Temperature dependence of composite microwave cavities

Composite microwave resonant cavities contain several regions of different dielectric materials. The variation of the resonant frequency with temperature is described in terms of a linear model. One part of the frequency variation is caused by the physical expansion of material parts, and the other by the change in the relative dielectric constant. The frequency sensitivity coefficients for both types of variation are obtained with the use of a computer code for numerical analysis of the electromagnetic field inside bodies of revolution     

Measurement of external Q factor of microwave oscillators using frequency pulling or frequency locking

Conditions are identified for the measurement of the external Q factor of microwave oscillators by use of frequency pulling or locking techniques. A small modification to a technique proposed previously for frequency locking is derived, and is extended to the case of frequency pulling. It is shown that measurements of the full locking or pulling bandwidths give information on the first derivatives, with respect to r.f.-voltage amplitude, of the device susceptance and conductance.     

A procedure for measuring the Q factor of and attenuation in microwave composite acoustic resonators

A procedure for measuring the Q factor of a microwave composite acoustic resonator is described. The resonator consists of a relatively thick crystal plate and a piezoelectric film with electrodes that is deposited on the plate. The procedure is based on mathematical processing of the array of measurement data on the coefficient of the electromagnetic-wave reflection from the resonator structure connected to a microwave reflectometer. Via this procedure, it is possible to obtain data on the Q factor at the resonance and antiresonance frequencies.     

Resonant scattering for characterization of axisymmetric dielectric objects

Resonances in the electromagnetic scattering by dielectric objects are investigated both numerically and experimentally with particular emphasis on their direct application to object characterization. Low ka calculations for spheres and an infinite circular cylinder illustrate the modal nature of the resonances and the dependence of the resonance spectra on refractive index and size. Experiments show that the specific wavelengths at which resonances occur in the scattering intensity from a glass fiber can be used to determine its diameter to a high accuracy. The extended boundary condition method is used to calculate the low ka resonances of a prolate spheroid and a finite circulate cylinder with the anticipation that the scattering resonances may be particularly suitable for characterizing randomly oriented nonspherical objects.     

Resonant Frequency and Q of an Open-Ended Rectangular Cavity

A field analysis of the TE /sub 10m/ resonant mode in an open-ended rectangular cavity is presented. The cavity geometry consists of rectangular waveguide with thick H-plane bifurcations for the terminations at each end. The bifurcation problem is solved by the method of modal analysis and a resonance criterion is established. Expressions for the cavity fields are written and used to compute stored energy, power lost, and Q. Calculated values for resonant frequency and Q are given and compared with experimental data.     

Theory and Measurement of Q in Resonant Ring Circuits

The loaded and unloaded Q of a resonant ring circuit are derived on the basis of the fundamental definition. Simple experiments are described to measure Q/sub 0/, Q/sub L/, and the ring power gain without additional coupling to the ring. A number of graphs are given which are useful for these measurements.     

Features and Prototypes of HTS High Q Resonant Circuit

High Te superconductor （HTS） technology has been used to develop a unique high Q resonant circuit. Such circuit or device has some special characteristics such as very high voltage generation. Theoretical study and experimental approaches have proceeded for the concept verification. This paper presents the theory about this high Q resonant circuit. The operation principle of the circuit is described. A practical prototype for HTS high voltage generation is also demonstrated. The experiment result shows that very high voltages can be achieved by the developed method using HTS technology.     

复合滤波结构的窄线宽高频微波信号产生装置

为了在较低泵浦功率下实现单纵模双波长激光信号的输出,进而获得窄线宽的高频微波信号,设计并实验了一种基于复合滤波结构的窄线宽高频微波信号产生装置。通过8字腔结构布里渊增益腔和反射式光纤光栅构成的波长选择滤波器实现了4倍布里渊频移间隔的双波长斯托克斯光信号输出,采用200 m长单模光纤作为增益介质,同时与50 m长单模光纤构成级联光纤环结构,采用三端口耦合器与2 m长未泵浦的保偏掺铒光纤构成萨格纳克环结构,利用级联光纤环结构和萨格纳克环结构的复合滤波作用实现了斯托克斯光信号模式的选择,使输出的斯托克斯光信号由多纵模运行状态变为单纵模运行状态。实验证明:通过对输出的单纵模双波长斯托克斯光信号进行拍频检测可得42.85 GHz的高频微波信号产生,线宽为38 kHz;通过改变可调谐泵浦激光器的输出波长,可实现42.25~43.51 GHz范围内的频率调谐;通过稳定性测试,产生的42.85 GHz高频微波信号的频率变化在0.83 MHz内,峰值功率变化在±0.8 dB内,稳定性良好,满足实际应用需求。     

Approximate calculation of eigenfrequencies of biconical microwave cavities

Simplified expressions are obtained for the calculation of the eigenfrequencies of a biconical cavity with large apex angles with the use of two symmetrical points at the boundaries of overlapping partial regions in the form of a spherical sector. Using these expressions, the dependence of the cavity eigenfrequencies on the apex angles of the conical elements is studied, and the results are compared with those obtained by the classical finite-element method. The applicability range of the simplified expressions is identified, and recommendations on their use are given.     

