Suchergebnisse

Circular polarized (CP) antennas are well suited for long-distance transmission attainment. In order to be adaptable for beyond 5G communication, a detailed and systematic investigation of their important conventional features is required for expected enhancements. The existing designs employing millimeter wave, microwave, and ultra-wideband (UWB) frequencies form the elementary platform for future studies. The 3.4–3.8 GHz frequency band has been identified as a worthy candidate for 5G communications because of spectrum availability. This band comes under UWB frequencies (3.1–10.6 GHz). In this survey, a review of CP antennas in the selected areas to improve the understanding of early-stage researchers specially experienced antenna designers has presented for the first time as best of our knowledge. Design implementations involving size, axial ratio, efficiency, and gain improvements are covered in detail. Besides that, various design approaches to realize CP antennas including (a) printed CP antennas based on parasitic or slotted elements, (b) dielectric resonator CP antennas, (c) reconfigurable CP antennas, (d) substrate integrated waveguide CP antennas, (e) fractal CP antennas, (f) hybrid techniques CP antennas, and (g) 3D printing CP antennas with single and multiple feeding structures have investigated and analyzed. The aim of this work is to provide necessary guidance for the selection of CP antenna geometries in terms of the required dimensions, available bandwidth, gain, and useful materials for the integration and realization in future communication systems. ; This project has received funding from Universidad Carlos III de Madrid and the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant 801538. Also, this work was partially supported by RTI2018-095499-B-C31, Funded by Ministerio de Ciencia,Innovación y Universidades, Gobierno de España (MCIU/AEI/FEDER,UE).

Securitization theory (ST) makes an insightful and significant contribution to security studies. Through the use of discursive speech act, ST provides an innovative strategy for understanding the application of security's distinctive character and dynamics to any issue in order to make it a security issue. Valuable as the theory is to security studies, the subaltern appear missing in existing securitization analyses. Even when the subaltern are examined, for instance in critiques of classical ST, they are conceived and presented as passive, lacking agency, voice, and power, and suffering from security silence problem. ST's reliance on discursive speech act and focus on state political elite prevent it from capturing the subaltern and subaltern securitization process. Furthermore, while existing ST and critiques of securitization studies offer some direction regarding how the subaltern actors may securitize threats to their security, these perspectives are incidental and grossly underdeveloped. In order to resolve this problem, the current study takes a novel approach to securitization studies by investigating how subaltern actors engage in securitizing discourses and practices. By combining the Fanonian decolonial theory of emancipatory violence, where the nature of the (post)colonial context becomes visible with the theoretical insights of ST, the study shows that the subaltern are able to securitize using protest and violence. The subaltern use protest and violence to show their perception and identification of security threats, mobilize the subaltern audience, and challenge and confront the threatening subject – often times, the subaltern's significant audience – to ensure that action is taken on issues concerning subaltern security. In addition to discourse, therefore, protest and violence serve as the subaltern's instruments of political communication used by the subaltern to move issues beyond normal to the point of extraordinary politics. Consequently, protest and violence can force audiences – including the common people and the political elite – to imagine threats to subaltern security, typically perceived but sometimes real, and accept subaltern securitization moves, and where possible take actions that may amount to an alteration or a change in the order of things. Such change may either be in favour of subaltern's perception of security or not. To uncover the essential dynamics of subaltern securitization, this study synthesizes a version of decolonial theory with elements of existing ST and focuses on the subaltern actors from below the state in Nigeria, a non-Western, postcolonial context. The results reveal that subaltern securitization is possible when members of the subaltern successfully mobilize themselves to collectively identify (real or perceived) threat to their security and in so doing challenging and confronting the threat. This makes their security concerns an issue of priority. The study concludes that desirable as subaltern securitization may be, especially to the subaltern, there is a tendency for subaltern securitization to obfuscate the danger that may lurk around subaltern's attempts to securitize certain issues.