Front-to-back ratio of paraboloidal reflectors

An analysis is presented which uses the uniform geometrical theory of diffraction for determining the near fields diffracted by a paraboloid either with or without a conical flange attached to its circular rim when an axially propagated plane wave is incident on the concave or convex portion of the paraboloidal reflector. The field correlation theorem is used to determine the power coupled by a prime focus feed associated with the paraboloid which is being illuminated by a uniform plane wave. Based on this analysis, the front-to-back ratio of unflanged and flanged paraboloids is computed. Computed results show satisfactory agreement with the available measured as well as computed results based on alternative procedures. The variation in the on-axis gain on a prime-focus reflector when the feed is displaced from the focus is studied. Typical computed results are presented and compared with the available measured data. Computed results on the front-to-back ratio of paraboloids (flanged or unflanged) illuminated by a PFF whose radiated field exhibits phase variation over a constant radius are also presented     

The physical optics of focused scatterers using source multipole expansions

A multipole-expansion technique is developed which permits the two-dimensional scattering integral for reflector antennas to be replaced by a finite sum of simple algebraic terms. The series, which accurately represents the radiated field over the main antenna beam and first few sidelobes, converges rapidly because the source dimensions are small. It is demonstrated that the reciprocity theorem is satisfied by the boresight physical-optics field of a paraboloid illuminated by a generalized linear electric current feed centered at the focus.     

Beam squint in a linearly polarised offset reflector antenna

A beam squint has been found to occur in the field radiated by an offset paraboloid antenna illuminated by a feed with linear polarisation in the plane of offset. The squint, whose existence has been confirmed by computed and measured radiation patterns, occurs in the offset plane, and is typically 0.03 of a beamwidth for a reflector of 6-wavelengths diameter. An assessment is given of the likely effect of the squint on the performance of an offset reflector radiating a circularly polarised field     

Selection of the microwave-beam parameters in a wireless system for energy transportation from a space electric power station to the Earth

An algorithm for finding the parameters of the microwave beam used for power transportation from a space electric power station to the Earth is considered. It is shown that, for specified geometries of antenna and rectenna systems, it is possible to increase the received power if the density of the radiated power at the antenna center and the truncation parameter of the Gaussian field distribution are simultaneously increased. It is found that, in this case, the transmission efficiency decreases only slightly as compared to the case of optimum transmission.     

A High Efficiency Launcher and Mirror System for Use in a 110 GHZ TE<Subscript>22,6</Subscript> Mode Gyrotron

A four-mirror internal quasi-optical mode converter designed for a CPI gyrotron is discussed. Many improved methods were used in designing the mode converter. The launcher was designed and analyzed using the TOL and Surf3d codes developed by CCR. Mirrors 1 and 2 were designed using analytic surfaces to shape the general wavefront curvature of the beam radiated from the launcher. Mirrors 3 and 4 were iteratively designed using improved techniques that produced smooth mirror surfaces. Good agreement was found between theory and low-power cold-test measurements. The fraction of power coupled between the target Gaussian beam and the output of mirror 4, inferred from measurements, was 0.990. The stray radiation from the internal quasi-optical mode converter, inferred from measurements, was only 1.9% of the total power radiated from the launcher. This resulted in a high overall system efficiency of 97.0%, which is greater than previous designs.     

Directivity of planar array feeds for satellite reflector applications

Array-fed reflector antennas are used extensively in today's contour and multiple beam satellite antennas. To determine the directivity of these antennas theoretically, the total radiated power of the array feed must be accurately computed. In this paper, a closed-form expression for the radiated power is obtained for arrays with the well-known(cos theta)q-type element patterns. The formulation is general, and takes into account polarization, nonsymmetricE- andH-plane element patterns, nonuniform element spacings and arbitrary complex excitation coefficients. Selective numerical data are presented to demonstrate the usefulness of this result. Comparisons are made with the available results obtained using direct numerical integration techniques, and with other available data based on less general formulations. Excellent agreement is observed for all cases. In particular, data are presented on the directivity of seven-element cluster feeds used in multiple beam designs, and an array feed for producing a contour beam covering the United States Eastern Time Zone (ETZ).     

Factors Involved in Gain Determination of A Tv Antenna

Gain is a vital characteristic of a broadcast TV antenna because of the direct relationship of antenna gain to the station's maximum effective radiated power, or ERP. This paper discusses the various parameters that may influence antenna gain, such as beam tilt, null fill and feed system efficiency. These and certain other factors must be taken into consideration in predicting the gain of a proposed antenna, whether it be horizontally or circularly polarized. Although a conservative value of the gain is estimated, the procedure will assure that the specified gain is achieved.     