Novel technique for measuring the Q factor of thin-film lumped elements at microwave frequencies

Using higher-order resonances, it is possible to determine the Q factors of thin-film lumped elements at microwave frequencies. This technique avoids any perturbation of the experimental arrangement which normally arises from insertion and removal of the unknown.     

Properties of microwave cavities for radiometric temperature measurement.

Cavity-type coupling structures can be used for industrial microwave radiometric temperature measurement in lossy dielectrics. The cavity properties which determine the measured radiometric signal are defined and applied, and a simple technique for measuring these properties is described.     

Resonant frequency analysis of dielectric ring resonators

The mode-matching technique is applied to guided and continuous spectra to derive the resonant frequencies of the high-order azimuthal modes of dielectric ring resonators. The numerical results of this field theory analysis are in close agreement with the measurements in the X-band     

Measurement of Short Time Changes of Cavity Q and Resonant Frequency

A method for the determination of short time changes of Q factor and resonance of a cavity has been developed. The method is based on the observation of the change in reflection coefficient. As long as the cavity is coupled undercritically there always exist two frequencies at which no change of the reflection coefficient occurs. The measurement of these frequencies is sufficient for evaluating the changed values of the unloaded Q and the resonant frequency assuming no change of the external Q during perturbation. This assumption can be made in most cases of application. If there also exists a perturbation of the external Q, the value of the changed reflection coefficient must be measured at any additional freqnency preferably at the resonant frequency of the unperturbed cavity. Experimental results demonstrate the applicability of this method.     

Q value analysis of microwave photonic filters

This paper first presents the fundamental principles of the microwave photonic filters.As an example to explain how to implement a microwave photonic filter, a specific finite impulse response (FIR) filter is illustrated.Next, the Q value of the microwave photonic filters is analyzed theoretically, and methods around how to gain high Q value are discussed.Then,divided into FIR filter, first-order infinite impulse response (IIR) filter, and multi-order IIR filter, several novel microwave photonic filters with high Q value are listed and compared.The technical difficulties to get high Q value in first-order IIR filter and multi-order IIR filter are analyzed concretely.Finally, in order to gain higher Q value, a multi-order IIR microwave photonic filter that easily extends its order is presented and discussed.     

Resonant frequency of a tunable rectangular patch antenna

The uniform transmission-line model is applied to determine the resonant frequency of a coaxial probe fed rectangular patch antenna tuned by a number of passive metallic posts suitably placed within the antenna's boundary. An approximate expression is given for the resonant frequency as a function of the post location and number, and of the other characteristic parameters of the antenna. Theoretical results are compared with available measured values.     

RL-C谐振电路阻抗与Q关系的探讨

本文以归一化频率 为变量,推导了RL-C谐振电路阻抗的模|Z|与Q及 的关系表达式,并推导给出了阻抗的最大值发生时的归一化频率 与Q的关系式。通过举例进一步分析了谐振点处阻抗与阻抗的最大值发生的频率及相对误差随Q的变化而变化的规律。     

Optical fiber Fabry-Perot cavities and recirculating delay lines astunable microwave filters

The radio frequency or microwave responses of single-mode fiber Fabry-Perot cavities and recirculating delay lines are studied. It is shown that fiber Fabry-Perot cavities may be used as bandpass filters and the recirculating delay lines as bandstop filters at radio or microwave frequencies. These electric filters are tunable by electrooptic effects since the bandpass or bandstop characteristic changes when the cavity or the delay line length is varied by a few tenths of an optical wavelength. The ultimate limit on speed of tuning is set by the coherence time of the light source. The dependence of the filter responses on the spectral purity of light is studied. Examples are given to illustrate the tunability of these electric filters. The availability of various components required to build the tunable RF or microwave filters is reviewed     

Resonant frequency of circular microstrip antennas with and withoutair gaps

An improved analytical model is presented for calculating the resonant frequency of circular microstrip antennas with and without air gaps. Unlike the previous models, the present one is widely applicable to all patch diameters-from very large to very small compared to the height of the dielectric medium below the patch and also to the substrates covering the entire range of dielectric constants. The computed results for different antenna dimensions and modes of resonance are compared with the experimental values     

Resonant frequencies of open and closed loop frequency selectivesurface arrays

The effects on the transmission responses of loop element frequency selective surface arrays of breaking the conductor at suitable locations are described for simple squares and for highly convoluted geometries based on Peano curves. This simple modification generates a large reduction in the reflection band frequency for a fixed unit cell size     

Q factor, Q stability and gain in active filters

This letter sets out a simple theory relating the maximum Q factor of a second-order active-filter section to the stability of that Q factor and the available gain in the active elements used. The theory is shown to apply to both the `negative-feedback? or `Rauch?-type filters and `positive-feedback? or `Sallen?Key?-type filters and by implication to negative-impedance convertors (n.i.c.s) and the whole family of circuits based on minimum-phase feedback networks.