Measurement of Bandwidth of Microwave Resonator by Phase Shift of Signal Modulation

Bandwidth is measured by transmission of a signal with sine-wave modulation through a microwave resonator under test. The modulation frequency is adjusted so that the envelope is delayed 45/spl deg/ with respect to the input, indicating that the two sideband frequencies are separated by the half-power bandwidth. The resonance ratio (Q) is then equal to the ratio of carrier frequency over twice the modulation frequency. This depends on observations of these frequencies and the modulation phase shift, but not on the amplitude. It is insensitive to detuning or incidental frequency variation of the resonator or the signal. In a resonant cavity tested, an observed bandwidth of 30 kc at 700 mc indicated that Q =23,300.     

Dielectric property measurement using a resonant nonradiative dielectric waveguide structure

This letter describes a new dielectric characterization technique, based on the resonant nonradiative waveguide structure described by Yoneyama and Nishida , for permittivity measurements at microwave and mm-wave frequencies. The measurement system is modeled as a resonator comprised of two parallel conducting plates with a rectangular dielectric slab sandwiched in-between. Resonant frequencies of the longitudinal section electric (LSE) modes and the unloaded Q of the cavity are used to determine the permittivity of the dielectric and its loss tangent, respectively. The technique is shown to be accurate for measuring the dielectric properties of a wide array of polymer and oxide materials. For materials with small dielectric loss tangents, an accuracy of better than /spl plusmn/0.4% is attained in the measurement of the relative dielectric constant of the material.     

General Treatment of Klystron Resonant Cavities

Klystron resonant cavities are treated for general cases and their equivalent circuits are theoretically determined, which allows a fairly accurate estimate of resonant properties. It is shown that a reentrant cavity is expressed as a low-frequency series LCR/sub se/ circuit or a shunt LCR/sub sh/ circuit, taking L as the inductance of a toroidal coil with one turn and with a cross section the same as the cavity, C as the gap capacitance plus the equivalent capacitance of the cavity, and R/sub se/ or R/sub sh/ as the equivalent series or shunt resistance of the cavity at resonance. The introduction of the equivalent cavity capacitance has proved to be very effective. The formulas derived here enable one to calculate the resonant frequency within an error of a few per cent and the shunt resistance and the Q within an error of several tenths of a per cent in most cases, and thus should prove to be very useful to the designer of microwave circuits.     

Measurement of magnitude and phase of harmonics generated innonlinear microwave two-ports

A method for simultaneously measuring the magnitude and phase of the harmonics generated by a microwave two-port is reported. The two-port under test is driven with a sinusoidal microwave signal strong enough to force it into nonlinear operation. Its output harmonics are measured in the frequency domain with a setup that includes a vector network analyzer. For phase calibration at the harmonic frequencies, a millimeter-wave Schottky diode is used as a reference device. The system allows the measurement of harmonics with a phase accuracy of about ±10° at 20 GHz (referred to f₁=5 GHz). It can be built for any frequency (<40 GHz) at which a vector network analyzer and a suitable signal generator with multiplier are available. For low-amplitude harmonics, higher sensitivity compared to time-domain measurements with a sampling scope results in better measurement accuracy. The accuracy should improve further if the nonideality of the diode reference circuit is characterized more precisely     

A theoretical investigation of the resonance damping performance of magnetic material coating in power/ground plane structures

Power bus structure, consisting of two parallel solid power and ground planes separated by an insulator, behaves as a cavity resonator at high frequencies. Noise on the power bus, due to a sudden change in the current drawn by an active component, can appear as an undesired spatial fluctuation in the voltage between power and ground, especially at resonant frequencies of the resultant cavity, which may lead to problems in signal integrity, excessive delays, false switching, and radiated emission. These resonances can be suppressed by introducing high-frequency loss into the structure. This paper investigates a simple method to reduce self-/transfer impedance of power/ground planes for mitigating power/ground bounce in high-speed printed circuit board design by adding a thin layer of magnetic material coating to the inside-facing surfaces of copper power and ground plates to increase their effective high-frequency surface impedance. The increased surface impedance will increase the attenuation constant of the propagating wave inside the cavity that benefits reduction of cavity's quality factor (Q factor). The simulation results obtained from a modified cavity resonator model show that increasing surface impedance can dramatically reduce self- and transfer impedances at board resonant frequencies.     

A Dielectric Resonator Method of Measuring Inductive Capacities in the Millimeter Range

A novel technique for the measurement of dielectric and magnetic properties of a homogeneous isotropic medium in the range of approximately 3 to 100 kmc is described. An accuracy of /l.chemc/ 1 per cent is possible in the determination of permittivity or permeability in those cases where the loss tangent is sulliciently small. The measuring structure is a resonator made up of a right circular cyndrical dielectric rod placed between two parallel conducting plates. For measurement of permittivity two or more resonant TE/sub onl/ mode frequencies are determined whereas for the measurement of permeability two or more resonant TM/sub onl/ mode frequencies are determined. The dielectric or magnetic properties are computed from the resonance frequencies, structure dimensions, and unloaded Q. Since the loss tangent is inversely proportional to the unloaded Q of the structure, the precision to which Q is measured determines the accuracy of the loss tangent.     