Intermodulation in multiple fixed beam distributed amplifier phased array antenna systems

In the recent development of phased array/distributed amplifier systems for application to mobile satellite or thin route communication systems, the intermodulation (IM) generated by the element amplifiers is spatially dispersed in such a way that some of the IM radiated energy falls outside the intended beam area. In addition, some of the IM falling inside the beam area has frequencies different from the carriers intended for that area. It is known that for fixed beam systems with frequency reuse, an average IM noise reduction of several dB can be realized. In the specific case under investigation, of four beams, nine frequencies and 12 carriers (1-33 frequency reuse factor), an IM improvement of about 2-0 dB is realized. The improvement in carrier-to-IM-noise ratio can be applied to increase system capacity, or for given capacity it can be used to reduce RF power amplifier back-off, which can be translated into a reduction of spacecraft prime power requirement. The considerable advantage gained from the multiple beam distributed amplifier approach makes it worthwhile to explore the workings of such a system and other benefits it may offer. One of the benefits is a common RF power pool for all carriers and beams, and the other is the spatial dispersion of intermodulation (IM). A satellite multiple beam pattern and the spatial dispersion of IM products are shown in Figure 1.     

Aperture matching for an infinite circular polarized array of rectangular waveguides

This paper studies the polarization of the main beam radiated from an infinite array of rectangular waveguides, and in particular, illustrates the matching procedure for the design of a circularly polarized array. It is demonstrated that the use of resonant irises at the waveguide openings together with a conventional matching junction inside the waveguides can improve both the power and the axial ratio of the main beam in a circularly polarized array. In general, a good matching design is the one which gives a proper compromise between the power and the polarization, and is not necessarily the one minimizing the reflection.     

Active feedback microstrip leaky wave antenna-synthesiser designwith suppressed back lobe radiation

The design of an active leaky-wave antenna which integrates the antenna with a feedback synthesizer is introduced. The measurement result shows that the antenna has very low back lobe radiation compared with that of traditional single-terminal feeding leaky-wave antennas. Single frequency measurement shows that the radiated power difference between the main beam and back lobe is >15 dB at 8.2 GHz. For the designed feedback synthesizer antenna, the measured radiated power difference between the main beam and back lobe is >15 dB at 9.25 GHz, and the scanning angle is ~5° as the synthesizer frequency sweeps from 9.25 to 9.37 GHz     

Large signal behavior of high power traveling-wave amplifiers

The results of an experimental investigation on the large signal behavior of a kilowatt power level helix type traveling-wave amplifier tube are presented. Operation with and without attenuators was investigated using a movable electromagnetic probe to measure power level along the tube. Quite different effects of drive power and beam voltage on the saturation level were found for operation with and without attenuators. The maximum power level is lower for attenuator operation. Also, power levels do not continue to increase with increasing beam voltage and drive power. In contrast, attenuator-less operation produces the highest efficiency, and the power levels continue to rise with increasing beam voltage and drive power. Conversion efficiencies as high as 25 per cent are obtained with an attenuator and as high as 40 per cent without an attenuator. Efficiency calculations based on small-signal theory can be made to agree reasonably well with the experimental attenuator-less operation efficiencies by assuming an appropriate ratio of the ac component of beam current to the dc component of beam current, i/I0.     

High-performance 980-nm ridge waveguide lasers with a nearly circular beam

We report high-performance 980-nm ridge waveguide quantum-well lasers with extremely low vertical beam divergence of 13/spl deg/. A very small aspect ratio of 1.6 is obtained at high operating power of 900 mW. In addition to the more circular beam, low threshold, high efficiency, high characteristic temperature, and high output power of over 1.18 W are achieved. The fiber coupled output power can be as high as 680 mW with fiber Bragg grating stabilization. Excellent wavelength and power stability are also demonstrated.     

Design and Simulation of a Wide-Beam High-Power Parabolic Antenna with Dual-Source

For resolving the essential problem that the beam is too narrow in the application of the high-power UWB (Ultra-Wideband) antenna with single-source, a novel wide-beam high-power parabolic antenna with dual-source has been designed, and the edge of the paraboloid was cut in order to reduce the size of the antenna. Radiation properties of this proposed antenna are studied with finite-difference time-domain (FDTD) numerical method. The radiation properties of the proposed antenna can be improved by changing the structure of the parabolic antenna and adjusting the angle between the source and the axis of the antenna. The result shows that the beam-width has been improved significantly under the precondition of maintaining the peak power, and also the size of the antenna was minished by cutting the edge of the paraboloid.     

