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1.
A rectangular waveguide resonator operating in the H105 mode at 3.2 GHz is used in determining the change in resonant frequency, ΔF , and the Q factor of the cavity, ΔT , when measured with and without single corn kernels of various shapes and dimensions. By measuring those variables for a kernel oriented in two positions differing by a 90° rotation with respect to the maximum E -field vector, the average values of ΔF and ΔT are found to be independent of shape. The ratio ΔF /ΔT is independent of size and is a function of the material properties (ε'-1)/ε". This function is shown to be related to the material density, moisture content, or other characteristics when all other properties except the one selected remain unchanged 相似文献
2.
A theoretical analysis of intensity modulation in coupled waveguides and Mach-Zehnder interferometers is reported. Simultaneous phase and amplitude perturbations Δn +ιΔk are considered. Predictions are made about the performance of electrooptic GaAs and InP modulators controlled by the free-carrier effect (ΔN ) or by the Franz-Keldysh effect (ΔE ). The phase-dominant condition Δn >5Δk is optimal. The predicted depth of modulation is greater than that of conventional loss-modulators over a range of ΔN or ΔE 相似文献
3.
Theoretical and experimental studies of the evolution of a frequency-chirped pulse under the influence of both phase and gain dispersion effects induced by the free-electron laser interaction are presented. For the experimental parameters used (electron beam voltage V =150 kV, wiggler periodicity l w=3.5 cm, gain ~10 dB, input pulse width Δt ~200 ns, frequency w 0/2π=10 GHz, and frequency chirp α/2π~5 MHz/ns), pulses of a few nanoseconds were generated after an interaction length of 2.30 m, in good agreement with theoretical expectations 相似文献
4.
Xiupu Zhang Peixuan Jiang 《Lightwave Technology, Journal of》1992,10(8):1127-1131
The performance of a coherent optical M -ary continuous-phase frequency-shift-keying (CPFSK) receiver using limiter-discriminator (L-D) detection is investigated. It is shown that L-D detection of CPFSK optical signals offers the best performance for a large normalized IF beat spectral linewidth, ΔνT . When the modulation index is unity, the receiver is immune to laser phase noise and can produce (M /4) exp (-SNR) symbol error probability, which may be considered as the upper bound if the optimal modulation index is used (SNR is the signal-to-noise ratio per symbol). Optimum modulation indexes are 0.8 and 1 at ΔνT =1% and ΔνT =2%, respectively, for M =4, 8, and 16 相似文献
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The frequency of a GaAs semiconductor laser, locked to the optogalvanic signal corresponding to the 4s11-4p12 transition of Ar, was tuned in the frequency range of ±1.75 GHz by use of the Zeeman effect. The observed tuning factor of 1.60 MHz/G agreed with that calculated from the g factor in jj -coupling at a weak field case. The frequency-locking was accomplished by using a frequency discriminator obtained by Zeeman modulation 相似文献
7.
The OMDR (optical-microwave double resonance) effect in the Cs D 2 line was studied for realizing a gas-cell-type Cs atomic frequency standard. A glass cell containing Cs with buffer gases (Ar/N2=1.26, total pressure=39 torr) was placed in a TE012 mode microwave cavity at a temperature of 45°C and was pumped using a GaAs semiconductor laser frequency locked to an external interferometer tuned to the 6P3/2 (F=2,3,4)←6 S 1/2(F =3) transition. The OMDR signal appearing at the resonance to the F =4←3 hyperfine transition of the 6S1/2 state shifted with detuning of the laser frequency and with change of the laser and microwave powers. The dependence of the shift on these variables around an optimum operating condition was obtained as, ΔνMW[Hz]=-(0.31±0.02) {1+(0.44±0.15) (ΔP L/P L)} ΔνL [MHz]-10(ΔV MW/V MW) 相似文献
8.