Estimation of Q-factors and resonant frequencies

We estimate the quality factor Q and resonant frequency f/sub 0/ of a microwave cavity based on observations of a resonance curve on an equally spaced frequency grid. The observed resonance curve is the squared magnitude of an observed complex scattering parameter. We characterize the variance of the additive noise in the observed resonance curve parametrically. Based on this noise characterization, we estimate Q and f/sub 0/ and other associated model parameters using the method of weighted least squares (WLS). Based on asymptotic statistical theory, we also estimate the one-sigma uncertainty of Q and f/sub 0/. In a simulation study, the WLS method outperforms the 3-dB method and the Estin method. For the case of measured resonances, we show that the WLS method yields the most precise estimates for the resonant frequency and quality factor, especially for resonances that are undercoupled. Given that the resonance curve is sampled at a fixed number of equally spaced frequencies in the neighborhood of the resonant frequency, we determine the optimal frequency spacing in order to minimize the asymptotic standard deviation of the estimate of either Q or f/sub 0/.     

Size Effect in the Measurement of Microwave Permeability of Ferrites (Correspondence)

In the usual method of measuring the tensor permeability of ferrites at microwave frequencies, a small sample of the material is placed in a suitable cavity, and the change in resonant frequency and Q of the cavity, caused by the presence of the ferrite, are measured. The measured quantities are related to the quantities of interest-real and imaginary parts of permeability-by equations derived through perturbation theory.     

Automatic measurement of microwave-cavity parameters using stable sampled control loops

An automatic device is described which allows the continuous measurement of the resonant frequency and Q factor of a microwave cavity to accuracies within 100 parts in 106 and a few per cent., respectively.     

Design of superconducting MRI surface coil by using method of moment

A method of moment with an enhanced model to design high-temperature superconductor (HTS) RF surface coils for magnetic resonant image (MRI) is presented. The resonant frequency and quality factor (Q) of HTS RF spiral coils are simulated using this method. The agreements of resonant frequencies and Qs between the simulation and measurement are excellent with differences less than 1 % and 3 %, respectively. The 0.2-/spl mu/ m-thick YBaCuO (YBCO) thin films are deposited onto single side of 0.508-mm-thick LaAlO/sub 3/ (LAO) and sapphire substrate and patterned into a spiral shape. To accurately analyze the resonant frequency and Q of a coil, an enhanced two-fluid model is employed. HTS RF coils with diameter of 65 mm for 0.2 T and 1.5 T MRI systems are designed and fabricated with the measured Q of 19 K and 23 K, respectively. In addition, the shift of resonant frequency due to the mutual coupling between two HTS spiral coils is predicted by this method, which is important for design of HTS coil arrays in an MRI system.     

Frequency-Domain Shuttle-Pulse Measurement of Losses and Mode Conversion

A new method for measuring losses and mode conversion at microwave frequencies is presented. The method consists of producing the impulse response of single- or double-cavity resonant circuits in the frequency domain. To obtain this response, the input reflection coefficient of the circuit to be measured is first changed into a function of time by a swept-frequency technique, and then Fourier-transformed by means of a spectrum analyzer system. High generality of application and repeatability as well as measurement simplicity and definition are the main features of the new method. The examples of application presented include measurement of microstrip-line attenuation constants up to X-band and characterization of mode conversion coefficients in overmoded circular waveguide at millimeter-wave frequencies.     

Extension of Digital Automatic Method for Measuring the Permittivity of Thin Dielectric Films (Short Papers)

The permittivity of thin dielectric films can be measured with good accuracy by employing a method recently reported by the authors, whereby the microwave oscillator frequency is automatically locked to the resonant frequency of the test cavity perturbed by the sample, thus leading to a digital readout of the frequency. However, the method is satisfactory only when the frequency shift caused by the presence of the test sample does not exceed the frequency lock-in bandwidth. By employing a search oscillator, controlled by the second harmonic of the modulation signal provided for the frequency locking, this limitation is removed, thus extending the capability of the method to thicker films and/or larger permittivities.     

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.     

Nonlinear Resonant Circuits for Microwave Low Power Limiters

The letter comprises an analysis of nonlinear coupled resonant circuits for application in limiting low power microwave signals. It presents a novel approach to the use of the resonant circuit containing a nonlinear element which concerns obtaining power dependence of the quality factor and transmission losses without tuning resonant frequency. The basic theory of the single circuit is presented and examples provided of simulations in Microwave Office and measurements results of the designed two-stage limiter. The effect of transforming the input signal amplitude causes this type of circuit to be power-sensitive and allows to limit low power signals.     

