Magnonic Crystal with Strips of Magnetic Nanoparticles: Modeling and Experimental Realization via a Dip-Coating Technique

In this article, we describe a magnonic crystal formed by magnetite nanoparticles. The periodic strip-like structure of the nanoparticles was fabricated on the surface of thin yttrium iron garnet single-crystal film grown on a gallium–gadolinium garnet substrate via dip-coating techniques. It was shown that such periodic structure induces the formation of the bandgaps in the transmission spectra of magnetostatic surface spin-waves (MSSW). The structure was simulated by the transfer matrix method. Spin-wave detection has been carried out by using a pair of microwave antennas and a vector network analyzer.

Peter John Bell Clarricoats. 6 April 1932—17 January 2020

Peter Clarricoats made fundamental contributions as a microwave engineer in the fields of applied electromagnetics for microwave and optical waveguides, and microwave antenna feeds. Peter was also a pioneer of optical fibres, and established the theory of electromagnetic propagation on dielectric and ferrite structures. In the course of this, he discovered that such structures can, under some conditions, support ‘backward waves’ and that guides can propagate complex modes. Over 40 years of his academic career, Peter Clarricoats had numerous notable achievements, including pioneering designs for shaped reflectors, reconfigurable reflectors and especially corrugated horns for microwave antennas. The latter are now universally used in satellite ground stations and in spacecraft. He published what became standard reference texts on corrugated horns for microwave antennas, microwave horns and feeds. He served as vice-president of both the Institution of Engineering and Technology and the International Union of Radio Science, and from 1998 to 2000 was chairman of the Defence Scientific Advisory Council. He was appointed a CBE in 1996. He is the recipient of the 2001 Distinguished Achievement Award of the Institute of Electrical and Electronics Engineers Antennas and Propagation Society, and in 2015 he received the Sir Frank Whittle Gold Medal from the Royal Academy of Engineering.

Electronically steered metasurface antenna

Mobile devices, climate science, and autonomous vehicles all require advanced microwave antennas for imaging, radar, and wireless communications. We propose a waveguide-fed metasurface antenna architecture that enables electronic beamsteering from a lightweight circuit board with varactor-tuned elements. Our approach uses a unique feed structure and layout that enables spatial sampling at the Nyquist limit of half a wavelength. We detail the design of this Nyquist metasurface antenna and experimentally demonstrate electronic beamsteering in two directions. Nyquist metasurface antennas can realize high performance without costly and power hungry phase shifters, making them a compelling technology for future antenna hardware.

Specific Resonant Properties of Non-Symmetrical Microwave Antennas

The aircraft avionics modernization process often requires optimization of the aircraft itself. Scale models of aircraft and their antennas are frequently used to solve this problem. Here we present interesting properties of the resonant antennas, which were discovered serendipitously during the measurement process of some microwave antennas’ models as part of an aircraft modernization project. Aircraft microwave antennas are often designed as non-symmetric flat microwave antennas. Due to their thin, low and longitudinally elongated outer profile, they are also called tail antennas. An analysis of the resonant properties of non-symmetric antennas was performed in the band from 1 GHz to 4 GHz. The length of the antenna models ranged from 2 cm to 7 cm. The width of the antennas, together with the thickness of the strip, was always a constant parameter for one measured set of six antennas. In the measurement and subsequent analysis, attention was focused on the first-series resonant frequency (λ/4) of each antenna. During the evaluation of the resonance parameters, the flat microwave antenna models showed specific resonant properties different from those of conventional cylindrical microwave antennas. This article aims to inform professionals about these unknown specific properties of non-symmetrical antennas. The results of experimental measurements are analyzed theoretically and then visually compared using graphs so that the reader can more easily understand the properties observed. These surprising observations open up some new possibilities for the design, implementation, and use of flat microwave antennas, as found in modern aircraft, automobiles, etc.

Derivation of Far-field Gain Using a Gain Reduction Effect in the Fresnel Region

A handy method of calculating far-field gain based on the magnitude of the power transmission in a Fresnel region is presented, which can be applied to the phaseless near-field measurement. Due to the short range inside an anechoic chamber, the probe antenna is often placed in the Fresnel region of the antenna under test (AUT). It is well-known that far-field gain of an antenna gradually reduces when one antenna moves to the other one placed in a proximity distance. This fact can be advantageously applied to estimate the far-field gain in a far-field region. The proposed method offers rapid estimation of the far-field gain based on the simple input knowledge such as the probe antenna gain and the magnitude of the power transmission and the separation distance between AUT and probe antenna. The proposed method can be applicable to a wide range of microwave antennas. This feature makes it possible to offer preliminary measurement results and reference parameters of the measurement for the various types of microwave antennas.

Modern devices, antennas and reflectors with nonreciprocal properties (review).

The review deals with microwave antennas, devices (including reflectors), materials and media with nonreciprocal properties, which, due to their uniqueness and promising application, have become the topic of a large number of scientific studies and publications. It is noted that amplitude nonreciprocity can be realized not only with the help of magnetized ferrites and semiconductor amplifiers, but also based on parametric and nonlinear structures using space-time modulation. Therefore, polarization nonreciprocity can also be achieved on magnet-free components, including varactors, and other parametric elements. When analyzing reciprocal reflectors made both on "thin" surface structures and on bulk waveguides, it is appropriate to consider reciprocal cross-polarizing (depolarizing) "invisible"-reflectors, converting the initial polarization of the incident wave into the orthogonal polarization of the reflected wave, which can be built with using only reciprocal passive components without the use of non-reciprocal ones (ferrite circulators, gyrators, etc.). The combination of polarization and nonreciprocal properties in radar reflectors, RFID tags, etc., is an additional degree of freedom in the design of new generation electronic systems.