band (8.2–12.4 GHz) and 4‐way PCT operation from 9.5 to 10.8 GHz are designed, developed, and characterised. Two‐way PCT achieves a measured return loss better than 14 dB over the operating band, and the measured amplitude imbalance and phase imbalance are within 0.25 dB and 4°, respectively. Four‐way PCT achieves a measured return loss better than 15 dB over the operating band, and the measured amplitude imbalance and phase imbalance are within 1 dB and 10°, respectively. Furthermore, a 6‐way PCT is also designed, fabricated, and measured to demonstrate the scalability of the proposed concept. The 6‐way PCT achieves the measured return loss better than 15 dB from 9.9 to 10.475 GHz, and measured amplitude and phase imbalances are within 0.6 dB and 10°, respectively. The designed power combining transition is proposed to be used in X‐band applications like antenna array applications and power combining applications.

This article presents a systematic design methodology of novel multifunctional balun filters at 3.5 GHz for 5G and MIMO transceiver applications. The balun filters are realized using the modified coupling matrix of the coupled resonator-based bandpass filter. The balun filter integrates the functionality of balun and bandpass filter within a single filtering component, thus enabling system miniaturization (due to functional integration). In addition, it enhances the system performance by eliminating additional insertion loss and imbalance loss arising from the balun. For the proof of the concept, a fourth-order balun filter is designed, fabricated, and tested at a center frequency of 3.5 GHz with 150-MHz bandwidth (BW) in microstrip and coaxial technologies. The measured insertion loss is 1.5 and 0.5 dB, respectively. The rejection is better than 40 dB at +/- 300-MHz offset. The amplitude imbalance is within 0.2 and 0.4 dB, respectively. Finally, the phase imbalance is within 0.5 degrees and 2.5 degrees, respectively, over the entire BW. For the sake of completeness, a balun filter is also realized in rectangular waveguide technology at 10 GHz with 350-MHz BW. The proposed design methodology is scalable to realize higher order balun filters. The realized microstrip balun filter is tested in one of the channels of ZCU216 RF system on chip (RF SoC) for 5G and MIMO transceiver applications for validation.

The performance of a packed bed reactor (PBR) containing immobilized sulphate reducing bacteria for sulphate removal from wastewater, utilizing carbon monoxide (CO) as the sole electron donor, is demonstrated. The performance of the PBR system in terms of CO and sulphate removal efficiencies (%RECO and %REsulphate, respectively) was predicted using three parameters, i.e. the hydraulic retention time (HRT, h), inlet concentrations of CO (ICCO, mg/L) and sulphate (ICsulphate, mg/L). An artificial neural network (ANN) model with 3-14-2 topology was developed by training the experimental data through the Levenberg Marquardt (LM) algorithm. Using genetic algorithm (GA) with appropriate objective functions, optimal sets of inputs were obtained to ensure maximum RE at a minimum HRT. The ANN had an overall accuracy above 98%, with a correlation coefficient of 0.99 and a root mean square error of 1.66%, suggesting its good performance. The automation of sulphate-rich wastewater industry through GA identified solutions might be leveraged for efficient operation in terms of saving time and resources.

The economic viability of the camel in the current scenario can be ensured by improving its dairy potential. The study on the udder and teat characteristics of dromedary camel and understanding its relationship with milk yield and milkability can be of great value in establishing camel as a dairy animal. The present study was conducted on 45 lactating she-camels of four Indian camel breeds, viz., Bikaneri, Jaisalmeri, Kachchhi, and Mewari, stationed at ICAR-NRCC Bikaner, Rajasthan, India. The udder, teat, and milk vein measurements traits, factors affecting these traits and their relationship with milkability traits, were studied in hand-milked Indian dromedary camel. The means ± S.E. of teat lengths (TL), namely, left fore (LF), left rear (LR), right fore (RF), and right rear (RR), were observed as 52.21 ± 1.66, 58.52 ± 2.11, 50.13 ± 1.74, and 54.37 ± 1.82 mm, respectively. The means ± S.E. of teat diameter (TD), namely, left fore, left rear, right fore, and right rear teat diameters, were observed as 42.44 ± 1.60, 46.01 ± 1.68, 39.29 ± 1.31, and 45.20 ± 1.56 mm, respectively. The means ± S.E for udder depth, udder length, udder height from the ground, milk vein diameter, and milk vein length were observed as 25.44 ± 0.42, 37.29 ± 0.80, 114.80 ± 0.80, 2.02 ± 0.08, and 88.70 ± 0.96 cm, respectively. Udder and milk vein measurements did not differ significantly between breeds. Kachchhi breed has largest teat length and diameter. The breed differences were significant (p ≤ 0.05) for TL-LF, TL-RF, and TD-RR only. The effect of parity was non-significant on udder, teat, and milk vein measurement traits except TD-RR (p ≤ 0.05); however, second parity animals had higher values for all the studied traits except udder height from ground. Positive and highly significant (p ≤ 0.01) correlation of milk yield was observed with the majority of udder, teat, and milk vein measurements, milking time, and milk flow rate, while a negative correlation was found with udder height from ground and milk let-down time. It can be concluded that udder characteristics are influenced by various genetic and non-genetic factors and its relationship with milk yield and milkability can be used for selection and dairy management purposes.

