A purely passive design technique for a class-J power amplifier (PA) is proposed, based on complex terminations at the fundamental frequency and the second harmonic, which increases the bandwidth ...while maintaining high efficiency. Using combined analytical derivation and numerical simulations, the drain impedance termination locus curve is obtained in the drain efficiency and DC voltage spaces. Successive application of the newly proposed de-normalization technique avoids the drain DC voltage manipulation used elsewhere. This is due to the resulting variable reactance of the output drain-source capacitor, optimal over a wide frequency range. Following the proposed procedure and the obtained optimal parametric space, a GaN HEMT-based PA is designed, fabricated, and tested displaying a very good agreement of the predicted and measured results.
Introduction/purpose: The work is based on the Rule of the Technical Service, the Law on Public Procurement, as well as on the experience gained in performing the duties of the Chief of Logistics in ...the Logistics Battalion of the Armed Forces. It contains the concept of Logistics Support and presents a part of the supply and maintenance system through Public Procurement in the Logistics Battalion of the Armed Forces. Methods: The theoretical system of supply and maintenance is very complex and consists of a number of elements, organizational units, as well as certain principles. During the implementation, it is necessary to take into account all the principles and adhere to the rules and instructions. Also important was the help of colleagues from the Armed Forces and other state institutions who are in relevant positions and are important for logistics support. Results: The final result of the work is a presentation of some activities performed by the logistics body in the battalion with a review of procurement under account 4252. In the final part of the paper, the emphasis is placed on the instructions which regulate and define the division of procurement in more detail, as well as on the implementation according to expenditure account 4252 on "ongoing maintenance and repair of equipment". Conclusion: During the preparation of the paper, the biggest difficulty was the change of various rules and laws. Some rules and literature were written in the 1970s, and are still in force. A proposal for further tendencies would be to define new rules and organizations based on the experience of the countries in the region where the system has taken root.
The orbital angular momentum (OAM or vortex) waves are expected to provide ten-fold and larger increases in wireless data rates, required for short-range communications within the beyond 5G and 6G ...concept of all-connected life and industry. We address the specifics of short-range communications employing OAM-carrying waves generated by small uniform circular arrays (UCAs) at lower, i.e., 10 GHz, transmission frequencies. Comparing the link budgets obtained using (i) asymptotic analytical formulas, (ii) numerical electromagnetic simulations, and (iii) measurements on two pairs of manufactured prototypes comprising 8 microstrip-patch-element UCAs, we point out the limitations of simplified models which do not account for various effects, such as coupling, parasitic radiation, and insertion loss. The observed effects are expected to be relevant at millimeter-wave frequencies as well.
Ethnobotanical survey presents the first step in the identification of new bioactive compounds. This study aimed to collect, document and analyse data on the traditional use of medicinal plants in ...Jablanica district (South-Eastern Serbia) and to compare traditional knowledge with scientifically proven data. Ethnobotanical study was carried out using semi-structured interviews with 103 informants. Discussion of the results was performed after the quantitative ethnobotany factors were calculated. Comparison of the data was done with those of European Medicines Agency (EMA), Yugoslav Pharmacopoeia 1984 (Ph. Jug. IV) and relevant scientific papers. The informants reported data on 89 medicinal plants belonging to 49 families in Jablanica district. The dominantly used families were
Lamiaceae
and
Asteraceae
, while
Hypericum perforatum L.
,
Mentha × piperita L.
and
Matricaria chamomilla L.
were the species with the highest number of use reports. The most frequently reported indications were respiratory, gastrointestinal, dermatologic, and psychological diseases. The species with most diverse uses were
Taraxacum campylodes G.E.Haglund, Achillea millefolium L.
and
Rosa canina L.
According to our results, medicinal plants in Jablanica district are mainly used for treating minor health issues as a mode of primary health care. The wide application of species belonging to
Lamiaceae
and
Asteraceae
families can be partially attributed to the fact that many cosmopolitan medicinal plant species belongs to these families and also to their predominance in the flora of Jablanica districts.