For a TM01δ mode dielectric rod resonator placed coaxially in a TM01 cutoff circular waveguide, characteristics such as the resonant frequency, its temperature coefficient, the unloaded Q , and the other resonances are discussed on the bases of accurate calculations using the mode-matching method. The results show that this resonator compares favorably with a conventional TE01δ mode dielectric resonator, particularly for realization of a high unloaded Q . Analytical results also verify that interresonator coupling between these two resonators can be expressed equivalently by a capacitively coupled LC resonant circuit. A four-stage Chebyshev filter having a ripple of 0.035 dB and an equiripple bandwidth of 27 MHz at a center frequency of 11.958 GHz was fabricated using these resonators. Its insertion loss is 0.5 dB, which corresponds to an unloaded Q of 17000, and no spurious response appears in the frequency range below 17 GHz 相似文献
9.
Polarization-independent phase modulation in In1-xGa xAs/InGaAlAs multiple-quantum-well waveguides is demonstrated for the first time. It is shown that by increasing the Ga fraction and hence the tensile strain in the quantum well the electric-field-induced refractive index change in the TM polarization Δn TM can be made to approach that in the TE polarization Δn TE. At 1.523 μm, the ratio Δn TM /Δn TE=1 for x =0.7 with a phase shift coefficient of 17.4°/V-mm was achieved. Polarization independence was maintained over the entire range of reverse bias voltage 相似文献
10.
Ahlswede R. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1990,36(1):166-171
An attempt is made to determine whether it is true that for a fixed distortion level Δ the rate-distortion function R ( P ,Δ) has in the distribution P no local maxima with values different from the global maximum. It is shown that, in general, the answer is negative. However, the answer is positive for Hamming distortion measures. Moreover their R is Schur-concave 相似文献
11.
Using a mathematical model for nonuniform FM-response DFB lasers, the authors calculated the influence of thermal and carrier-density effects on an adaptive quantized feedback equalization circuit (AQFE). A linear networks is introduced which allows the calculation of an equivalent overall system bandwidth. The equalizer circuit is tolerant to dip frequency variations f min of the laser's frequency response from 0 to >10 MHz and amplitude variations A between 0.1 and 0.5 for f ≫f min. Hence, lasers can be equalized independent of their individual FM-response. It is calculated that an equivalent bandwidth f c of more than 1 GHz can achieved 相似文献
12.
Yiqi Zhuang Qing Sun 《Electron Devices, IEEE Transactions on》1991,38(11):2540-2547
Accelerated life tests with high-temperature storage and electric aging for n+-p-n silicon planar transistors were carried out. Current gain h FE increases monotonously with time during the tests, and the h FE drift is correlated with initial measured 1/f noise in the transistors, i.e. the drift amount significantly increases with the increase of noise level. The correlation coefficient of relative drift Δh FE /h FE and 1/f noise spectral density S iB(f ) is far larger than that of Δ h FE/h FE and initial DC parameters of the transistors. A quantitative theory model for the h FE drift has been developed and explains the h FE drift behavior in the tests, which suggests that the h FE drift and 1/f noise can be attributed to the same physical origin, and both are caused by the modulation of the oxide traps near the Si-SiO2 interface to Si surface recombination. 1/f noise measurement, therefore, may be used as a fast and nondestructive means to predict the long-term instability in bipolar transistors 相似文献
13.
In burst digital transmission using PSK (phase shift keying) modulation with coherent detection, the recovery of the carrier reference phase and the symbol clock is a key aspect. If all users have a common clock synchronization, symbol timing needs not to be recovered in each burst. A digital processor for carrier recovery without preambles, in the presence of frequency offset, is considered. As an example, a 2 Mb/s QPSK transmission system is considered in which E b/N o=10 dB, and the burst and estimation interval length L =15. Using the algorithm described and averaging eight successive estimated frequency offsets, in order to eliminate anomalous errors, the BER (bit error rate) degradation is equal to 0.14 dB when Δf =20 kHz 相似文献
14.