LSA operation of GaAs layers in large-scale tunable microwave circuits

It is shown that the attainment of LSA oscillations in epitaxial layers of GaAs does not rely on operation of the layers in small primary resonant circuits. Restrictions on circuit dimensions have thus been relaxed and LSA oscillations obtained in large scale microwave cavities. Layers of thickness 9-12.5 microns have been operated at frequencies from 26.5-40 GHz, the oscillations being tuned over this band by a conventional short-circuit plunger. The frequency of LSA oscillation is shown to be determined entirely by the natural circuit frequency. The tuning characteristics of the oscillations in various waveguide circuits are described and some general circuit features emerge which are of importance for a tunable LSA source. In particular it is noted that in some circuits a localized and therefore fixed frequency resonance occurs. It is also noted that LSA oscillations cannot occur if circuit Q is insufficiently high. The work has been carried out on a pulse basis to avoid thermal effects, and most of the experiments described have been carried out using unencapsulated devices. The maximum efficiency observed in these experiments was 4 percent.     

The Packaged and Mounted Diode as a Microwave Circuit

Suitable definitions of the elements in the equivalent circuit of a packaged diode yield a lumped-element circuit with an impedance at its terminals which is the same as the total radial-line impedance of the packaged diode with the outer surface of the diode taken as the terminal surface. Consideration of the packaged diode as a radial-line structure permits an analytical justification for the incorporation of the diode circuit with the circuits of waveguide, coaxial-line, and strip-line diode mounts. As a result, the lumped-element equivalent circuit of a packaged diode can be directly related to the microwave equivalent circuit of the diode and the mount together. Diode element values, which were obtained from low-frequency measurements, have been used in conjunction with the theoretically determined circuits of mounted diodes to predict resonant frequencies at X-band of waveguide, coaxial-line, and stripline mounts holding packaged diodes. Similarly, antiresonant frequencies of greater than 20 Gc/s have been predicted for diodes in a radial cavity. The validity of all these predictions has been verified by measurement.     

一种数字控制电感测量仪的设计与实现

设计了一个以芯片STM32F407ZGT6为控制核心的数字式电感测量仪,可以对正弦信号源、电感Q值以及电感值实现精确测量。系统硬件电路主要由电源供电电路、信号产生电路、信号调理、测量电路、数据采集与处理以及人机交互等模块组成,其中信号调理电路采用高速运放进行放大和阻抗变换,调节信号幅度的同时保证各级的输入输出阻抗,以达到最高的测量精度。测量电路采用谐振法测量回路谐振频率,然后用伏安法测量可变电容当前值,再通过谐振频率和电容值计算得到被测电感的Q值和电感值。最后经过测试,系统实现了输出范围达50～40MHz 的正弦信号源,测量误差优于0.1%,并且对电感Q值和电感值的测量误差均小于3%。     

激光冷却铷原子喷泉钟的微波谐振腔设计

对自行研制的激光冷却铷原子喷泉钟的微波谐振腔进行了分析和设计,确定了需要的微波谐振腔基本参数。对影响微波谐振腔共振频率的因素进行了分析和研究,得到了共振频率随环境因素的变化规律。这些对调节微波腔共振频率和提高原子钟的准确度有重要意义。还对研制的微波谐振腔进行了测试,结果表明微波谐振腔的性能满足激光冷却铷原子喷泉钟的要求。由测试结果进一步估算了微波谐振腔引起的横向腔相移。     

基于高次谐波体声波谐振器的微波振荡器设计

基于高次谐波体声波谐振器(HBAR)的高品质因数(Q)值和多模谐振特性,设计了Colpitts和Pierce两种形式的微波振荡器。采用HBAR与LC元件组成谐振回路的方法,与放大电路构成反馈环路直接基频输出微波频段信号。Colpitts振荡器输出信号频率为980 MHz,信号输出功率为-4.92dBm,信号相位噪声达-119.64dBc/Hz@10kHz;Pierce振荡电路输出信号频率达到2.962GHz,信号输出功率为-9.77dBm,信号相位噪声达-112.30dBc/Hz@10kHz。     

Study of Fabry-Perot Cavities with Metal Mesh Mirrors Using Equivalent Circuit Models. Comparison with Experimental Results in the 60 GHz Band

The equivalent circuit modelling technique is used to study the resonant frequency and Q factor of plane parallel Fabry-Perot cavities with square aperture metal mesh mirrors. Comparison of different models found in literature with experimental data in the 60 GHz band is given for thin and thick cavities. Chen's model is shown to give a good agreement with measurements, as long as the cavity is not too selective and for large enough cavity.