GAUSSIAN SEAM-MODE CIRCUITS FOR, MILLIMETRE WAVELENGTHS

PhDAlthough the Maxwell equations govern the propagation of EM waves at all frequencies, the methods required to generate, direct, analyse and detect radiation differ from band to band. This thesis is concerned with the development and demonstration of 'Quasi-optical' techniques for millimetre wavelengths, which involve the propagation of Gaussian profiled beams a few wavelengths across, and the realization of a general circuit approach to mm-wave measurement. Gaussian beam-mode analysis, which is used in later chapters to understand propagation of quasi-optical beams, is reviewed in chapter 1. Chapter 2 outlines the design, manufacture and testing of corrugated feed horns which generate fundamental Gaussian beam-modes. The design and manufacture of lenses which control the spreading of the beams and directional couplers which provide desirable signal processing functions in quasi-optical circuits is discussed in chapter 3. Chapter 4 traces the development of a Faraday isolator which operates in free-space and can suppress unwanted reflections in quasi-optical circuits. Chapter 5 discusses a reusable circuit board upon which systems can be easily and quickly constructed. A null reflectometer built using quasi-optical components is outlined in chapter 6 and reflection measurements from lenses and horns presented. Chapter 7 describes a corrugated feed horn/lens antenna used in a balloon-borne nw-wave cosmic background experiment. Finally, Chapter 8 demonstrates the use of quasi-optical components in a 115 GHz receiver circuit

Compact corrugated feedhorns with high Gaussian coupling efficiency and -60 dB sidelobes

We demonstrate that very high performance, extremely compact, scalar corrugated feedhorns can be designed and constructed by optimizing the excitation and phasing of the HE11, HE12 and HE13 modes near the throat of the horn whilst limiting excitation of higher order modes. We present the design and measurement of two families of dual-profiled horn, both with a directivity of 20 dBi that couple with very high efficiency to a fundamental Gaussian mode. The first was optimized for sidelobe performance and features sidelobes approaching -60 dB for a horn length of only 15.6λ. The second was designed to minimize horn length and achieves sidelobe levels below -35 dB for a horn which is only 4.8λ long. The horns exhibit excellent coupling to the fundamental free-space Gaussian mode, with LG00 power coupling of 99.92% and 99.75% respectively. We demonstrate excellent agreement between simulation and experiment at 94 GHz and simulate the performance over a 20% bandwidth. High performance compact scalar horns are of interest because they reduce manufacturing risk at high frequencies, and reduce size and weight at lower frequencies, which can be important in horn arrays and space applications, where horn arrays often have serious weight and size restrictions.PostprintPeer reviewe

Intelligence within BAOR and NATO's Northern Army Group

During the Cold War the UK's principal military role was its commitment to the North Atlantic Treaty Organisation (NATO) through the British Army of the Rhine (BAOR), together with wartime command of NATO's Northern Army Group. The possibility of a surprise attack by the numerically superior Warsaw Pact forces ensured that great importance was attached to intelligence, warning and rapid mobilisation. As yet we know very little about the intelligence dimension of BAOR and its interface with NATO allies. This article attempts to address these neglected issues, ending with the impact of the 1973 Yom Kippur War upon NATO thinking about warning and surprise in the mid-1970s. It concludes that the arrangements made by Whitehall for support to BAOR from national assets during crisis or transition to war were - at best - improbable. Accordingly, over the years, BAOR developed its own unique assets in the realm of both intelligence collection and special operations in order to prepare for the possible outbreak of conflict

Terahertz Faraday Rotation of SrFe 12 O 19 Hexaferrites Enhanced by Nb Doping

From American Chemical Society via Jisc Publications RouterHistory: received 2022-07-21, rev-recd 2022-09-25, accepted 2022-09-26, pub-electronic 2022-10-04, asap 2022-10-04, issue-pub 2022-10-19Article version: VoRPublication status: PublishedFunder: National Natural Science Foundation of China; doi: 10.13039/501100001809; Grant(s): 12174146Funder: National Natural Science Foundation of China; doi: 10.13039/501100001809; Grant(s): 91963201Funder: China Scholarship Council; doi: 10.13039/501100004543; Grant(s): 201806370199Funder: Vedeck? Grantov? Agent?ra M?VVa? SR a SAV; doi: 10.13039/501100006109; Grant(s): 2/0034/23Funder: Vedeck? Grantov? Agent?ra M?VVa? SR a SAV; doi: 10.13039/501100006109; Grant(s): 2/0038/20Funder: Higher Education Discipline Innovation Project; doi: 10.13039/501100013314; Grant(s): B2006The magneto-optical and dielectric behavior of M-type hexaferrites as permanent magnets in the THz band is essential for potential applications like microwave absorbers and antennas, while are rarely reported in recent years. In this work, single-phase SrFe12–x Nb x O19 hexaferrite ceramics were prepared by the conventional solid-state sintering method. Temperature dependence of dielectric parameters was investigated here to determine the relationship between dielectric response and magnetic phase transition. The saturated magnetization increases by nearly 12%, while the coercive field decreases by 30% in the x = 0.03 composition compared to that of the x = 0.00 sample. Besides, the Nb substitution improves the magneto-optical behavior in the THz band by comparing the Faraday rotation parameter from 0.75 (x = 0.00) to 1.30 (x = 0.03). The changes in the magnetic properties are explained by a composition-driven increase of the net magnetic moment and enhanced ferromagnetic exchange coupling. The substitution of the donor dopant Nb on the Fe site is a feasible way to obtain multifunctional M-type hexaferrites as preferred candidates for permanent magnets, sensors, and other electronic devices

Compact corrugated feedhorns with high Gaussian coupling efficiency and -60 dB sidelobes

We demonstrate that very high performance, extremely compact, scalar corrugated feedhorns can be designed and constructed by optimizing the excitation and phasing of the HE11, HE12 and HE13 modes near the throat of the horn whilst limiting excitation of higher order modes. We present the designand measurement of two families of dual-profiled horn, both with a directivity of 20 dBi that couple with very high efficiency to a fundamental Gaussian mode. The first was optimized for sidelobe performance and features sidelobes approaching -60 dB for a horn length of only 15.6λ. The second was designedto minimize horn length and achieves sidelobe levels below -35 dB for a horn which is only 4.8λ long. The horns exhibit excellent coupling to the fundamental free-space Gaussian mode, with LG00 power coupling of 99.92% and 99.75% respectively. We demonstrate excellent agreement between simulation andexperiment at 94 GHz and simulate the performance over a 20% bandwidth. High performance compact scalar horns are of interest because they reduce manufacturing risk at high frequencies, and reduce size and weight at lower frequencies, which can be important in horn arrays and space applications,where horn arrays often have serious weight and size restrictions

Terahertz Faraday Rotation of SrFe₁₂O₁₉ Hexaferrites Enhanced by Nb Doping

From Crossref journal articles via Jisc Publications RouterHistory: epub 2022-10-04, issued 2022-10-04Article version: VoRPublication status: PublishedFunder: Vedeck? Grantov? Agent?ra M?VVa? SR a SAV; FundRef: 10.13039/501100006109; Grant(s): 2/0034/23, 2/0038/20Funder: China Scholarship Council; FundRef: 10.13039/501100004543; Grant(s): 201806370199Funder: National Natural Science Foundation of China; FundRef: 10.13039/501100001809; Grant(s): 12174146, 91963201Funder: Higher Education Discipline Innovation Project; FundRef: 10.13039/501100013314; Grant(s): B200