Roberts J.H. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1988,34(6):1483-1490
A probability density function Pm(R 1,R 2,Δ) is presented for a narrowband noise process in which R 1 and R 2 are two envelope samples and Δ is the phase difference. For m =1 the process is Gaussian, but for m =2,3, etc., it is non-Gaussian. New second-order statistical properties are identified for it as well as the density function for the resulting envelope when a signal is added to the noise. These results are given, though the major concern is with the density of the phase difference Δ and the density of &thetas;, the response of an FM detector fed with the noise 相似文献
15.
Connector contacts have a typical end-of-life behavior during accelerated life testing. A model that predicts the change in resistance (ΔR ) for an aging contact is developed based on that behavior. The model shows that the duration of accelerated life tests can sometimes be reduced by up to 50%, resulting in substantial time and cost savings. Analysis of the model leads to several unexpected conclusions. For example, the evaluation of contact reliability, using ΔR as a parameter, does not agree with a time-to-failure approach in which each individual contact is assumed to have a specific failure time. The agreement is restored by the use of change in conductance (ΔG ) ratios. The use of ΔG by itself leads directly to the conclusion that contact reliability evaluated at some point in a contact's life explicitly depends on the resistance of the contact when it was put into use 相似文献
16.
In self-aligned polysilicon emitter transistors a large electric field existing at the periphery of the emitter-base junction under reverse bias can create hot-carrier-induced degradation. The degradation of polysilicon emitter transistor gain under DC stress conditions can be modelled by ΔI B∝I R m+nt n where n ≈0.5 and m ≈0.5. The more complex relationships of Δβ(I C, I R, t ) and β(I C, I R, t ) result naturally from the simple ΔI B model. Using these relationships the device lifetime can be extrapolated over a wide range of reverse stress currents for a given technology 相似文献
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Janssen A.J.E.M. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》1992,38(1):168-171
It is shown how the Zak transform can be used to find nontrivial examples of functions f , g ∈L 2(R ) with f ×g ≡0≡F ×G , where F , G are the Fourier transforms of f , g , respectively. This is then used to exhibit a nontrivial pair of functions h , k ∈L2(R ), h ≠k , such that |h |=|k |, |H |=|K |. A similar construction is used to find an abundance of nontrivial pairs of functions h , k ∈L2 (R ), h ≠k , with |A h |=|A k| or with |W h|=|W k| where A h, A k and W h, W k are the ambiguity functions and Wigner distributions of h , k , respectively. One of the examples of a pair of h , k ∈L 2(R ), h ≠k , with |A h|=|A k| is F.A. Grunbaum's (1981) example. In addition, nontrivial examples of functions g and signals f 1≠f 2 such that f 1 and f 2 have the same spectrogram when using g as window have been found 相似文献
19.
A second-order multibit ΣΔ (sigma-delta) analog-to-digital converter (ADC) with a 4-b internal quantizer is described. It uses a simple and fast digital correction scheme. A correlated-double-sampling (CDS) fully differential integrator was used, in which the op amp needed only a low slew rate and moderate bandwidth for a sampling rate of 5.25 MHz. A second-order modulator was fabricated in the standard MOSIS p-well 2-μm CMOS process. The excellent measured linearity and high S /(N +D ) ratio (95 dB with an oversampling ratio of only 128) of the corrected converter verified the practical advantages of the proposed architecture 相似文献
20.
A bidirectional common polarization control method with a single polarization controller for a coherent optical FDM bidirectional transmission system is discussed. This method is promising for realizing a reliable and low-cost terminal in a coherent multichannel distribution system because the polarization controller can be placed in common only at a central office. Theoretical and experimental results show that the frequency separation δf has to be 6×bit rate<δf <120/Δτ (GHz) for FSK bidirectional transmission. The method is effective not only for reducing the complexity of the subscriber terminal but also for improving the reliability in a coherent CATV system 相似文献