There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Over the past three decades a new spectroscopic technique with unique possibilities has emerged. Based on coherent and time-resolved detection of the electric field of ultrashort radiation bursts in the far-infrared, this technique has become known as terahertz time-domain spectroscopy (THz-TDS). In this review article the authors describe the technique in its various implementations for static and time-resolved spectroscopy, and illustrate the performance of the technique with recent examples from solid-state physics and physical chemistry as well as aqueous chemistry. Examples from other fields of research, where THz spectroscopic techniques have proven to be useful research tools, and the potential for industrial applications of THz spectroscopic and imaging techniques are discussed.

Terahertz spectroscopy and imaging – Modern techniques and applications

The substrate integrated waveguide (SIW) technique makes it possible that a complete circuit including planar circuitry, transitions, and rectangular waveguides are fabricated in planar form using a standard printed circuit board or other planar processing techniques. In this paper, guided wave and modes characteristics of such an SIW periodic structure are studied in detail for the first time. A numerical multimode calibration procedure is proposed and developed with a commercial software package on the basis of a full-wave finite-element method for the accurate extraction of complex propagation constants of the SIW structure. Two different lengths of the SIW are numerically simulated under multimode excitation. By means of our proposed technique, the complex propagation constant of each SIW mode can accurately be extracted and the electromagnetic bandstop phenomena of periodic structures are also investigated. Experiments are made to validate our proposed technique. Simple design rules are provided and discussed.

Guided-wave and leakage characteristics of substrate integrated waveguide

Substrate-integrated waveguide (SIW) technology represents an emerging and very promising candidate for the development of circuits and components operating in the microwave and millimetre-wave region. SIW structures are generally fabricated by using two rows of conducting cylinders or slots embedded in a dielectric substrate that connects two parallel metal plates, and permit the implementation of classical rectangular waveguide components in planar form, along with printed circuitry, active devices and antennas. This study aims to provide an overview of the recent advances in the modelling, design and technological implementation of SIW structures and components.

Review of substrate-integrated waveguide circuits and antennas

The integrated planar technique has been considered as a reliable candidate for low-cost mass production of millimeter-wave circuits and systems. This paper presents new concepts that allow for a complete integration of planar circuits and waveguide filters synthesized on a single substrate by means of metallized post (or via-hole) arrays. Analysis of the synthesized integrated waveguide and design criteria are presented for the post pitch and diameter. A filter design method derived from a synthesis technique using inductive post is presented. An experimental three-pole Chebyshev filter having 1-dB insertion loss and return loss better than 17 dB is demonstrated. Integrating such planar and nonplanar circuits on a substrate can significantly reduce size, weight, and cost, and greatly enhance manufacturing repeatability and reliability.

Single-substrate integration technique of planar circuits and waveguide filters

This paper analyses the beam squint compensation of the Sardinia Radio Telescope, when used for deep-space Telemetry, Tracking & Command. The proposed technique consists in the displacement of the lower beam-waveguide mirrors to separate the transmission and reception beams of the antenna. Two design approaches are discussed. The first is a bottom-up method, very accurate and straightforward but requiring many repeated and time-consuming analyses of the whole antenna. The second method is a top-down approach, based on the electromagnetic field matching on a fictitious planar grid defined along the beam-waveguide. This second method is much faster and it allows for implementing an automatic routine, based on an analytical formulation, to determine the best mirror movement for a given beam squint.

http://ieeexplore.ieee.org/iel5/6423128/6459071/06459145.pdf

Beam squint compensation technique for the Sardinia Radio Telescope

This paper presents a novel physical-based approach for the broadband modeling of printed periodic structures. This approach is based on the use of the MoM/BI-RME method: this method is an efficient integral-equation technique that adopts entire-domain basis functions. By exploiting the physical nature of these basis functions (which are related with the modes of a 2D resonator), an RLC equivalent circuit model is derived, which accurately describes the frequency response over a very broad frequency band. Validation examples are reported in the case of frequency selective surfaces, both for normal and oblique incidence, showing the rapidity of the approach, as well as its accuracy in representing both the co-polar and cross-polar transmission/reflection coefficients.

Physical-based broadband modeling of printed periodic structures by the MoM/BI-RME method

Autotrack systems for space applications are typically based on monopulse. These systems require a specific test before being operative, typically through calibration towers, leading to expensive operating costs and antenna downtime. This work aims to present a technique to test in-lab these systems by the generation of high order modes as if they would be coupled using a calibration tower as well-known target. The theoretical working principle and a proof-of-concept design will be presented in Ku-band to confirm the reliability of the model.

In-Lab Calibration of Single TE21 Monopulse Tracking Systems

This paper presents a review of the major applications of substrate integrated waveguide (SIW) cavities and of the various techniques proposed in the last years to engineer the resonant cavities in SIW technology The aim of engineering the SIW cavities is multifold, and includes the size reduction, the loss minimization, and the optimization of the resonant modes pattern A variety of topologies of modified SIW cavity resonators are presented, together with their advantages and disadvantages, and several applications are described and discussed

Engineering the Resonant Cavities in Substrate Integrated Waveguide Technology

The full-wave analysis of arbitrarily shaped waveguide junctions allows to realize compact and low-loss new structures The practical realization of these waveguide elements, however, suffers from technological and mechanical constraints, whose effect is to change in a random way their frequency behaviour We propose a fast tolerance analysis, based on the BI-RME method, able to evidence the parts of the junction with higher sensitivity and to give the maximum permitted tolerances in the junction construction This tool can help the designers in the choice of the best suited manufacturing technology and therefore in the analysis of the production costs

Luca Perregrini

Papers

Beam squint compensation technique for the Sardinia Radio Telescope

Physical-based broadband modeling of printed periodic structures by the MoM/BI-RME method

In-Lab Calibration of Single TE21 Monopulse Tracking Systems

Engineering the Resonant Cavities in Substrate Integrated Waveguide Technology

H-plane waveguide junction design with mechanical and technological constraints