A parabolic reflector with asymmetric low sidelobes

A technique for generating low sidelobes on one side of the main lobe for a parabolic reflector antenna is presented. The reflector system that generates such an asymmetric sidelobe pattern consists of a central parabola with two sections of offset parabolas situated at the top and bottom of the central parabola. By adjusting the positions and dimensions of the side reflectors, considerable suppression of the first few sidelobes can be obtained. Further, by similar adjustments it is possible to achieve suppression of sidelobes on both sides of the main beam, though this suppression is relatively less. The technique, though explained in detail with reference to a cylindrical geometry, is extended for a paraboloid of revolution. The analysis program utilized for the optimization of the side reflectors is based on physical optics current integration.     

An offset reflector antenna with low sidelobes

The corrugated conical horn is considered to be an ideal feed for low sidelobe reflector antennas because of its unique characteristics. Analysis is carried out to show that low flare horns are preferred over high flare horns to give rise to low sidelobe performance for a given offset reflector antenna system.     

On-board K-band multibeam antenna configuration with low sidelobes and low crosspolarisation

On-board antennas of 2.5/3.5 m in diameter which cover Japan with 13 beams in 30/20 GHz bands are developed. To achieve intense frequency reuse, a 9-horn cluster feed is adopted. A tower mounted type deployable antenna configuration is selected so as to overcome the fairing envelope limitation     

A novel linear and planar multiband fractal-shaped antenna arrays with low sidelobes

Fractal antenna arrays are usually used to tune multiband frequencies. However, these types of iteratively constructed antennas are associated with undesirable high sidelobe levels and low directivities. In this paper, an optimization procedure based on the genetic algorithm is used to find the optimal weights of the array elements such that the corresponding array patterns have low sidelobe levels and good directivity. Moreover, the fractal nature in the proposed arrays is maintained regardless of the optimized weights. Thus, the proposed fractal-shaped array maintains its capability in performing multiband frequency operation. These good radiation features make the proposed fractal-shaped array more appropriate for the current and future wireless communication applications. Simulation results confirm the superiority of the presented linear and planar fractal-shaped array structures with compared to the conventional fractal cantor linear array and the standard Sierpinski carpet planar array. For the proposed fractal cantor linear array, the sidelobe level has been reduced to more than −20 dB at different operating frequencies, and the directivity has been improved by more than 8 dB, while the modified Sierpinski carpet planar array has achieved −30 dB depressions in the sidelobe level and 6 dB improvement in the directivity.     

Pulse compression with very low sidelobes in an airborne rainmapping radar

Pulse compression allows a substantial reduction in the peak transmitted power of a radar and is attractive for spaceborne remote sensing applications. In the case of a downward looking rain measuring radar, however, the range sidelobes associated with surface return can mask return from rain and must be kept to a minimum. The authors describe the pulse compression system for the NASA/JPL Airborne Rain Mapping Radar. This system uses time-domain weighting of the transmitted pulse and is able to achieve a range sidelobe level of -55 dB or better in flight tests. This is significantly lower than other values reported in the open literature     

A small dipole-fed resonant reflector antenna with high efficiency, low cross polarization, and low sidelobes

The computer-aided optimization of a small five-wavelength diameter reflector antenna with a center-supported dipole-disk feed is described. The primary radiation is controlled by using a patented beamforming ring to give low cross polarization and low sidelobes due to spillover. The efficiency is maximized by controlling and taking advantage of the multiple reflections between the feed and the reflector. This has inspired the name "resonant reflector antenna." The gain from the feed reflector resonances is so large that it compensates almost completely for the about 1 dB loss due to center blockage of the aperture.     

Conformal four-beam antenna arrays with reduced sidelobes

Investigations on sidelobe reduction in multibeam conformal antenna arrays are presented. The recently presented concept of sidelobe reduction in planar multibeam antenna arrays in conjunction with the phase compensation technique has been applied for the design of reduced sidelobe multibeam conformal antenna arrays. Six- and eight-element antenna arrays fed by modified Butler matrices have been investigated and minimum radii have been found for which the sidelobe level is comparable to the respective planar multibeam arrays. A novel fully integrated six-element four-beam antenna array has been successfully designed in which sidelobes equal -14 dB for all four beams have been achieved.     

