Single and multi-band signal-interference microwave filters with single-ended/balanced and reflectionless operational capabilities

Abstract

Microwave filters are essential radiofrequency (RF) components in advanced wireless systems for secure communications and defense applications, such as radar. However, the performance requirements for these RF circuits are becoming more stringent in terms of f iltering selectivity and other electrical properties so as to ensure a more robust operation of the full RF system against undesired electromagnetic (EM) interference and out-of-band noise. The primary purpose of these RF devices is to allow certain RF-signal frequency components to be transmitted within a specified spectral range (i.e., transmission band) while efficiently rejecting other spectral components outside this frequency region (i.e., attenuated band). On the other hand, as the information and communication technologies continue their rapid evolution and RF wireless applications become increasingly prevalent, there is a growing trend toward the development of intelligent wireless electronic systems featuring low profile, minimal latency, and low DC-power/energy consumption. This demand applies to both military and commercial scenarios, for which highlysophisticated multi-purpose RF transceivers and intelligent devices must be conceived. This is especially highlighted by recent advances in beyond-5G networks, Internet-of-Things (IoT), and artificial intelligence (AI), which require deep integration of diverse services and standards in the same RF platform. Such trend also affects to RF components as microwave bandpass filters (BPFs) as the RF-signal preselectors, in which multi-band and reflectionless operation is highly desired to acquire various RF signals at the same time with low impact over co-located RF actives stages in the full RF frontend chain. RF balanced or differential filters are also gaining significan attention, since they allow higher immunity to common-mode(CM) noise, crosstalk, and EM interference. The primary objective of this Ph. D. thesis is to develop advanced RF single- and multiband BPF devices based on signal-interference techniques that may offer additional capabilities; e.g., low out-of-band RF-power reflection, high CM rejection in balanced/differential planar implementations and multi-layer designs, or flat-group-delay/low-phasedistortion characteristics for digital communications. Thus, fully-new classes of RF f iltering components with advanced features are conceived in this Ph. D. thesis, including their theoretical analysis, design methodologies, and experimental verifications by means of several proof-of-concept prototypes. These demonstrative circuits have been realized in planar and 3-D technologies, namely microstrip for below-10-GHz designs, Groove Gap Waveguide (GGW) for the Ku-band, and conventional waveguide for the V-band. In this manner, the high versatility of the different types of engineered RF filtering components for distinct RF technologies and frequency regions is fairly confirmed. Specifically, a total of 22 prototypes for the aforementioned planar and 3-D technologies have been theoretically analyzed, designed, manufactured, and characterized in the development of this Ph. D. thesis.