Electric and Magnetic One- And Two-Dimensionally Tuned Parameter-Agile Substrate Integrated Waveguide Components and Devices

Les composants micro-ondes et millimétriques accordables constituent des éléments importants rencontrés dans les systèmes de radiocommunications et radars. En effet, ils donnent la possibilité à ces derniers d'être adaptables et ajustables. Or, ces deux caractéristiques sont importantes puisqu'elles permettent aux systèmes de s'adapter à des changements de leurs spécifications sans avoir à changer leurs circuits. Il peut y avoir en effet plusieurs raisons qui amèneraient à procéder à des modifications de spécifications d'un système : des variations des conditions environnementales (liées à la température, l'humidité, ou encore aux vibrations), et des changements liés à des contraintes de nouveaux clients comme par exemple l'utilisation de nouvelles bandes de fréquence ou de canaux. Il serait vraiment peu efficace d'avoir à reconcevoir l'ensemble du système afin de satisfaire de nouvelles performances. Ainsi, il est important de concevoir le système de façon à ce qu'il puisse s'ajuster ou se corriger pour toutes modifications qui pourraient arriver. Par exemple, si la réponse fréquentielle d'un filtre passe-bas commence à glisser vers des fréquences plus basses avec une augmentation de la température, le système le mettant en oeuvre pourrait ne plus être en mesure de recevoir ou transmettre de l'information dans cette bande de fréquence. Cependant, si le même filtre peut être ajusté en fréquence, il sera alors possible de le corriger et de le refaire fonctionner dans ses spécifications d'origine. Dans la littérature, on trouve de nombreuses méthodes qui permettent de concevoir des éléments et composants ajustables aux fréquences micro-ondes. Les méthodes employées les plus populaires mettent en oeuvre : des composants semi-conducteurs (tels que des diodes varicaps, des diodes PIN et des transistors), des microsystèmes électromécaniques (ou MEMS pour microelectro- mechanical systems), des matériaux ferroélectriques et des matériaux ferromagnétiques. Dans certaines de ces conceptions, des combinaisons de ces différentes méthodes ont également été adoptées afin d'obtenir de meilleures performances. Ce travail présente de nouveaux types de composants micro-ondes ajustables basés sur les Guides d'onde Intégrés au Substrat (GIS). La technologie GIS peut être considérée comme une forme planaire de la technologie guide d'onde conventionnelle, dont elle hérite de la plupart des propriétés. Par exemple, comme pour les guides d'onde conventionnels, les guides GIS sont faibles pertes et peuvent être mis en oeuvre pour de fortes puissances. Bien que le GIS soit similaire au guide d'onde sur de nombreux aspects, il présente une taille et un coût plus réduit.

Abstract

Microwave and millimeter wave tunable devices, circuits and components are one of the most important parts in any communication and radar system design. The tunable devices, circuits and components which are integrated into a system enable it to become more adaptive and flexible in nature. The adaptive and flexible system can be reconfigured to follow the changes that occur into its variable or adjustable specifications without changing its hardware design. There may be several reasons that could lead to the change in the system specifications: changes in the environmental conditions (related to temperature, humidity, and vibration), and changes due to new customer requirements, for example, the inclusion of a new operating frequency band or channel. It would be very impractical to re-design all the system components just to meet the new performance criteria. Hence, it is important to design the system in a way that it can adjust or correct itself for any changes that might occur. For example, if a band-pass filter frequency response begins to drift towards a lower frequency value with the increase in temperature, it might not be able to receive or transmit valuable information at this frequency band. However, if the same band pass filter can be made frequency tunable, it will be able to get self-corrected and bring its frequency response back to the original value. In literature, there are many methods that are used in realizing tunable microwave circuits and components. The most popular methods in the realization of tunable components make use of semiconductor elements and devices (including varactor diodes, PIN diodes, and transistors), micro-electro-mechanical systems (MEMS) switches and capacitors, ferroelectric materials, and ferromagnetic materials. In some of the designs to achieve a better tuning performance, even combinations of two different tuning methods have also been adopted. In this work, new types of microwave tunable devices, circuits and components based on substrate integrated waveguide (SIW) are presented. SIW technology can be considered as a synthesized planar form of rectangular waveguide, and inherits almost all of its properties. For example, similar to rectangular waveguide, SIW is lower in loss, it can be used for higher power applications compared to conventional planar counterparts, and it is lower in cost. Although SIW is similar to rectangular waveguide in many aspects, it holds a significant difference in terms of size. Rectangular waveguide is usually made of hollow metallic tube (rectangular or circular), therefore at a given frequency, its size is much larger than the conventional planar transmission lines (microstrip or coplanar). Thus, even though rectangular waveguide being capable of delivering outstanding RF performance cannot be directly used in realizing compact planar circuits. Since SIW technology inherits almost all the properties of rectangular waveguide and also it is planar in nature, it is an outstanding candidate in realizing microwave and millimeter wave planar integrated circuits. However, SIW is usually fabricated on dielectric substrate, thus its power handling capabilities and its performance in terms of losses are largely dependent upon substrate material used and structure topology. In this work, SIW-based microwave tunable devices, circuits and components using ferromagnetic materials are presented. Ferrites or ferromagnetic material permeability value can be controlled through the application of an external DC magnetic bias. Since the propagation constant of an RF signal is directly proportional to the square root of the material permittivity and permeability. Therefore, any change in the permeability component also changes the propagation constant of the electromagnetic wave. Thus, using ferrite materials allow the realization of very interesting reconfigurable devices. Another important characteristic of ferrite materials is that they display non-reciprocal behaviour. This means that RF signals, propagating in two different directions in the ferrite material can have different characteristic behaviours. This is a very interesting feature, which can be used not only to realize tunable microwave devices, but also devices that are non-reciprocal in nature. Some of the ferrite-based non-reciprocal devices include isolator, gyrator, and circulator. In literature, it can be observed that most of the nonreciprocal and tunable devices using ferrite materials are designed based on rectangular waveguide technology. The low loss and high power handling property of rectangular waveguide make them an attractive candidate in realizing ferrite based tunable devices. Moreover, for a rectangular waveguide operating with dominant TE10 mode, the maximum magnitude of its electric field occurs at the central region, whereas the maximum magnitude of its magnetic field occurs along the sidewalls. This distribution of electric and magnetic fields, allows placing the ferrite materials in the regions of the highest magnetic field without perturbing the electric field distribution. Since the ferrite materials interact strongly with magnetic field, they are usually placed in the regions where the magnetic field concentration is highest. Although rectangular waveguide is a very promising technology in realizing high power magnetically tunable devices, they cannot be readily integrated in a planar form.