A very low noise preamplifier for extremely low frequency magnetic antenna Feng Shimin(冯士民), Zhou Suihua(周穗华), and Chen Zhiyi(陈志毅)

Besides the electrode-pair antenna,the magnetic antenna is also used for the extremely low frequency （ELF） submarine communication.To receive the weak ELF signals,the structure of a small sized magnetic antenna determines its specific electrical characteristics.The ELF magnetic antenna shows high internal resistance, alternating-current impedance,and a resonance frequency near the operating bandwidth.In accordance with the electrical characteristics of ELF magnetic antenna,a low noise preamplifier and frequency compensation circuit were designed and realized.The preamplifier is a three-stage negative feedback circuit,which is composed of parallel JFET,common-emitter amplifier with a Darlington structure and a common-collector amplifier in push-pull connection.And a frequency compensation circuit is cascaded to compensate the characteristic in low frequency range.In the operating bandwidth f = 30-200 Hz,the circuit has a gain of 39.4 dB.The equivalent input noise is 1.97 nV/Hz^1/2 and the frequency response keeps flat in operating bandwidth.The proposed preamplifier of the ELF magnetic antenna performs well in receiving ELF signals.     

Broad-band flared horn with low sidelobes

A circular horn antenna flared like a trumpet has been analyzed with the geometrical theory of diffraction and tested experimentally. Sidelobes are extremely low (-75 dB) and agree with theory. Low sidelobe performance is predicted to be broad-band and to improve with higher frequencies. The full aperture of the tested horn is about50 lambda. Suggestions are made for even better low sidelobe antennas.     

A one-parameter circular aperture distribution with narrow beamwidth and low sidelobes

A one-parameter circular aperture distribution is developed which provides an optimum compromise between narrow beamwidth, low sidelobes, and low apertureQ. The pattern is a modifiedJ_{1}(x)/x, analogous to the Taylor one-parameter modified sin(x)/xline source distribution. Sidelobe envelope taper is essentially that of a uniformly excited circular aperture; hence the aperture is lowQ. The aperture distribution which is rotationally symmetric is given by a modified Bessel function of zero order. Like all high efficiency distributions, it has a pedestal. All antenna quantities, sidelobe ratio, beamwidth, aperture efficiency, and edge taper, are uniquely related to the parameterH. A table of these quantities is given for sidelobe ratios up to 50 dB. A typical pattern and several distributions are graphed. This new distribution allows tradeoff studies to be made against any design quantity, with all other quantities determined through the one-parameter.     

An investigation of concentric ring antennas with low sidelobes

An analysis is made of circular antenna arrays with diameters being 2 to9lambda(the minimum inner circle diameter being0.4lambda) containing 3 to 18 concentric circles. For the purpose of computation of the array factor the elements of the array are assumed to be isotropic radiators. The elements of each circle have equal current amplitudes and are phased so that the contributions of all the elements add in phase in the direction of the main beam. The Chebyshev radiation pattern function is approximated by a truncated Fourier-Bessel series, from which the current amplitude of each circle is obtained. From these current amplitudes a method for computing the current amplitude to excite a new distribution of fewer circles is shown. Also, an empirical method is given for improving the sidelobe level of the radiation pattern by adding an element to the center of the array. A number of circles in the array sufficient to avoid pattern deterioration is found to be the integer nearest to5d/4lambdafor -20 and -30 dB sidelobe level and4d/3lambdafor -40 dB, wheredis the diameter of the array. This represents a large reduction in the number of circles needed over the Fourier-Bessel series representation in the case of large antennas. Experimental verification of the computed pattern is made for an array of two concentric circles with diameters of0.8lambdaand1.6at a frequency of 90 Mc/s. The elements of the array were vertical monopoles.     

Surface clutter due to antenna sidelobes for spaceborne atmosphericradar

A spaceborne radar for atmospheric observation must be able to detect atmospheric backscatter in the presence of clutter from the surface, due to antenna sidelobes. Such clutter can come from the same pulse as that observing the atmosphere if the radar antenna is pointed off-nadir. However pulses both prior and subsequent to the pulse observing the atmosphere can also contribute to clutter, and surface clutter can be a problem even for nadir-looking radars. Here, the problem is analyzed by deriving a method for computing clutter which includes effects of all contributing transmit pulses, Doppler shifting, finite receiver bandwidth, and curved Earth's surface. The results are applied to analysis of existing radars and design of future radar systems     

A monopolar patch antenna with very wide impedance bandwidth

A monopolar patch antenna that utilizes a bandwidth broadening technique is investigated experimentally and numerically. The proposed antenna consists of a monopole that is formed by connecting four trapezoidal plates orthogonally. A circular patch, which is shorted to the circular ground plane by four shorting wires, is placed at the top of the monopole. The antenna possesses 10-and 14-dB return loss bandwidths of 138% and 107.2% respectively, which is about 49 times that of the corresponding monopolar wire-patch antenna. Also, it provides monopole-like radiation patterns over such wide operating bandwidth. As the proposed antenna can achieve such wide impedance bandwidth with relatively low profile, it is very suitable for multi-band mobile communication systems.     

