Conical and biconical ultra-high-Q optical-fiber nanowire microcoil resonator

New 3D geometries of the optical nanowire microcoil resonator are suggested and investigated theoretically. The dependence of the Q factor on coupling parameters is calculated and compared for three different profiles. Results suggest that ultra-high-Q resonators can be fabricated more easily when the nanowire microcoil resonator has a biconical profile.     

Wideband stair-shaped dielectric resonator antennas

Wideband stair-shaped dielectric resonator antenna (DRAs) are designed. Wide bandwidths are achieved with one-step or two-steps stair geometries. Cricular and square cross-sections are discussed with two different excitation methods: coaxial feed and aperture coupled. The DRAs are designed in the X-band. An impedance bandwidth (S₁₁<-10 dB) of 54.3% is obtained with the two-steps stair-shaped DRA. The antennas have broadside radiation patterns in all cases across the matching band. In addition, embedding the base into another dielectric material reduces the size of the stair-shaped DRA. Simulation results are compared with measurements and reasonable agreement is obtained     

Losses of the parallel-plate dielectric resonator

The various loss aspects of the parallel-plate microwave dielectric resonator for the TE_01delta mode is studied from a modified field model. The main merit of this field model is that it provides very simple electromagnetic field expressions of this field mode. Various methods of calculation of losses are discussed. The analyses of the calculated results of conductor and radiation losses are given. The relationship of the loss with the dimensions of the device is introduced. By conducting practical measurements to compare with theoretical calculation results, this modified model has shown dramatic improvement over the unmodified model. The dielectric loss measurement by using this parallel-plate dielectric resonator is also studied.     

Low profile wideband embedded dielectric resonator

A dielectric resonator antenna (DRA) made of high dielectric constant substrate is studied. Embedding a higher dielectric disk inside the substrate disk enhances the bandwidth. A narrow slot excites the DRA. Embedded DRAs of different shapes are considered for wideband applications. An eye-shaped DRA made with a circular dielectric resonator disk embedded in an elliptical-shaped `host' DRA is found to have an impedance bandwidth of 28% with stable broadside patterns     

Excitation of ray oscillations in quasioptical dielectric cavities with whispering gallery modes

It is observed that ray oscillations may be excited together with whispering gallery modes in quasioptical dielectric cavities. It is shown that as the excitation conditions change, the fields of these oscillations gradually “split off” from the fields of the whispering gallery modes whose characteristics deteriorate. The angular spectrum of ray oscillations in dielectric cavities is determined. Pis’ma Zh. Tekh. Fiz. 23, 25–29 (August 12, 1997)     

Compact wideband multi-layer cylindrical dielectric resonator antennas

Homogenous dielectric resonator antennas (DRAs) have been studied widely and their bandwidth have been reached to the possible upper limit. A new non-homogenous DRA, multilayer cylindrical DRA (MCDRA), is designed and fabricated to achieve wider bandwidth. The antennas consist of three different dielectric discs, one on top of the other. Two different excitation mechanisms are studied here. As much as 66% of impedance bandwidth with a broadside radiation pattern has been demonstrated using a 50 Omega coaxial probe placed off the antenna axis. More than 32% of impedance with a broadside radiation pattern has been achieved when the antenna is excited by an aperture coupled 50 Omega microstrip feedline. Mode analysis is carried out to investigate the natural resonance behaviours of the MCDRA structure.     

Analysis of whispering-gallery superconducting dielectric resonator modes

The whispering-gallery (WG) modes of a superconducting dielectric resonator (SDR) based on a sapphire cylindrical dielectric resonator and a YBa₂Cu₃O_{7 –} shielding cylinder have been studied. A method for the determination of the resonant frequencies and the maximum quality factor of such modes is presented. Calculations have shown that most of the mode energy could be confined between the caustic surface of the WG modes provided the dimensions of the SDR are properly selected, and a magnitude of 10⁹ forQ of the SDR could be estimated. A phenomenal explanation is given to account for such outstanding microwave behavior.     

Auto-oscillatory system based on dielectric resonator with whispering-gallery modes

A new method of microwave generation in a system with high-Q quasi-optical cylindrical dielectric resonator (CDR) excited by an azimuthal-periodic electron beam current is proposed. Characteristic parameters of a cylindrical fluoroplastic CDR have been determined. Data on microwave generation in a system based on a CDR with whispering-gallery eigenmodes excited by a relativistic azimuthal-periodic electron beam current are presented. Electromagnetic radiation of this system was measured using a detector for the 8-mm wavelength range.     

Optimal electrical thickness of dielectric samples in resonator measurements

Translated from Izmeritel'naya Tekhnika, No. 8, pp. 37–39, August, 1988.     