CO_2激光治疗慢性颗粒性咽炎的研究

目的 :评价CO2 激光束对慢性颗粒性咽炎治疗的有效性和适用性。方法 :应用功率密度 (辐照度或剂量率 )大约为 1 0 7W /m2 的CO2 激光束。在 5年时间里 (1 995～ 2 0 0 0 )对 642名慢性颗粒性咽炎患者在门诊进行点射治疗和随访一年 ,结合他人已报道的工作深入分析了CO2 激光束治疗咽炎的光学与医学理论基础。结果 :临床显示CO2 激光治疗慢性颗粒性咽炎十分有效 ,痊愈率高达 81 2 % ,总有效率在 98 8%以上。结论 :确认使用小型便携式CO2 激光器治疗慢性颗粒性咽炎简单、快速、经济、有效、实用。     

Beamsteering for Non-uniform Weighted Array-Fed Reflector Antenna

In this paper, a beamsteering scheme for an array-fed paraboloid reflector antenna is proposed. In this method, a non-uniform amplitude weighting strategy is used in order to demonstrate an offset fed for the reflector antenna. Steered beam is kept in shape in terms of half power beam width (HPBW) and relative side lobe level (RSLL). To do so, an analytical derivation of beam pattern is performed for the array-fed reflector antenna. Two standard non-uniform weighting techniques, Binomial and Dolf-Tschebyscheff, are employed for this reason. Finally, a multi-object optimization method is proposed to provide the best weighting. The computer simulations are performed for different multi-object optimization scenarios. The results reveal an improvement beam shape in terms of HPBW and RSLL traditional non-uniform weighing methods.

     

时域天线阵列半功率波束宽度计算

对于冲击雷达系统中的时域天线阵列,提出点源近似模型,用来计算时域超宽带天线阵列辐射瞬态电磁脉冲的场方向图以及辐射波束的半功率波束宽度。采用点源近似模型计算的半功率波束宽度和CST仿真结果一致,并和实验测试结果吻合得很好。实验表明,阵列辐射瞬态电磁脉冲具有波束聚焦特性,点源近似模型可以作为一种简便的方法,对时域天线阵列的参数进行分析。     

Multirod resonators for high-power solid-state lasers with improvedbeam quality

Many laser applications require high beam quality at high output power and a broad variation of the output power. The ratio of power variation ΔP_out to beam parameter product &thetas;_m-w_m for a single rod inside a stable resonator is a constant which depends on the intrinsic crystal parameters and the slope efficiency only. A broad range of the output power causes a large beam parameter product, i.e. a low beam quality. By using several rods inside the same resonator and by a suitable choice of rod position and resonator parameters, the output power range can be increased without reducing the beam quality. In the same way, the beam quality can be improved without reducing the output power. The details of multirod systems are discussed and compared to experimental results     

Shielding Measurements of Equipment Enclosures in the Radiating Near Field

To evaluate the shielding performance of an equipment-level enclosure, a new measure termed shielding power ratio is proposed, which includes the average shielding power ratio (AS) and a statistically based enhancement factor. Two measurement environments, the anechoic chamber and the reverberation chamber, are considered and compared. To achieve a quick estimate of such measure, the reverberation chamber is proposed to measure the AS. The enhancement factor can be derived from the statistical analysis on both measurement results and simulation results. Based on the enhancement factor and the total radiated power, the maximum power density radiated from the enclosure can be estimated accurately. The paper is informing new developments in IEEE Standard 299.     

Ideal efficiency of a radiating element in an infinite array

The efficiency of a radiating element in an infinite planar array has been defined as the ratio of the power radiated to the power available from the element. This efficiency is a measure of the strength of mutual coupling effects and also of the average reflection coefficient magnitude at a typical element in the active array as the elements are phased over a prescribed range. An upper bound to this efficiency, which is only a function of the array geometry, exists and corresponds to an array of antennas with certain ideal characteristics. A technique for evaluating this ideal or maximum efficiency of an element in an arbitrary infinite lattice is presented. While this efficiency is readily evaluated for some special configurations, the computation for any general space lattice becomes straightforward in terms of the formalism. The formalism is based on the "reciprocal lattice" and a transformed (Cartesian) version of the space and reciprocal lattices. The required integral is numerically equal to the area common to a unit square and an ellipse in this transformed lattice. Results are given for various rhombic and parallelogram lattices which include the square and the equilateral triangle as special cases. It is noted that for parallelograms of aspect ratio greater than about 4 to 1, the efficiency is nearly the same as for the limiting linear array.     

一种辐射功率检测器的研制

设计实现了一种便携式、通用性强、模块化,高可靠性的辐射功率检测器。该检测器在有源电子对抗设备的日常维护、保养中,可用于辐射功率的快速准确检测,可适应于不同频段、不同环境的应用需要,提高了有源电子对抗设备的维护检测效率,解决了有源电子对抗设备日常维护难以检测的难题。