Uniform complex codes with low autocorrelation sidelobes (Corresp.)

The problem of designing uniform-amplitude codes with good autocorrelation functions can be regarded as a problem of mlnimizing a function of several continuous variables. The application of numerical methods of minimization is shown to yield codes with lower sidelobe levels than other known codes of equal lengths. Codes with no sidelobe exceeding unity have been found for lengths as large as 18.     

Compact multimode horn with low sidelobes for global Earth coverage

A new multimode corrugated horn is described for full-Earth coverage from a geostationary satellite. The horn has low sidelobes, low cross polarization, and is compact. We outline the design of this horn and compare its performance with other circular horn types, including conventional single and multimode-corrugated horns and dielectric loaded horns. A design was fabricated and measured results are described for return loss, radiation patterns, and axial ratio. These measurements demonstrate excellent agreement with computer predictions using mode-matching software     

月基甚低频射电干涉仪Tripole天线特性研究

对月基甚低频射电干涉仪所用Tripole矢量有源天线进行理论分析,计算了不同激励下的辐射方向图以及给定方向图时所需的激励。不同于传统的天线阵列方法,单一的Tri-pole(三阵子)天线即可实现对入射波达波方向(DOA)的估计。运用改进的基于单位矩阵束(UMP)和最小二乘法(LS)的算法实现了对Tripole天线达波方向的估计,该算法适用于对入射波不同频率分量的DOA估计,计算量小,且估计精度更高,仿真结果表明了算法的有效性。     

A synthesis of array antennas for high directivity and low sidelobes

By application of a Gegenbauer polynomial, pattern synthesis of array antennas which have high directivity and low sidelobe level is investigated. A Chebyshev or uniform-amplitude array is included as a special case of the result obtained. The current amplitudes of the array elements are represented by a Jacobi polynomial and are easily calculated. It is shown by numerical calculations for a linear array and a hexagonal planar array that there is an optimum directivity for a specified sidelobe level within a class of Gegenbauer-polynomial patterns.     

Effect of field amplitude taper on measured antenna gain and sidelobes

Amplitude taper of the field of a pattern measurement range produces gain and sidelobe values lower than the true values. A calculation is made using one-parameter distributions, for which the gain can be found in closed form, thereby avoiding the errors in previous calculations. For small tapers both gain errors and sidelobe level errors are linearly proportional to taper (dB). These results are useful in the design of pattern ranges, especially for very low sidelobe antennas, where the amplitude taper is more critical.     

A curved spiral antenna above a conducting cylinder

A curved spiral antenna above a finite hollow conducting cylinder is analyzed using the method of moments. The effects of cylinder length 2H and cylinder radius r_cy on the radiation characteristics of the spiral are evaluated. As 2H increases, the cross-polarization component of the radiation field in the broadside direction decreases to a constant value (approximately -18 dB). When 2H is greater than one wavelength (λ₀), the input impedance of the spiral above a cylinder of radius r_cy=0.25 λ₀ is almost constant (250-j20 Ω) with a gain of approximately 7 dB. The spiral above a cylinder of (2H, r_cy)=(2.7 λ₀, 0.25 λ₀) shows a 3-dB axial ratio bandwidth of approximately 23%, which is wider than a flat spiral antenna above a flat ground plane of infinite extent     

基于副瓣峰值控制的天线阵方向图综合

在干扰入射方向,自适应天线阵方向图会产生零陷,使副瓣电平降低。根据自适应阵列的这一特性,应用一种基于最大输出信噪比准则的改进自适应算法对天线阵进行方向图综合。假定有大量干扰信号施加到方向图副瓣区,通过只对副瓣峰值电平进行控制调整加权值,降低副瓣电平,得到满足副瓣要求的目标方向图,使算法得到简化。可以应用于不等间距直线阵列和矩形平面阵的方向图综合问题。考虑了阵元间的互耦及阵元方向图特性的影响。仿真结果证实了该算法是可行的。