Near-field gain of a horn and an open-ended waveguide: Comparison between theory and experiment

Generating a standard electromagnetic field requires knowledge of the gain of the transmitting antenna. The theory and supporting experimental measurements of the near-field gain of a pyramidal horn and an open-ended waveguide (OEG) at 450 MHz are given. The empirical near-field gain for the OEG is derived from experimental results obtained by a two-antenna method at about 2 GHz. The theoretical nearfield gain for the rectangular pyramidal horn is derived from Schelkunoff's formula. Two independent near-field gain measurements of these antennas are made using a three-antenna method and a transfer-standard-probe method. The discrepancy between theoretical and experimental results is typically less thanpm 1dB.     

Near-zone gain of open-ended rectangular waveguides

Full-wave solutions to the problem of radiation by open-ended rectangular waveguides (OEG) are presented. The radiation problem is formulated in terms of an electric field integral equation (EFIE). The EFIE is solved using the method of moments for three OEG antennas covering the frequency range from 200 to 750 MHz. Results for the near-zone gains as a function of both frequency and distance from the OEG aperture are presented. Estimates for uncertainties in the calculated gain are also given     

Comments on “Near-zone gain of open-ended rectangularwaveguides” [and reply]

The author comments that formulating the problem of radiation from open-ended rectangular waveguides (OEG) using an electric field integral equation (EFIE), Kawalko and Kanda (see ibid., vol.39, p.408-13, 1997) present results for the near-zone gains as a function of both the frequency and distance from the OEG aperture. These values can be considered to be exact. On the alternative methods, this paper observes that the approximate formulas need the measured values of the aperture reflection coefficient and the total radiated power. Kawalko and Kanda reply that the formula for the on-axis gain presented by Selvan (see Inst. Electron. Telecommun. Eng. J. Res., vol.43, p.61-4, 1997) certainly has an advantage over Yaghjian's formula (1984) in that it does not require knowledge of the total radiated power or the reflection coefficient at the aperture. However, this formula still does not account for all of the diffraction effects that occur at the aperture of the OEG     

Model identification in rapid thermal processing systems

Of the various techniques for controlling the temperature in rapid thermal processing (RTP), model-based control has the greatest potential for attaining the best performance, when the model is accurate. Some system identification methods are introduced to help obtain more accurate models from measured input-output data. For the first identification method, techniques for estimating the parameters (time constant and gain) of a particular physics-based model are presented. For the other, it is shown how to use the input-output measurements to obtain a black-box (autoregressive exogenous) model of the RTP system, which turns out to have better predictive capability. For each problem, the theoretical derivation of the identification technique and assumptions on which it is based are summarized, and experimental results based on data collected from an RTP system are described. Studying the DC response using the identified model led to a reconfiguration of the chamber geometry of the existing RTP system to more effectively distribute the light energy from the lamps     

Corrugated spherical antenna

The radiation characteristics of a corrugated metallic sphere with an azimuthal slot are studied. For the purpose of analysis, a dielectric coating equivalent to the corrugation on the surface is assumed. Expressions for the equivalent relative permittivity, input admittance, gain and radiated far field, based on the boundary-value approach, are presented. For a spherical antenna of k0a = 4.9087 with corrugation corresponding to an equivalent dielectric coating of relative permittivity 8.36, it is shown that the increase in gain over the uncorrugated antenna is 6.15 dB. The above antenna was fabricated and the experimental pattern obtained is compared with the theoretical result.     

Accurate measurement of antenna gain and polarization at reduced distances by an extrapolation technique

A new technique is described for determining power gain and polarization of antennas at reduced range distances. It is based on a generalized three-antenna approach which, for the first time, permits absolute gain and polarization measurements to be performed without quantitative a priori knowledge of the antennas. The required data are obtained by an extrapolation technique which includes provisions for rigorously evaluating and correcting for errors due to proximity and multipath interference effects. The theoretical basis provides a convenient and powerful approach for describing and solving antenna measurement problems, and the experimental method employed illustrates the utility of this approach. Examples of measurements are included which exhibit errors in gain as small aspm0.11dB (3sigma).     

