共查询到10条相似文献,搜索用时 31 毫秒
1.
Influence of Electric Field Distribution on High-Power Array Antenna Radiation Pattern with Rectangular Aperture 下载免费PDF全文
The antenna element with rectangular aperture is one of the main forms of the array antenna. The electric field amplitude distribution of the rectangular aperture, as well as the phase distribution is the most important parameter that affects the radiation gain and beam direction of the array antenna. In this work, a theoretical study is carried out on array antennae for high-power microwave (HPM) applications. An electric integration method is applied to obtain the far-field radiation pattern with different kinds of electric field distributions. Moreover, the influence of the electric field amplitude and phase on the performance of the array antenna is analyzed. For one antenna element, uniform electric field distribution is not the best choice. However, the uniform distribution has specific advantages for an array antenna consisting of combined antenna elements. The phase deviation has more significant influence on the performance of the array antenna than the amplitude deviation. It indicates that a good working phase shifter with high-power capacity and time-adjusting capability is very important. 相似文献
2.
Generation of the second harmonic initiated by Bell-Plesset effects in a cylindrical geometry is studied analytically. For an initial single-mode velocity perturSation, the second-order mode-coupling formula is obtained by expanding the perturbation displacement and velocity potential up to the second-order accuracy. It is found that the initially symmetric interface evolves into a significant bubble-spike asymmetric pattern. The second-order solutions clearly show that the amplitude of the spike grows faster than that of the buSble. The temporal evolutions of the amplitudes of the 5ubSie and spike are dependent on the interface velocity Vo. The larger interface velocity leads to the smaller amplitude of the perturbation at an arbitrary interface position in a cylindrically convergent geometry. 相似文献
3.
QIAOWenxiao CHENXuelian DUGuangsheng FANGJun LIGang 《声学学报:英文版》2003,22(4):329-338
Two small scale acoustic phased arrays with 4 elements have been designed and assembled in the laboratory. Experiments have been carried out with them. It is found that both directivity and radiation lobe width of the phased array can be regulated by changing the time delay between the input signals on neighboring elements. Results measured are in good agreement with those calculated. By using the phased array as an acoustic transmitter and hydrophone as a receiver, small scale acoustic well-logging simulations have been carried out both on an aluminum model well and on a concrete one. Experimental results show that, by increasing the time delay of the input signals on neighboring elements, the steered radiation angle of the phased array becomes larger and larger, and generation conditions of the refracted compressional wave and the refracted shear wave are reached successively, and the refracted compressional wave, the refracted shear wave and the Stoneley wave axe strengthened, respectively. Therefore, by choosing element spacing of a phased array and acoustic wave frequency appropriately, the main radiation lobe of the phased array can be widened to cover the first critical angle of all kinds of formations, which makes it possible to apply phased array acoustic well-logging in any formation continuously without regulating directivity of the phased array. 相似文献
4.
In this paper,a sidelobe suppression method using nonuniformly spaced array with aperture apodization processing is proposed for underwater acoustic imaging in near field,which is studied both in theory and experiment.The focused beamforming based on spherical wave propagation theory is used in the method.Firstly,the nonuniform array with low sidelobe is designed for suppressing the sidelobe of one-way beam pattern by spacing perturbation.Then, applying the aperture apodization technique to underwater acoustic imaging,the different size apertures for transmitting and receiving are used for further suppressing the sidelobe of two-way beam pattern.The experimental results from water tank show that the proposed method can suppress the sidelobe more effectively only with fractional mainlobe width increase.Since the method is simple-realized,the imaging system can be simplified as well as achieving improved performance. 相似文献
5.
In this paper,experimental and theoretical studies of the output mode characteristics of an in-phase locked gain waveguide array CO 2 laser are reported.The experimental results of the optical oscillation mode frequency,the far-field intensity distribution and the burnt pattern of the sliced waveguide array laser are obtained.A revised mode expression of the rectangle waveguide,which is suited for this waveguide array CO 2 laser,is proposed.The theoretical simulation results based on the revised mode expression are shown to be in good agreement with the experimental results. 相似文献
6.
The mutual radiation impedance ignored in conventional array directivity formula is introduced into the calculation of array radiation sound field,and a modified array directivity formula considering the mutual radiation impedance is gained according to the superposition principle.Results of computer simulation and experiments for a uniform linear array and a uniform planar array show superior performance on the present of the practical directivity pattern of the modified formula in this paper in comparison to the conventional one. 相似文献
7.
Design of surface emitting distributed feedback quantum cascade laser with single-lobe far-field pattern and high outcoupling efficiency 下载免费PDF全文
A 7.8-$\mu $m surface emitting second-order distributed
feedback quantum cascade laser (DFB QCL) structure with metallized
surface grating is studied. The modal property of this structure is
described by utilizing coupled-mode theory where the coupling
coefficients are derived from exact Floquet--Bloch solutions of
infinite periodic structure. Based on this theory, the influence of
waveguide structure and grating topography as well as device length
on the laser performance is numerically investigated. The optimized
surface emitting second-order DFB QCL structure design exhibits a
high surface outcoupling efficiency of 22{\%} and a low threshold
gain of 10~cm$^{ - 1}$. Using a {$\pi $} phase-shift in the centre
of the grating, a high-quality single-lobe far-field radiation
pattern is obtained. 相似文献
8.
This paper presents a new focusing and scanning method which focuses multiple waves on a target. The key of the method is to control excitation pulses for each element of the transducer array. The excitation pulse on each array element is obtained by time reversing the signal received by the same element, which is generated by an imaginary source at the target. The excitation pulses from all array elements are transmitted and arrive at the target simultaneously, and focusing is achieved. The performance of the two methods is compared in numerical examples, and it is demonstrated that the proposed method achieves a satisfactory focusing and a good signal-to-noise ratio no matter where the target location is. 相似文献
9.
WUHao ZHANGBixing WANGChenghao 《声学学报:英文版》2005,24(1):21-32
The multi-path effect of the acoustical wave in a solid plate is studied. The multireflection and wave conversion of the cylindrical compressional and shear waves, which are excited by an infinite strip on a free surface of the solid plate, are analyzed thoroughly by the far-field approximation method. The concise analytical representations of the cylindrical waves are obtained. The time reversal processing is then applied to the propagation of the cylindrical waves and analyzed theoretically and experimentally. It is shown that the waves coming from different array elements and different paths all arrive at the original place after the time reversal operation. It indicates that the time reversal can compensate automatically the wave aberration caused by the multi-path effect. The self-adaptive focusing of the time reversal field is also analyzed quantificationally by the focusing gain and the ratio of the principal to the second lobe. The effects of the focus position and the aperture of the transducer array on the focused field are also investigated. It shows that theoretical and experimental results are consistent to each other very well. 相似文献
10.
Based on the principle of the Lorentz covariance, the transition matrix elements from an off-shell photon state to the vacuum are parameterized by the light-cone photon distribution amplitudes (DAs). Both the scalar off-shell photon light-cone DA and the corresponding coupling are calculated in the instanton vacuum model of quantum chromodynamics (QCD), and their explicit analytical expressions and the numerical results are given. The results for the other chiral-odd light-cone photon DAs and their couplings are presented as well. 相似文献