Statistically designed density-tapered arrays

The design of "thinned" planar array antennas is considered in which the density of elements located within the aperture is made proportional to the amplitude of the aperture illumination of a conventional "filled" array. Density tapering permits good sidelobe performance from arrays of equally radiating elements. The selection of the element locations is performed statistically by utilizing the amplitude taper as the probability density function for specifying the location of elements. The statistical design procedures and the theoretical prediction of performance are given. Application to a 50 wavelength diameter planar aperture is discussed and the results compared to conventional amplitude-taper designs. Examples of computed patterns are shown for density tapers modeled after 25, 30, 35, and 40 db circular Taylor distributions. The properties of a planar array of 10,000 elements are examined for "natural" thinning and for 70 per cent and 90 per cent of the elements removed. The sidelobes are determined more by the number of remaining elements than by the model amplitude taper. Statistically designed density-tapered arrays are useful when the number of elements is large and when it is not practical to employ an amplitude taper to achieve low sidelobes.     

基于CVT 排布的非周期栅格密度加权阵设计

相比传统周期栅格密度加权阵,非周期排布密度加权阵有很多优点,但对非周期排布密度加权阵的设计方法却不完善。该文提出了一种利用质心Voronoi 图设计密度加权阵的新方法,这种方法可以按照预期幅度加权设计非周期排布的密度加权阵,得到的单元排布具有非周期性和匀称性的特点。作为例子分析了一个直径为32.8 的圆形阵,分别计算了按圆口径泰勒分布25 dB, 30 dB, 35 dB 和40 dB 副瓣设计的阵列方向图。相比已有文献中的计算结果,用该方法能获得更好的副瓣性能和口面效率。      

Tapered beamforming for concentric ring arrays

In this paper, some conventional filtering windows are modified and applied to uniform concentric circular antenna arrays (UCCA) for spatial smoothing and sidelobe reduction. The modified windows are applied to individual rings of the array that will taper the corresponding current amplitudes. The resulted sidelobe level, beamwidth and stability for amplitude errors are discussed for the different proposed tapering windows where it shows a sidelobe reduction to about 49 dB as in the case of Binomial UCCA while the Hamming window shows the most immunity to tapered amplitude errors.     

基于遗传算法的相控阵天线口径激励的多阶振幅量化

本文利用二进制编码的遗传算法实现天线阵口径激励的振幅量化。该方法考虑了互耦的影响和大扫描角的情况,计算实例为98单元偶极子线阵,它安装在理想反射面上,单元距离反射面λ0／4,采用7阶振幅量化。在不扫描情况下可达到峰值副瓣-35dB,在60°扫描角情况下可达-30dB。     

Simplified Sidelobe Reduction Techniques for Concentric Ring Arrays

In this paper, a simplified sidelobe reduction technique for uniform concentric circular antenna arrays (UCCA) is proposed. This technique is based on modifying some conventional windows to control the amplitude feeding instead of using adaptive techniques which require excessive processing and calculations and suffer from the lack of practical application especially for UCCA. The modified windows are applied to individual rings of the array that will taper the corresponding current amplitudes. The resulted sidelobe level, beamwidth and stability for amplitude errors are discussed for the different proposed windows where it shows a sidelobe reduction to about 49 dB as in the case of Binomial UCCA while the Hamming window shows the most immunity to tapered amplitude errors.     

基于NLFM的超低旁瓣脉冲压缩方法研究

在新型的天气雷达中,由于地面杂波反射强度能达到30~55dB,为了测量雨水强度,要求旁瓣电平小于60dB。相对于线性调频信号通过幅度加权得到低旁瓣输出,非线性调频信号(NLFM)无需加权就可以得到很低的主副瓣比,因此没有加权引起的信噪比损失和主瓣展宽等问题。但是对非线性调频信号直接匹配滤波只能获得-40dB左右的主副瓣比,无法满足天气雷达实际应用的需要,因此文中提出一种基于非线性调频信号的改进设计方法,仿真结果表明,该方法可以有效降低旁瓣电平,获得-73dB的主副瓣比,但也会引入一定的信噪比(SNR)损失。     

Planar 64 element millimetre wave antenna

A simple 64 element planar array antenna, with H-plane sidelobes below -35 dB at larger angles than 19° from boresight and a gain above 30.4 dBi, is presented for the band 37.0-39.5 GHz. The radiating elements are fed in parallel by a waveguide feed network. The H-plane sidelobe level is reduced by using a combination of arrays, the zero in the element radiation pattern, and amplitude tapering     

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.     

一种空气同轴馈电的X波段低副瓣阵列天线

设计了一种应用于雷达系统中的低成本低副瓣阵列天线, 该天线阵包含256个辐射单元, 由四个64单元的子阵组成, 采用波导合成网络进行功率合成.天线单元采用空气同轴馈电的角锥喇叭, 空气同轴馈线内外导体呈方型结构, 其终端为短路馈电方式, 实现了内导体的自支撑设计和较低的传输损耗, 并依据综合幅度分布采用若干数量的不等功分器进行低副瓣设计.测试结果表明, 小于2的驻波带宽为0.5 GHz, 相对带宽为7.5%.另外, 中心频率的增益为30 dB, 增益大于29.5 dB的带宽为0.2 GHz, E面和H面的旁瓣电平为28.5 dB和29 dB.     

