An experimental investigation of the radiation and circuit properties of a resonant cylindrical dielectric cavity antenna has been undertaken. The radiation patterns and input impedance have been measured for structures of various geometrical aspect ratios, dielectric constants, and sizes of coaxial feed probes. A simple theory utilizing the magnetic wall boundary condition is shown to correlate well with measured results for radiation patterns and resonant frequencies.

The resonant cylindrical dielectric cavity antenna

Sensing technology has been widely investigated and utilized for gas detection. Due to the different applicability and inherent limitations of different gas sensing technologies, researchers have been working on different scenarios with enhanced gas sensor calibration. This paper reviews the descriptions, evaluation, comparison and recent developments in existing gas sensing technologies. A classification of sensing technologies is given, based on the variation of electrical and other properties. Detailed introduction to sensing methods based on electrical variation is discussed through further classification according to sensing materials, including metal oxide semiconductors, polymers, carbon nanotubes, and moisture absorbing materials. Methods based on other kinds of variations such as optical, calorimetric, acoustic and gas-chromatographic, are presented in a general way. Several suggestions related to future development are also discussed. Furthermore, this paper focuses on sensitivity and selectivity for performance indicators to compare different sensing technologies, analyzes the factors that influence these two indicators, and lists several corresponding improved approaches.

A Survey on Gas Sensing Technology

Microwave passive and active devices containing dielectric resonators and the design procedures used to characterize these components are reviewed. The emphasis has been on low noise, small size, low cost and high temperature stability. Both filter and oscillator applications are described. The applications of dielectric resonators in the millimeter-wave frequency band are also discussed. >

http://ieeexplore.ieee.org/iel2/741/1062/00027611.pdf

Dielectric resonators

In addition to the constant demand of low-loss dielectric materials for wireless telecommunication, the recent progress in the Internet of Things (IoT), the Tactile Internet (fifth generation wireless systems), the Industrial Internet, satellite broadcasting and intelligent transport systems (ITS) has put more pressure on their development with modern component fabrication techniques Oxide ceramics are critical for these applications, and a full understanding of their crystal chemistry is fundamental for future development Properties of microwave ceramics depend on several parameters including their composition, the purity of starting materials, processing conditions and their ultimate densification/porosity In this review the data for all reported low-loss microwave dielectric ceramic materials are collected and tabulated The table of these materials gives the relative permittivity, quality factor, temperature variation of the resonant frequency, crystal structure, sintering temperature, measurement 

Low-loss dielectric ceramic materials and their properties

This review is focused on the latest developments in continuous-wave (CW) photomixing for Terahertz (THz) generation. The first part of the paper explains the limiting factors for operation at high frequencies ∼ 1 THz, namely transit time or lifetime roll-off, antenna (R)-device (C) RC roll-off, current screening and blocking, and heat dissipation. We will present various realizations of both photoconductive and p-i-n diode–based photomixers to overcome these limitations, including perspectives on novel materials for high-power photomixers operating at telecom wavelengths (1550 nm). In addition to the classical approach of feeding current originating from a small semiconductor photomixer device to an antenna (antenna-based emitter, AE), an antennaless approach in which the active area itself radiates (large area emitter, LAE) is discussed in detail. Although we focus on CW photomixing, we briefly discuss recent results for LAEs under pulsed conditions. Record power levels of 1.5 mW average power and conversion efficiencies as high as 2 × 10−3 have been reached, about 2 orders of magnitude higher than those obtained with CW antenna-based emitters. The second part of the paper is devoted to applications for CW photomixers. We begin with a discussion of the development of novel THz optics. Special attention is paid to experiments exploiting the long coherence length of CW photomixers for coherent emission and detection of THz arrays. The long coherence length comes with an unprecedented narrow linewidth. This is of particular interest for spectroscopic applications, the field in which THz research has perhaps the highest impact. We point out that CW spectroscopy systems may potentially be more compact, cheaper, and more accurate than conventional pulsed systems. These features are attributed to telecom-wavelength compatibility, to excellent frequency resolution, and to their huge spectral density. The paper concludes with prototype experiments of THz wireless LAN applications. For future telecommunication systems, the limited bandwidth of photodiodes is inadequate for further upshifting carrier frequencies. This, however, will soon be required for increased data throughput. The implementation of telecom-wavelength compatible photomixing diodes for down-conversion of an optical carrier signal to a (sub-)THz RF signal will be required.

