Optimum aperture monopulse excitations

A unified formulation of the optimization of monopulse antenna performance indices for a specified sidelobe envelope function and/or specified nulls of the pattern is presented. The performance indices considered are beam efficiency, gain factor, and angular sensitivity factor of rectangular and circular apertures. The unconstrained optimization of beam efficiency result in an integral equation, the solutions of which are prolate spheroidal wave functions for rectangular aperture and hyperspheroidal wave functions for circular aperture. These functions reduce, respectively, to Legendre and Zernike polynomials in the case of gain factor and angular sensitivity factor. The double orthogonality properties of these eigenfunctions are used for constrained optimization. The results obtained by this technique for the near-in sidelobes constrained at a uniform level are shown to be in agreement with the earlier works. The method is applicable for other aperture surfaces such as elliptical, ellipsoidal, and spherical.     

Analysis of diagonal horns through Gaussian-Hermite modes

The radiation characteristics of diagonal horns are investigated by means of Gaussian-Hermite modes. It is shown that, for reasonably long horns, the beamwidths in the principal and 45° planes are equal to within 10%, and all sidelobes are below -15 dB. It is also demonstrated that the phase center of a diffraction-limited horn is close to the aperture, whereas the phase center of a constant-beamwidth horn is behind the throat. The maximum coupling to the lowest order copolar Gaussian mode is 84%, and the total amount of power coupled into the cross-polarized lobes is 9.5%. More significantly, the aperture efficiency of a Cassegrain antenna fed by a diagonal horn has a maximum value of 81%, which compares with 87% for a corrugated horn. The maximum efficiency is achieved when the aperture of a diffraction-limited horn is placed at a confocal tertiary focus, although a secondary focus gives an aperture efficiency that is only 10% lower, suggesting that diagonal horns are suitable for focal-plane arrays     

A multielement high power monopulse feed with low sidelobe and high aperture efficiency

A multielement high power monopulse feed was investigated for excitation of a phased array. This feed has the advantages of high antenna efficiency, effective independent sidelobe control for the sum and difference patterns, and high power handling capability. A 32-element device has been designed which yields theoretical sidelobe levels less than -31 dB for both the sum and difference patterns over the 2800 to 3200 MHz frequency band. The aperture efficiency is 69.5 percent which includes 0.1 dB spillover loss and 1.40 dB tapering loss. The difference slope efficiency defined as the actual slope gain over the maximum possible value is 50 percent at midband. An experimental feed was constructed to verify the predicted performance characteristics. Measured data on both the radiation patterns and the antenna gain agreed very Well with the analytical results. The measured sidelobe level is below -30 dB for all sum and difference beams over the 2800 to 3200 MHz. In addition, this feed can be designed for low power intensity at the feed aperture so that very high power operation can be attained.     

Estimating aperture efficiency

It is shown that for a wide class of aperture distributions, the aperture efficiency can be related to the ratio between the beamwidth of this distribution and that of the uniform one. A heuristic rule for estimating the aperture efficiency of elliptic and rectangular tapered apertures is introduced. It is shown that, if the beamwidth is given (i.e., the aperture size is unconstrained), the maximum directivity is provided by a tapered, rather than uniform amplitude distribution.     

Power transfer efficiency between focused circular antennas with Gaussian illumination in Fresnel region

The power transfer efficiency between two circular aperture antennas in the Fresnel region is obtained analytically and explicitly. They are focused at each other and illuminated as a simple Gaussian taper. Two apertures also have generally different sizes and unequal illuminations. It is shown that the Gaussian distribution is close to the optimum, which is derived from the theory of the confocal optical resonators. The effect of the deviation of the illumination from the optimum upon the efficiency is numerically evaluated. The result shows that the reduction of the efficiency for a constant deviation increases as the Fresnel number decreases. The dissimilarity of both aperture illuminations also reduces the efficiency. The qualitative trend is such that the larger the dissimilarity, the smaller the efficiency. When the order of dissimilarity is small or the taper of the aperture is large, the efficiency can be approximately predicted by assuming equal illumination with the geometrical mean of the two illuminations. A simplified approximate efficiency which can be applied to the greatly tapered illumination is also derived.     

Factorization of the feed efficiency of paraboloids and Cassegrain antennas

The first approximation to the aperture efficiency of a paraboloidal reflector antenna is called the feed efficiency. The factorization of the feed efficiency into subefficiencies which account for losses due to spillover, cross polarization, nonuniform aperture illumination, and phase errors is considered. The relations between the radiation patterns of circularly and linearly polarized feeds are also derived.     

