Mohamed S. Kheir

Graphical Representation and Evaluation of Attenuation and Coupling Parameters of Whispering-Gallery-Mode Resonators

A new graphical approach for extracting the attenuation and coupling coefficients of traveling-wave whispering-gallery-mode (WGM) resonators is proposed. This approach starts by representing the transmission coefficient circle on the complex plane at the resonance frequency. From the metrics of this circle (center position and radius), both the attenuation and coupling coefficients can be extracted. This technique simplifies the evaluation of the loaded and unloaded Q factors of WGM resonators directly from the extracted coefficients. It is applied to a K-band planar WGM resonator coupled to a dielectric image guide in a reaction-mode configuration. The extracted values from both simulations and measurements show a close agreement with the mathematical model of traveling-wave WGM resonators.

BROADBAND MATERIAL CHARACTERIZATION USING TRAVELING-WAVE WHISPERING-GALLERY -MODE DIELECTRIC RESONATORS

A new technique for broadband material characterization, using a whispering-gallery-mode (WGM) resonator, is proposed. The resonant perturbation method is applied for the measurement of both the dielectric constant and loss tangent of various types of materials and over a wide frequency band. A comprehensive study on the reliability of using such technique, via simulations and measurements, is conducted as well. The feasibility of this device in sensing small variations of the dielectric properties of the material is investigated. Furthermore, the geometry of the resonator is slightly modifled to flt liquid materials as well. This can be a promising solution for sensing human-body tissues or liquids such as blood or urine due to the sensitive nature of these resonators. The experimental setup is successfully utilized to measure the dielectric constant of a water droplet as a liquid sample as well as difierent material samples of arbitrary shapes and dielectric properties. The measurements are performed over the whole X- and K-bands where the obtained results are with a maximum deviation of only 3.3% for solids and 4.5% for liquids.

Non-destructive broadband material characterization over the K-band using whispering-gallery-mode resonators

A precise technique for broadband material characterization, using a whispering-gallery-mode (WGM) resonator, is proposed. The resonant perturbation method is successfully applied for extracting both the dielectric constant and loss tangent of materials over a wide frequency band. Two experimental prototypes are fabricated and employed over the K-band where consistent results are obtained with a maximum error of ±3.3%.

Design and characterization of 77 GHz and 120 GHz Schottky diode mixers for antenna measurements

Some passive millimeter-wave harmonic mixers with integrated LO-IF diplexers have been designed and characterized for both 77 GHz and 120 GHz frequency bands. These modules have been employed to work as an extension for the higher millimeter-wave antenna measurements, particularly the radiation pattern. Through this article, several characterized parameters have been presented, such as the conversion loss, the IF and LO return loss and the LO-IF isolation, besides the design and simulation procedures of the integrated diplexer and the RF and LO impedance matching networks of the mixer. The realized modules have been used to record the radiation pattern of two antennas operating at the same band.

Broadband characterization of planar whispering-gallery-mode dielectric resonators using a simple experimental setup

A simple and cost-effective experimental setup for measuring the transmission coefficient of whispering-gallery (WG) mode dielectric resonators up to the mm-wave band is presented. The proposed setup consists of a sweep generator, a spectrum analyzer and a PC with a General Purpose Interface Bus (GPIB). The major advantage of such arrangement lies in the ease of measurement without standard calibration procedures as well as its cost-effectiveness. Using this setup, two WG resonators have been experimentally characterized over the K- and Ka-bands. The obtained results are in a good agreement with those obtained from a calibrated vector network analyzer.

Experimental investigation of whispering-gallery-mode dielectric resonators for biological material characterization

A whispering-gallery-mode (WGM) dielectric resonator is proposed as a biological material sensor. This paper investigates the feasibility of this device in sensing small variations within the dielectric properties of the material regardless its shape, volume or position. The geometry of the resonator is slightly modified to fit liquid materials testing. This solution can be promising for sensing human-body tissues or liquids such as blood or urine. The experimental setup is successfully utilized to detect the dielectric constant of a water droplet as a liquid sample and another bulky material of an arbitrary shape. The material measurements are performed over the X-band where accurate results are obtained.

Broadband directional couplers using traveling-wave whispering-gallery-mode dielectric resonators

This paper presents a broadband directional coupler using traveling-wave (TW) whispering-gallery-mode (WGM) resonators. The proposed directional coupler consists of two microstrip lines and two thin dielectric disks. The coupling ratio can be controlled by adjusting the spacing between both resonators and transmission lines.

A novel mode-identification technique for material characterization using whispering-gallery-mode resonators

A novel mode-identification approach for permittivity measurement using traveling-wave (TW) whispering-gallery-mode (WGM) resonators is proposed. This approach is based on extracting the attenuation and coupling coefficients of the resonator directly from the measured complex insertion loss values. From both coefficients, the modal index of the resonance frequency will be easily identified. This approach is applied to an implemented K-band dielectric resonator where excellent results are obtained

Evaluation of the loaded and unloaded q-factors of traveling-wave whispering-gallery-mode resonators

A new graphical approach for evaluating the loaded and unloaded Q-factors of traveling-wave (TW) whispering-gallery-mode (WGM) resonators is proposed. This approach is based on extracting the attenuation and coupling coefficients of the resonator directly from the measured complex insertion loss values. The extracted Q-factor values of a measured K-band resonator are verified by using the well-known reaction method where rigorous results are obtained.

An Extremely Compact UWB Microstrip Annular Ring Filter for Bluetooth Applications

This paper presents a novel microstrip ring filter with a center frequency (f0) of 2.4 GHz and ultra-wideband (UWB) characteristics. It has an extremely compact size (10mm times 10mm). A Fractional Bandwidth (FBW) of around 120% and a sharp rejection greater than 40 dB have been achieved. Two transmission zeros have been introduced by adding short-circuit vias at the band edges which provide a reasonably good insertion loss. The experimental results show a good agreement with simulations. This filter can be utilized for Bluetooth applications due to its miniature size, wide bandwidth, and enhanced out-of-band rejection