On the resonant frequencies of microstrip antennas

An appropriately corrected formula for the resonant frequencies of microstrip antenna elements is obtained that is based on the evaluation of the average value of the effective dielectric constant. The author describes the integration averaging technique and presents two examples of its use in more accurately calculating the resonant frequencies of the first five modes of an equilateral triangular microstrip antenna     

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/.     

On the resonant frequencies of the triangular patch antenna

The appropriate correction factor to use in the resonant frequency formula of an equilateral triangular patch antenna obtained from the cavity model with perfect magnetic walls is discussed.     

Theory of resonant modulation at millimeter wave frequencies ofinhomogeneously biased monolithic quantum-well lasers

We show theoretically that resonant modulation at millimeter wave frequencies of inhomogeneously biased monolithic quantum-well laser diodes provides an enhancement in the modulation efficiency of >14 dB over that of the homogeneously biased laser, accompanied by a corresponding 7 dB increase in the noise and a comparable decrease in the signal-to-intermodulation distortion. We derive simple expressions for the enhancement in the modulation efficiency, the noise and intermodulation distortion, and discuss the limits of this approach and the trade off between these quantities. The theoretical results presented here are in good agreement with recently published experimental work     

Comments on “On the resonant frequencies of microstripantennas”

The resonant frequencies of equilateral triangular microstrip antenna calculated by Gang (see ibid. vol.37, no.2, p.245, 1989) are compared with the experimental results of Dahele and Lee (1987). When computing the resonant frequencies of equilateral triangular microstrip antenna, using the same equations proposed by Gang, we obtained different results, which are given, from Gang's results. For an equilateral triangular microstrip antenna, the resonant frequencies obtained from the cavity model with perfect magnetic walls are given by the formula shown. In this work, we suggest a new closed-form expression. We compared our computed values of the resonant frequencies for the first five modes of the equilateral triangular patch antenna with theoretical and experimental results reported by other scientists     

Improved formulae for the resonant frequencies of triangular microstrip patch antennas

In this article, an improved formula for the effective side length (a _eff) of the equilateral triangular patch antenna is presented. The computed resonant frequencies for the first five modes, using this formula, are compared with the available experimental and theoretical results in the literature. It is shown that the proposed formula has better accuracy than other available expressions. Moreover, the 30°–60°–90° and 30°–30°–120° triangular patch antennas are studied. Specifically, improved formulae for the effective dielectric constant of these patches are derived.     

An improved formula for the resonant frequencies of the triangularmicrostrip patch antenna

An improved version of a formula due to J.S. Dahele and K.F. Lee (ibid., vol.AP-35, p.100-101, Jan. 1987) is presented for predicting the resonant frequency of a triangular microstrip patch antenna. Using a different effective length and the actual substrate permittivity, the technique previously used for the case of a circular disk is modified to produce greater accuracy than previously reported in the literature. This method consistently predicts resonant frequencies more accurately through the first five resonances     

Complex resonant frequencies of biological targets for microwave imaging applications

The authors report on the complex resonant frequencies of a lossy dielectric sphere immersed in a lossy dielectric medium and their potential application to the classification of suspicious growths in breast cancer diagnosis using microwave imaging.     

A comparison of models to determine the resonant frequencies of arectangular microstrip antenna

Three variations of the cavity model for determining the resonant frequencies of a rectangular microstrip antenna are compared. The results for each of the variations were experimentally verified by studying a set of patched antennas fed to excite different modes. The method's applicability to electrically thick rectangular microstrip antennas was also investigated. It is also shown that the uncertainties of the patches' dimensions and substrate properties can greatly affect the final result     

Determination of plasma electron-density distribution from the resonant frequencies of a parallel-plate cavity

A microwave resonant cavity method of plasma diagnostics is demonstrated for a parallel-plate cavity containing a cold, collisionless, and isotropic plasma. The method is extended to more general cavities and plasmas in the Appendix. The approach presented here differs from perturbational formulations in that assumptions about the perturbed fields are not made. The analysis gives an exact relation between the electron-density distribution and the resonant frequencies. Laboratory measurements of resonant frequencies then allow a spatially detailed computation of the electron-density distribution. Results are found to agree well with Langmuir probe measurements.     

Computation of resonant frequencies of dielectric loadedrectangular cavity using TLM method

The electromagnetic analysis of a dielectric loaded rectangular cavity using the 3D transmission line matrix method is presented. It is found that in order to excite all the modes within a frequency range, the field polarisation and location of the excitation brick in the TLM analysis must be properly selected. For the resonator of concern, the results of computation of the first 11 resonant frequencies show excellent agreement with the experimental results     

Theoretical and experimental studies of the resonant frequencies ofthe equilateral triangular microstrip antenna