Systematic research of the ornithofauna of the Natural Monument "Lalinačka slatina" salt marsh has not been conducted so far, and data on some species of salt marsh birds are given only in the ...conservation study of this area. The first systematic surveys of ornithofauna were conducted in the period 2020-2021 with an emphasis on the nesting period of most species. The collected data were combined with data from the conservation study and indicated the presence of 72 bird species from 24 families and 12 orders. Migratory statuses have shown that the area is dominated by nesting birds, as many as 42 species have been recorded, as well as 24 species of strays, 5 species of wintering birds and 1 passer-by. Most of the bird species found in the "Lalinačka slatina" area are included in the various national and international lists, and are important considering the aspect of protection since they are endangered and rare.
Display omitted
•Detailed design space mapping for the combined graphene-metal waveguide resonators.•Design method to systematically achieve the specified tunable filtering response.•State-of-the-art ...full-wave numerical EM simulations and model parameter extraction.•Design curves for the combined graphene-metal filter tunability adjustment.•Fifth-order Chebyshev filter example and explanation of design trade-offs.
Tunable components and circuits, allowing for the fast switching between the states of operation, are among the basic building blocks for future communications and other emerging applications. Based on the previous thorough study of graphene based resonators, the design methodology for graphene tunable filters has been devised, outlined, as well as explained through an example of the fifth order filter. The desired filtering responses can be achieved with the material loss not higher than the loss corresponding to the previously studied single resonators, depending mostly on the quantity of graphene per resonator. The proposed design method relies on the detailed design space mapping; obtained data gives an immediate assessment of the feasibility of specifications with a particular filter order, maximal passband ripple level, desired bandwidth, and acceptable losses. The design process could be further automated by the knowledge based approach using the collected design space data.
Modern full-wave computational tools enable rigorous simulations of linear parts of complex microwave circuits within minutes, taking into account all physical electromagnetic (EM) phenomena. ...Non-linear components and other discrete elements of the hybrid microwave circuit are then easily added within the circuit simulator. This combined full-wave and circuit-based analysis is a must in the final stages of the circuit design, although initial designs and optimisations are still faster and more comfortably done completely in the circuit-based environment, which offers real-time solutions at the expense of accuracy. However, due to insufficient information and general lack of specific case studies, practitioners still struggle when choosing an appropriate analysis method, or a component model, because different choices lead to different solutions, often with uncertain accuracy and unexplained discrepancies arising between the simulations and measurements. We here design a reconfigurable power amplifier, as a case study, using both circuit-based solver and a full-wave EM solver. We compare numerical simulations with measurements on the manufactured prototypes, discussing the obtained differences, pointing out the importance of measured parameters de-embedding, appropriate modelling of discrete components and giving specific recipes for good modelling practices.
A novel radio frequency (RF) coil for ultra‐high‐field MRI in the form of a slotted waveguide array (SWGA) filled with a low‐loss high‐permittivity dielectric is proposed, evaluated, and ...demonstrated. A comprehensive computational electromagnetics study, along with basic RF measurements, to characterize the SWGA RF coil at 7T is presented. Slotted waveguides are robust structures capable of handling high powers. They are inherently narrow‐band and have well defined linear polarization. When arranged in an array, they effectively generate high‐quality B1 field with strong B1+ and extremely low B1− and Bz components. With added dielectric lenses, the observed transmit efficiencies exceed 2.3μTW in the human head model phantom, which is much higher than all results reported in literature. Moreover, we show that the proposed exciter, as an array with well‐decoupled elements (measured isolation between elements is 33 dB or higher), can effectively be used for RF shimming. The novel coil generates RF magnetic field with excellent circular polarization, good uniformity, and negligible axial z‐component, and it provides arbitrarily large or small field of view and excellent transmit efficiency, with and without dielectric lenses. It features well‐defined narrowband operation, excellent isolation between ports/channels, and inherent possibilities for field optimizations via RF shimming and parallel imaging.
PDF