Aperture efficiency for paraboloidal reflectors

The definition and formulas for cross polarization, phase error, and illumination efficiency given by Ludwig and Thomas are shown to not always account for the correct cross polarization and phase error loss. New definitions and formulas are proposed that give a better separation of the losses associated with cross-polarized radiation, phase errors, and nonuniform aperture illumination.     

On the efficiency and radiation patterns of mismatched shaped Cassegrainian antenna systems

Calculations are carried out with regard to the aperture illumination efficiency, spillover efficiency, and blockage efficiency of a shaped Cassegrainian antenna system whose feed pattern is not similar to that for which the antenna was designed. It appears that a maximum overall efficiency may be expected for antenna systems with a feed pattern having a slightly narrower beamwidth than those for which the systems were originally designed. It is further proved that the radiation pattern of mismatched systems is very unfavorable in the case of the beamwidth of the feed pattern being wider than the beamwidth of the feed pattern for which the system was designed. This is due to overillumination of the edges.     

Radiation pattern synthesis for circular aperture horn antennas

A set of radiation pattern functions, suitable for synthesis of radiation patterns from circular aperture horn antennas, is obtained by assuming an aperture distribution consisting of the fields of cylindrical waveguide modes. A technique is presented for using a linear combination of the radiation pattern functions to approximate a desired radiation pattern. Linear combinations of the radiation pattern functions resulting in maximum secondary gain, when used to illuminate a paraboloidal antenna, are obtained empirically. Using spherical wave theory, maximum performance theoretically obtainable from an antenna is derived as a function of the aperture size of the feed system; the feed efficiency resulting from these theoretical limits on performance is compared to the feed efficiency of patterns obtainable from circular aperture horn antennas, and to experimental results of attempts to realize optimum circular aperture horn patterns.     

高斜效率高功率850nm氧化限制型垂直腔面发射激光器

报道了MOCVD生长的高性能850nm氧化限制型垂直腔面发射激光器.研制出的氧化直径为9μm的激光器25℃时的斜效率和阈值电流分别为0.82mW/mA和2.59mA,激光器在23mA时输出16mW最大光功率.氧化直径为5μm的激光器25℃时的最小阈值电流为570μA,其最大饱和光功率为5.5mW.     

Illumination,communication and energy efficiency analysis of indoor visible light communication systems under the influence of optical source emission characteristics

The effective illumination and data transmission capabilities of visible light communication (VLC) depend on the various emission characteristics of optical sources. The mathematical modeling and simulation of the indoor VLC over the illumination sources with different radiation patterns are presented in this paper. The performance analysis for the optical sources with Lambertian, Lambertian directional, Batwing and Gaussian radiation patterns is carried out in the aspects of illumination, communication and energy efficiency. The illumination analysis results that the Lambertian and Batwing sources can provide flat illuminance in communication plane than the other sources due to their greater illuminance uniformity. The communication ability of the diverse sources is analyzed with the distribution of optical power and RMS delay, and achievable data rate. The Lambertian and Batwing sources provide better user mobility as they have uniform optical power distribution, and they can provide 812 Mbps and 908 Mbps, respectively. The Lambertian directional and Gaussian sources have the optical power concentrated in some regions of indoor environment, and they can provide the 1.082 Gbps and 794 Mbps, respectively, in those regions. This makes these sources more suitable for the fixed VLC links. The energy efficiency of the Lambertian directional source is 108.2 Mbps/W, and its order of emission and directivity makes it more energy efficient than the other sources. The other source emission characteristics such as spectral power distribution curves and correlated color temperature are investigated. Based on all these analyses, the appropriateness and associated safety levels of optical sources in distinct VLC environments are proposed.

     

Power levels and packet lengths in random multiple access with multiple-packet reception capability

This paper extends our earlier results. We assume that the receiver has the capability of capturing multiple packets so long as the signal-to-interference-plus-noise ratio (SINR) of each packet is above a designed threshold T throughout its transmission period. We prove that, compared with a multiple-power-level system, the single-power-level system in which all nodes transmit at the maximum allowable power level achieves optimal throughput, under a condition that T exceeds the value 3.33. Given a minimum throughput requirement, under the same condition on T, the single-power-level system also achieves the maximum average packet capture probability as well as the optimum energy usage efficiency. If the multiple-power-level systems are constrained such that higher power levels always have shorter packet lengths, then the above results hold for T greater than 2.     