A critical study of the resonant frequency of the equilateral triangular patch antenna is presented. The contributions include: (1) comparison of the previous experimental data of J. S. Dahele and K. F. Lee (see ibid., vol.AP-35, no.1, p.100-1, 1987) with moment method results; (2) new measurements and moment method results for ϵ_r=10.5 and comparison with Gang's hypothesis; (3) verification of the relationship among the various modes by measurements and by the moment method; and (4) a curve fitting formula yielding the resonant frequency of the lowest mode, which is within 1% of the value obtained from moment method analysis     

Determination of the resonant frequencies in a complex cavity usingthe scattering matrix formulation

A method for computing the resonant frequency in a complex cavity consisting of a series of waveguide sections is derived. The analysis is restricted to transitions in which one waveguide is wholly contained in the other. An eigenvalue problem is formed by cascading the scattering matrix from a given section outwards to the ends of the complex cavity, with appropriate boundary conditions at the ends. The eigenvalue equation is solved numerically by searching for a complex frequency, the cavity Q being determined by half of the ratio of the real to the imaginary part of the frequency. The technique is easily implemented numerically and shows good agreement with experiment. This method is suitable for modeling both abrupt changes in radius and smoothly varying tapers     

GIBC formulation for the resonant frequencies and fielddistribution of a substrate-mounted dielectric resonator

Dielectric resonators (DR's) are widely used in telecommunication systems. A method is proposed here to find the resonant frequency and field distribution in a substrate-mounted DR structure. The field of a dielectric rod has been decomposed into a combination of guided modes with unknown coefficients and an unknown continuous spectrum of radiation field. The unknowns are then obtained by applying two generalized impedance boundary conditions (GIBC's) representing the substrate and air layers at the top and bottom of the DR. This leads to the calculation of the total (guided+radiation) field as well as the resonant frequency of the structure     

Detection of respiratory sounds at the external ear

Several clinical and ambulatory settings necessitate respiratory monitoring without a mouthpiece or facemask. Several studies have demonstrated the utility of breathing sound measurements performed on the chest or neck to detect airflow. However, there are limitations to skin surface measurements, including susceptibility to external noise and transducer motion. Thus, this two-part study investigated a novel location for breathing sound measurements: the external ear. The first study investigated characteristics of sound transmission from the oropharynx to the external ear in 19 adults (nine males). Broadband noise was directed into the oropharynx through a tube and mouthpiece and measured indirectly via an accelerometer affixed to the cheek. Resultant transmission to the external ear was measured with a microphone inserted into an earplug that provided acoustic isolation from ambient noise. Near-unity coherence estimates (> 0.9) between the sounds recorded at the external ear and the oropharynx were observed up to approximately 800 Hz, indicating a low-frequency region of preferred transmission. In the second study, each of 20 subjects (nine males) breathed through a pneumotachograph at targeted shallow (3.0 mL/s/kg) and tidal (7.5 mL/s/kg) flows normalized to body mass, and the resulting sounds were recorded at the external ear. Recordings during breath hold measured background noise. Shallow and tidal expiratory flows, respectively, produced signal-plus-noise-to-noise [(S + N)/N] ratios of 6.7 +/- 4.1 dB and 14.0 +/- 5.3 dB (mean +/- standard deviation) across all subjects between 150 and 300 Hz. Concurrent inspiration demonstrated (S + N)/N ratios of 6.6 +/- 3.9 dB and 14.9 +/- 6.3 dB. Thus, the external ear shows promise as an anatomic site to detect and monitor breathing in a relatively noninvasive and unobtrusive manner.     

旋转剪切频闪散斑干涉法测量物体的固有频率

提出一种测量物体固有频率的新方法--旋转剪切频闪散斑干涉法.该方法能方便地测量振动物体的固有频率,具有较高的精度、全场显示、条纹可见度好等优点,给出了理论分析和实验结果.     

Integration equation analysis on resonant frequencies and qualityfactors of rectangular dielectric resonators

In this paper, the resonance problem of rectangular dielectric resonators (DRs) is analyzed by using the spectral dyadic Green's function and volume integral-equation formulation. The rectangular dielectric body is replaced by a set of entire-domain polarized volume current basis, and Galerkin's moment method is used to solve the resonant frequency and quality factor of the rectangular DR. The effects of electrical and geometrical parameters on the resonance of the TE₁₁₁ mode of isolated DRs are also presented. Additionally, the case of a rectangular DR with a ground plane is also discussed. Results are found to be in good agreement with the published experimental data     

Accurate resonant frequencies of cylindrical dielectric resonators using a simple analytical technique

With the Introduction of an appropriate definition of `effective dielectric constant?, a simple analytical technique is proposed for determining the resonant frequencies of isolated cylindrical dielectric resonators. Computations for the dominant mode show that this method yields results as accurate as those reported using rigorous methods.     

Application of variational principle for calculation of resonant frequencies of cylindrical dielectric resonators

In the letter we present a new method for the calculations of resonant frequencies of cylindrical dielectric resonators using the variational principle. This method is applicable for determining the resonant frequencies of cylindrical isolated and shielded dielectric resonators. Computations for all modes (TE, TM and HEM) are given.