/pdf/tunable-continuous-wave-terahertz-photomixer-sources-and-rulvqaamg0.pdf

Tunable, continuous-wave Terahertz photomixer sources and applications

This paper describes the development of microwave filter technology from an applications perspective. Military applications required wide-band and tunable devices for electronic support measures receivers, which led to the development of highly selective wide-band waveguide filters, coaxial resonator and suspended-substrate multiplexers, and electronically tunable filters. The satellite communications industry created demand for low-mass narrow-band low-loss filters with severe specifications on amplitude selectivity and phase linearity. These requirements resulted in the development of dual-mode waveguide and dielectric-resonator filters, and advances in the design of contiguous multiplexers. Cellular communications base-stations demanded low-loss high power-handling selective filters with small physical size, capable of being manufactured in tens of thousands at a reasonable cost. These demands led to advances in coaxial resonator, dielectric resonator, and superconducting filters, and also to methods of cost-reduction, including computer-aided alignment. Cellular radio handsets have required the manufacture of hundreds of millions of extremely small very low-cost filters, still with reasonably low loss and high selectivity. This has driven significant advances in integrated ceramic, surface, and bulk acoustic-wave active filters and filters using micromachined electromechanical systems.

Microwave filters-applications and technology

The utilization of planar millimeter-wavelength whispering gallery dielectric resonator modes for the design of W-band directional filters and power combiners is studied. The device presented combines the output power of several millimeter-wavelength devices in a single step by means of whispering gallery dielectric resonator (DR) modes. At millimeter wavelengths the cylindrical DRs used on their conventional TE, TM, or hybrid modes are impractically small. When used in their whispering gallery modes (WGMs) these cylindrical DRs have dimensions larger than normal for millimeter wavelength. After a description of the WGM phenomena, both electromagnetic and circuit parameters of these resonators are defined when they are coupled with transmission lines. The analysis based on the ring resonator model makes it possible to predict the theoretical responses of any devices. Experimental results obtained for directional filters and for power combiners in W-band are given. >

Whispering gallery dielectric resonator modes for W-band devices

The Rayleigh-Ritz method and the finite element method nongenerating spurious solutions are employed for analysis of whispering gallery modes (WGMs) in cylindrical single-crystal anisotropic dielectric resonators. These methods allow accurate computation of the resonant frequencies, the Q-factors (depending on the dielectric and on the conductor losses), and the electromagnetic field distributions for all WGMs in the presence of additional elements like metal shields, MIC substrate, or supports. Different families of modes are studied both theoretically and experimentally. The mode coupling phenomenon is investigated. A WGM single-crystal quartz resonator is presented having an unloaded Q-factor greater than 30000 at about 100 GHz, including radiation and dielectric losses. >

Study of whispering gallery modes in anisotropic single-crystal dielectric resonators

The applications of dielectric resonators are currently of considerable interest in microwave integrated circuits. The design of a dielectric resonator depends on its natural resonant frequencies. Since exact solutions of dielectric rectangular and cylindrical resonators cannot be rigorously computed a new and more accurate method has been developed to solve this problem. In this method all the surfaces are simultaneously considered as imperfect magnetic walls. Theoretical values agree very well with experimental results. The difference being less than 1 percent.

Accurate Resonant Frequencies of Dielectric Resonators

The purpose of this paper is to show the feasibility of millimeter-wave resonators utilizing whispering-gallery (WG) modes excited in planar and cylindrical dielectric structures. Measured resonant frequencies and quality factors in Ka- and W-bands are reported. Their applications to millimeter-wave integrated circuits are also dealt with. For this, a bandstop filter obtained by coupling two WG-mode dielectric resonators to a dielectric image guide is presented at about 35 GHz.

P. Guillon

Papers

Microwave filters-applications and technology

Whispering gallery dielectric resonator modes for W-band devices

Study of whispering gallery modes in anisotropic single-crystal dielectric resonators

Accurate Resonant Frequencies of Dielectric Resonators

Whispering-Gallery Modes of Dielectric Structures: Applications to Millimeter-Wave Bandstop Filters