Analysis of cavity-backed aperture antennas with a dielectricoverlay

A full-wave analysis of cavity-backed aperture antennas with a dielectric overlay is presented. The theoretical approach uses a closed-form dyadic Green's function in the spectral domain. The aperture equivalent magnetic currents are obtained using the surface equivalence theorem and an integral equation is obtained by matching the fields across the aperture. The moment method applied in spectral domain analysis is employed to solve the integral equation for the equivalent magnetic currents with proper combination of subdomain or entire domain expansion functions. Numerical results include the aperture field distribution and antenna parameters such as input impedance, bandwidth, and efficiency. A set of measurements data is compared with results based on the theoretical work     

The chemical oxygen iodine laser in the presence of a magneticfield. I. Gain measurements and polarization effects

For pt.II, see ibid., vol.29, no.3, p.944-53 (1993). The results from a combined experimental/theoretical investigation of the influence of a magnetic field on the gain and polarization in a supersonic chemical oxygen laser are described. Theoretical calculations are presented for the normalized gain as a function of magnetic field strength and are shown to be in good agreement with the experimental data. Experimental results are given for the gain suppression for P and S polarization over the range 0-1000 G. Without polarizing elements internal to the laser cavity the degree of P polarization was measured for field strength from 0 to 200 G, and a qualitative explanation is offered for the observed behavior     

Detailed transfer matrix method-based dynamic model formultisection widely tunable GCSR lasers

A theoretical model suitable for both static and dynamic analysis of widely tunable multisection grating assisted codirectional coupler with rear sampled grating reflector (GCSR) lasers is described in this paper. For the first time wide static tunability as well as transient behavior of such lasers are simulated. The theoretical model is based on the transfer matrix method (TMM) in combination with multimode rate equation analysis and takes into account a number of physical processes in the laser cavity such as longitudinal mode spatial hole burning, nonlinear gain compression, and refractive index changes with carrier injection. Static and dynamic characteristics simulated using the proposed approach agree with the experimental results presented in the paper     

垂直腔半导体光放大器增益的理论分析

针对研究增益饱和时,现有的垂直腔半导体光放大器(VCSOA)速率方程模型在确定输入信号的功率注入因子方面存在难题,根据法布里-珀罗腔边界条件,从行波方程和与位置相关的载流子方程出发,引入随轴向位置发生变化的增益增长因子刻画微腔内的驻波效应,构建出VCSOA的增益模型。利用该模型通过求方程的自洽得到了腔内载流子、光子的分布,并分析了反射增益,其结果与已报道的理论及实验基本一致。     

History-Dependent Impact Ionization Theory Applied to HgCdTe e-APDs

The variation of the gain and the excess noise factor in HgCdTe avalanche photodiodes (APDs) with different junction geometries are compared with published theoretical and numerical work. It is shown that, although some features of the gain curves are reproduced, such as the constant exponential increase in the gain, the theoretical work fails to predict the observed variation of the gain as a function of multiplication layer width. In contrast, a new analytical gain model based on local impact ionization coefficients and a first direct comparison of the prediction of history-dependent impact ionization theory are shown to give a good general fit to the experimental gain data. A generic model of the gain in HgCdTe APDs has been obtained by fitting the analytical local model to gain curves of APDs with various geometries and cut-off wavelengths. The study of different hypotheses on the electric field dependence of the dead-space length and the saturation value of the impact ionization coefficient has shown that a variable dead-space effect has a direct impact on the excess noise of APDs, which is why exact excess noise measurements are necessary to achieve a pertinent estimation of the nonlocal impact ionization function.     

Modeling of gain in erbium-doped fiber amplifiers

An analytic method is described for fully characterizing the gain of an erbium-doped fiber amplifier (EDFA) that is based on easily measured monochromatic absorption data. The analytic expressions presented, which involve the solution of one transcendental equation, can predict signal gains and pump absorptions in an amplifier containing an arbitrary number of pumps and signals from arbitrary directions. The gain of an amplifier was measured over a range of more than 20 dB in both pump and signal powers. The measured theoretical results agreed to within 0.5 dB. Although the results described apply explicitly to EDFAs pumped in the 1480-nm region, they are also applicable to EDFAs pumped in the 980-nm region. The method is valid whenever the gain saturation by amplified spontaneous-emission noise can be neglected, which is typically the case for amplifiers with less than about 20 dB of gain     

Using hardware gating to improve antenna gain measurements incompact antenna range