Background: Attention-deficit/hyperactivity disorder (ADHD) is marked by inattention, hyperactivity, and impulsivity. Experimental studies have reported increased theta activity and reduced beta activity on electroencephalography (EEG), although theta wave tends to appear during meditative, drowsy, hypnotic, or sleeping states. Aims: We aimed to study EEG changes in children with significant severity of ADHD. Settings and Design: A cross-sectional study was designed for the children with ADHD presenting to the Child and Adolescent Psychiatry Outpatient Department (OPD) of IHBAS. Methodology: A total of 33 ADHD children in the age group of 5–12 years attending OPD were included in the study after qualifying the inclusion and exclusion criteria for the study. DSM-5 criteria were used to make the diagnosis of ADHD and severity was assessed using Conners' Rating Scale-Revised Parent short version. The children with more than 50% score on the Conners Scale were included in the study. The quantification of the recorded EEG was done using Fast Fourier Transformation by New Natus NeuroWorks computer software. Statistical Analysis: The data were analyzed using SPSS version 23.0. Results: Around 3/4th of participants in the study showed elevated theta: beta ratio results on qEEG. Conclusions: Although ADHD is marked by inattention, hyperactivity, and impulsivity, children with ADHD showed marked elevated theta: beta ratio indicating raised slow-wave changes in cortical activity, thus concluding quantitative EEG as a promising biomarker in children with ADHD.

Biological sulfide precipitation by sulfate reducing bacteria (SRB) is an emerging technique for the recovery of heavy metals from metal contaminated wastewater. Advantages of this technique include low capital cost, ability to form highly insoluble salts, and capability to remove and recover heavy metals even at very low concentrations. Therefore, sulfate reduction under anaerobic conditions has become a suitable alternative for the treatment of wastewaters that contain metals. However, bioreactor configurations for recovery of metals from sulfate rich metallic wastewater have not been explored widely. Moreover, the recovered metal sulfide nanoparticles could be applied in various fields such as solar cells, dye degradation, electroplating, etc. Hence, metal recovery in the form of nanoparticles from wastewater could serve as an incentive for industries. The simultaneous metal removal and recovery can be achieved in either a single-stage or multistage systems. This paper aims to present an overview of the different bioreactor configurations for the treatment of wastewater containing sulfate and metal along with their advantages and drawbacks for metal recovery. Currently followed biological strategies to mitigate sulfate and metal rich wastewater are evaluated in detail in this review.

Industrial effluent are the major sources of heavy metal pollution and it is released into fresh waterbodies. Catla catla and Clarias batrachus were exposed to Nickel and Chromium for 24, 48, 72 and 96 hrs. The median lethal concentration (LC50) of nickel to Catla catla and Clarias batrachus for 96 h of exposure were 5.77 mg/l and 7.595mg/l, respectively. The median lethal concentration (LC50) of chromium to Catla catla and Clarias batrachus for 96 h of exposure were 16.468 mg/l and 34.476 mg/l, respectively. The result also revealed that mortality rate depends upon concentrations of heavy metals and duration of exposure. The acute toxicity levels were derived from LC50 concentrations of the heavy metals. Both the heavy metals produced lethality at smaller doses. Physiological responses like rapid opercular movement and frequent gulping of air was observed during the initial stages of exposure after which it became occasional. All these observations can be considered to monitor the quality of aquatic eco system and severity of pollution.