Compact dielectric resonator antenna for microwave breast cancer detection

A compact stair-shaped dielectric resonator antenna (DRA) is designed and fabricated for microwave breast cancer detection. A quarter-wavelength choke was incorporated to reduce the finite ground plane size. A more than 40% return loss of 10 dB centred at 6.5 GHz is achieved with a 50 Ω coaxial port. Parametric studies are carried out to provide practical insights into sensor design. The design is performed numerically and confirmed experimentally. A simple model for the tissue is considered and the interaction of the sensor with the tissue is investigated. Good matching is retained without adding any matching medium or lumped loads when the sensor is in contact with the tissue. A two-element sensor array is investigated numerically. A dipole antenna and a circular ultra-wideband dipole antenna are compared with the stair-shaped DRA with a choked ground plane. Preliminary results are obtained for the cases with different tumour locations. The DRA type of sensor reveals good potential for frequency-domain detection.     

The influence of finite end screens on the spectrum of oscillations in cylindrical quasioptical dielectric resonators

We have studied the influence of finite dimensions of the end screens on the spectrum of whispering gallery modes in a teflon cylindrical quasioptical resonator. The dependence of the resonance oscillation frequency on the radius of conducting end screens is determined for the first time. Variation of the screen radius leads to transformation of the axial index of HE modes.     

Complex permittivity measurements of ferroelectrics employing composite dielectric resonator technique

Composite cylindrical TE(0n1) mode dielectric resonator has been used for the complex permittivity measurements of ferroelectrics at frequency about 8.8 GHz. Rigorous equations have been derived that allowed us to find a relationship between measured resonance frequency and Q-factor and the complex permittivity. It has been shown that the choice of appropriate diameter of a sample together with rigorous complex angular frequency analysis allows precise measurements of various ferroelectric. Proposed technique can be used for materials having both real and imaginary part of permittivity as large as a few thousand. Variable temperature measurements were performed on a PbMg(1/3)Nb(2/3)O3 (PMN) ceramic sample, and the measured complex permittivity have shown good agreement with the results of measurements obtained on the same sample at lower frequencies (0.1-1.8 GHz).     

Improvement of open resonator technique for dielectric measurement at millimetre wavelengths

An open resonator system is designed and constructed for the accurate measurement of complex permittivity at Ka band. It is solved successfully for the first time in how to achieve the consistency of cavity lengths corresponding to different resonant frequencies over a broad band and how to determine the proper permittivity from multiple transcendental equation roots of one sample. Many kinds of samples such as fused quartz, Teflon, quartz ceramic, MgF₂ and MgAl₂O₄ are measured and the results are in good agreement with published data. The systematic error analysis shows that the relative standard deviation of the measurement system is less than 0.172% for permittivity and 18.35% for loss tangent. The software developed to control the system improves the measurement efficiency greatly.     

Whispering gallery modes induced in a partly shielded hemispherical dielectric resonator

Whispering gallery modes induced in a partly shielded hemispherical dielectric resonator by lumped radiation sources were experimentally studied for the symmetric and asymmetric arrangement of the hemisphere relative to the cylindrical metal shield. The oscillation mode characteristics are presented for the shielded hemispherical resonator and an analogous open dielectric resonator. The proposed resonator is a promising device for the creation of highly stable solid-state millimetric wave oscillators.     

An X-band, high power dielectric resonator oscillator for future military systems

A 9.0-GHz dielectric resonator oscillator (DRO), generating a CW output power of 2.5 W at room temperature, has been designed and fabricated using a high-power GaAs MESFET and a dielectric resonator (DR) in a parallel feedback configuration. The oscillator exhibited a frequency stability of better than 130 ppm, without any temperature compensation, over the range -50 degrees C to +50 degrees C. The output power varied from +35 dBm (3.2 W) at -50 degrees C to +33 dBm (2 W) at +50 degrees C. The single-sideband phase noise levels were measured and found to be -105 and -135 dBc/Hz, at 10- and 100-kHz carrier offset frequencies, respectively. The oscillator output was then fed into a single-stage high-power MESFET amplifier, resulting in a total RF power output of 6.5 W. The overall DC to RF conversion efficiency of the 6.5-W unit was approximately 15.3%     

Numerical investigation on compact multimode dielectric resonator antennas of very high permittivity

An electrically small antenna based on a dielectric resonator antenna (DRA) is investigated. Two wellknown simulation techniques, the finite element method and the finite integration technique have been applied to study a low volume high permittivity DRA. It is demonstrated that the design of a compact size and wide frequency coverage DRA for 2.4?2.5 GHz ISM frequency band is possible by proper selection of the resonator shape in combination with appropriate resonant modes. Numerical results for one particular antenna design are reported.     

The open resonator with a longitudinally placed dielectric film in measurement technique

The case when a thin dielectric film is placed longitudinally in an open resonator is considered. When measuring the parameters of the film this arrangement enables one to increase the volume of material introduced into the field without any appreciable distortion of the field of the open resonator and also increases the deviations of the measured parameters.Translated from Izmeritel'naya Tekhnika, No. 10, pp. 50–51, October, 1993.We wish to thank V. N. Apletalin for his help with the experiment.