微波功率传输的理论研究

本文通过建立两口径天线传输效率的瑞利商式,对两口径天线的最大功率传输问题的求解作了系统、严格的讨论,给出了两圆口径天线的功率传输问题的解析解和相应的计算结果,为工程设计提供了理论依据。     

基于最大功率传输效率法的近场三维方向图赋形

讨论如何利用带约束的最大功率传输效率(CMMPTE)法通过阵列天线来综合三维方向图.通过引入测试接收阵列天线,待设计的阵列天线与之构成无线功率传输(WPT)系统,从而将方向图的综合问题转换成WPT系统功率传输效率(PTE)的优化问题.通过调整约束条件,在保证PTE最大化的条件下可获得阵列天线的激励分布,根据激励分布设计...     

Output coupling for closely confined Pb1-xSnxTe double-heterostructure lasers

The output coupling of an idealized, symmetric model of a double-heterostructure (DH) laser is analyzed theoretically using parameters suitable to Pb1-xSnxTe. For the TEOmode incident at the laser mirror and for thin optical guiding regions such that only the TEO, TE1, TMO, and TM1modes may propagate, an exact formulation of the coupling problem is obtained including mode coupling at the mirror into the continuum of unguided radiation modes. Using this formulation, the power reflection and transmission coefficients, the fraction of incident power coupled into the radiation modes, the mirror illumination, and the far-field pattern are calculated for typical parameters. Significant mode coupling can occur, limiting the maximum external efficiency of such lasers. This and other potentially undesirable characteristics resulting from close optical confinement, such as large output beam divergence, must be considered in design criteria for DH structures in this alloy system.     

谐振式电能无线传输系统中串串式模型研究

谐振耦合式电能无线传输系统利用磁场通过近场传输,具有辐射小、效率高、传输距离远且方向性强等特点。文中采用等效简化电路方法分析了谐振式电能无线传输系统串串模型的间距、工作频率、负载等参数对传输效率和功率的影响及内在关系,进一步推导出其计算模型。在间距和负载一定的条件下,通过Matlab仿真得到效率最优与功率最大时的工作频率相一致,输出功率对工作频率的变化敏感度更高这一规律。此外,设计了一套串串式结构的谐振式电能无线传输装置,通过实验验证了理论分析的正确性,为研究电能无线传输提供了参考。     

A six-junction GaAs laser power converter with different sizes of active aperture

We investigate a novel GaAs-based laser power converters (LPCs) grown by metal-organic chemical vapor deposition (MOCVD), which uses a single monolithic structure with six junctions connected by tunnel junctions to obtain a high output voltage. The LPCs with diameters of active aperture of 2 mm and 4 mm were fabricated and tested. The test results show that under an 808 nm laser, two LPCs both show an open circuit voltage of above 6.5 V. A maximum power conversion efficiency of 50.2% is obtained by 2 mm sample with laser power of 0.256 W, and an output electric power of 1.9 W with laser power of 4.85 W is obtained by 4 mm sample. The performances of the LPCs are deteriorated under illumination of high flux, and the 4 mm sample shows a higher laser power tolerance.     

高效率低旁瓣天线口面场分布函数研究

在赋形双反射面天线中,口面场分布函数对天线电气性能起到至关重要的作用。口面场分布函数妆接影响天线的增益和近角旁瓣。在传统卫星通信地面站中,要求天线第一旁瓣电平在-14dB以下,口面利用率在90%左右,而射电天文望远镜要求天线第一旁瓣电平小于-20dB,口面利用率要求在85%以上。研究并给出了一种整个口面能量均匀分布而外边缘低锥销的口面场分布函数,可以满足高增益,低旁瓣的要求。     

Multiple beam feed networks using an even number of beam ports

An aperture illumination compatible with the use of an even number of adjacent beam ports in a multiple beam feed network is discussed. The antenna pattern characteristics of near-in sidelobe levels, half-power beamwidth, aperture efficiency, and feed network loss are evaluated. Maximization of the available antenna gain at adjacent beam crossover points is shown to be possible for either sequential or simultaneons operation of a receiving system. The results presented indicate that lossy feed networks are quite suitable for certain array antenna applications.     

Propagation and radiation behavior of dielectric-loaded pluralhybrid mode multiflare conical horn antennas

A dielectric-loaded multiflare conical horn exhibiting the desirable features of low sidelobes and cross-polarization with the additional advantage of increased on-axis gain is reported. This new horn is developed by combining the techniques of multimode operation for low cross-polarization and sidelobe levels, and dielectric loading for aperture efficiency enhancement. The condition for the support of balanced hybrid modes for low cross polar radiation in the dielectric-loaded multimode horn is derived. Also, the equation for the dielectric thickness for maximum aperture efficiency at a given frequency is obtained. This new type of multimode horn is potentially simple to design, analyze, and manufacture, yet it exhibits the desirable features of a corrugated conical horn and hence can be an attractive alternative to corrugated conical horns for communication applications