Results are presented for antenna gain measurements in a compact antenna range at a frequency below the minimum specified operating frequency of the range. Hardware gating is used to reduce clutter or unwanted scattering from the backlobe of the feed and the walls of the chamber. Measured time domain data are presented which prove that these stray signals can be eliminated from the incident field in the test zone, and frequency data are presented to show the improvement in measured antenna gain     

Maximum Rate of Frequency Scanning for Distortionless Signal Generation in Electromagnetic Reverberation Chambers

We derive theoretical and experimental performance based upper bounds for the rate of frequency scanning (sweeping) or electronic stirring inside a reverberation chamber. The interior field is modeled as a dynamic process of frequency modulation of the source field. The bounds are obtained by imposing quasi-stationarity of the field, as a requirement for preventing nonlinear distortion of an analog or digital excitation (test) signal injected into the chamber.      

Soliton—Voltage and phase characteristics of a microwave crossed-field amplifier

The soliton approach to solving a nonlinear, partial differential equation which describes the operation of a crossed-field amplifier is extended to include all dc magnetic field values, all operating frequencies, and all three spatial dimensions. Theoretical predictions of voltage characteristics are shown to agree with the experimental data for a large variety of cases. Equations for phase shift are discussed in depth with experimental data presented to demonstrate a close correlation with theoretical predictions.     

Output power characteristics of erbium-doped fiber ring lasers

The output power of an erbium-doped fiber ring laser has been measured as a function of pump power, emission wavelength, doped-fiber length, and reflectivity of the output coupler. A theoretical model for the calculation of the output power is introduced that is based on a previously derived gain equation for erbium-doped fiber amplifiers. The calculated values are in good agreement with the experimental data, confirming the applicability of the theory to a reliable modeling of the output power of erbium fiber ring lasers     

Analysis of a cylindrical antenna containing an aperture coupledload

In this paper we present the basis for the analysis of shielded tuning networks coupled to wire antenna elements. The structure analyzed comprises three conducting cylindrical tubes that form an aperture-fed circular coaxial waveguide. Two methods are presented for formulating and solving integral equations for the structure. The first method is based on the mixed potential electric field integral equation enforced on the three cylindrical tubes, and the second is based on aperture theory. An end correction capacitance is used to adjust the reflection coefficient in the eigenmode expressions of the aperture method. The data obtained by the two methods are in close agreement. Differences in actual currents and equivalent currents obtained from solutions are discussed and reconciled     

Gain nonlinearities due to carrier density dependent dispersion insemiconductor lasers

Semiconductor-field interaction is analyzed by using a semiclassical density-matrix approach. Using an exact elimination procedure for the dipole moments, corrections to the standard rate equation are obtained and shown to result in gain nonlinearities. The gain nonlinearities are due to carrier-density-dependent dispersion at the lasing frequency. Using available measured data of the frequency dependence of the carrier-induced refractive index change, gain compression coefficients in agreement with experimental values are obtained     

消声室声场分析模型探讨

讨论了影响消声室声场的因素,给出了消声室声场的判据,对消声室内声场的计算提出了看法并采用OEDON软件对南京大学消声室的声场进行建模计算,结果与理论及实测结果较为一致,并对认为低频截止频率没有意义的观点提出了不同意见.     

Laser Dynamics of a 10 GHz 0.55 ps Asynchronously Harmonic Modelocked Er-Doped Fiber Soliton Laser

Laser dynamics of a 10 GHz 0.55 ps asynchronously harmonic modelocked Er-doped fiber soliton laser are investigated both theoretically and experimentally. Theoretical analyses based on the master equation model solved by the variational method have indicated that all the pulse parameters of the laser output will exhibit complicated slow periodic variations in the asynchronous soliton modelocking (ASM) mode. New experimental methods based on analyzing directly the RF spectra of the ASM laser output have been developed to accurately determine the sinusoidal variation of the pulse timing and the pulse center wavelength for the first time. It is found that the pulse center wavelength variation can be as large as 1 nm half-peak-to-peak and the pulse timing variation can be as large as 3 ps. The consistency among all the experimental data and theoretical prediction is carefully examined and the results indicate that the ASM pulse dynamics observed experimentally are in good agreement with those obtained from the theoretical analyses.