基片集成波导缝隙稀疏阵天线的设计

设计了一种应用于雷达系统中的低成本低副瓣阵列天线, 该天线阵包含256个辐射单元, 由四个64单元的子阵组成, 采用波导合成网络进行功率合成.天线单元采用空气同轴馈电的角锥喇叭, 空气同轴馈线内外导体呈方型结构, 其终端为短路馈电方式, 实现了内导体的自支撑设计和较低的传输损耗, 并依据综合幅度分布采用若干数量的不等功分器进行低副瓣设计.测试结果表明, 小于2的驻波带宽为0.5 GHz, 相对带宽为7.5%.另外, 中心频率的增益为30 dB, 增益大于29.5 dB的带宽为0.2 GHz, E面和H面的旁瓣电平为28.5 dB和29 dB.     

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 high-gain 58-GHz box-horn array antenna with suppressed gratinglobes

A low-profile high-gain antenna array of box horns for the frequency band 57.2-58.2 GHz is presented. The antenna consists of 256 radiating elements divided into two subgroups of 128 elements fed by a rectangular waveguide feed network. The radiating elements are fed in parallel and the waveguides are connected with T-junctions. The matching of the T-junctions is improved with a matching pin and a splitter. Because of the waveguide feed network, the element spacing is larger than one wavelength, which causes grating lobes. The grating lobes and sidelobes in the H-plane have been suppressed by the use of a combination of subarrays, a special characteristic of the box horn, and an array amplitude tapering. The measured sidelobe levels in the H-plane are below -30 dB at angles larger than 8° from boresight. A gain higher than 35.7 dBi and a return loss higher than 14.4 dB have been measured for the antenna over the band 57.2-58.2 GHz     

Ultra-low sidelobes from time-modulated arrays

Antenna patterns with ultra-low sidelobes have been obtained for an experimental receiving array designed with time-modulated slot radiators. The technique utilizes on-off RF switches which are programmed in a predetermined sequence to produce the desired pattern. The results of tests on an experimental eight-element slot array designed for sidelobe reduction are presented. Two examples are considered: 1) an initial static pattern with 30-db sidelobes which are reduced to about 40 db by sequential switching and 2) an initial static pattern with 13-db sidelobes which are reduced directly to about 40 db by a different sequence of switching. Measured patterns illustrating the sidelobe reduction are included. The applicability of the sidelobe reduction technique to large electronically steerable phased arrays is considered briefly and it is concluded that it is compatible with such systems.     

Designing Doppler signals to overcome transmission nonlinearities

Doppler processing requires a radiating signal with low spectral sidelobes over the range of frequencies at which Doppler shifts are expected. This is conventionally achieved by windowing the driving sine wave. The effectiveness of windowing depends upon the transmitter amplitude response, and is therefore affected by nonlinearity. This problem is overcome by gating the sine wave with a series of nonuniformly spaced pulses of constant duration and amplitude. The pulse start times then control the shape and level of the radiated spectrum; the most closely controlled sidelobes are those near the transmitted frequency. The resulting spectrum is not affected by nonzero threshold or limited linear range (typical sources of nonlinearity). Furthermore, amplitude shading (within the linear range) and pulse-duration variation can be introduced to control sidelobe levels at higher Doppler frequencies. Pulse-to-pulse phase shifts allow one to design a signal with a central spectral peak shifted from the perceived transmitted frequency     

An excellent reduction in sidelobe level for P4 code by using of a new pulse compression scheme

P4 polyphase code is well known in pulse compression technique. For P4 code with length 1000, peak sidelobe level (PSL) and integrated sidelobe level (ISL) are ?36dB and ?16dB, respectively. In order to increase the performance, there are different reduction techniques to reduce the sidelobes of P4 code. This paper presents a novel sidelobe reduction technique that reduces the PSL and ISL to ?127dB and ?104dB, respectively. Also, other sidelobe reduction techniques such as Woo filter are investigated and compared with the novel proposed technique. Simulations and results show that the proposed technique produces a better peak side lobe ratio (PSL) and integrated side lobe ratio (ISL) than other techniques.     

天线副瓣对雷达探测的影响研究

雷达天线均有副瓣,而且覆盖主瓣以外的所有区域。为了分析天线副瓣辐射对雷达探测的影响,建立了副瓣辐射、副瓣接收模型,给出了副瓣损耗因子、杂波增强因子与天线主瓣零点宽度、平均副瓣电平的关系公式。理论分析和计算表明,天线副瓣对雷达最大探测距离有一定的影响,对副瓣自卫距离有较大的影响,对杂波的影响很小。当天线副瓣较低时（平均副瓣电平优于-30 dB）,副瓣损耗因子对最大探测距离的影响可忽略不计;当天线副瓣较高时（平均副瓣电平-27～-20 dB）,副瓣损耗因子对最大探测距离的影响应予考虑。     

Using continuous aperture illuminations discretely

An iterative procedure is described for fitting a continuous aperture illumination function to a small discrete element array such that the far-field antenna pattern has prescribed sidelobe behavior. Control of successive sidelobe levels in the array factor pattern is used to minimize an error expression comprised of the sum of the squares of the differences between calculated and specified levels for a selected number of sidelobes. The coefficients of a finite series defining the continuous aperture illumination are the variables employed in a Newton-Raphson solution. A sum beam aperture excitation for meeting the 20/30 dB sidelobe requirements of the 1973 OTP manual is derived for a small array and shown to be a useful approximation for a larger array situations. The procedure has been extended to difference beam illumination functions. Extensions to other aperture illuminations are indicated.     

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.     

On a simple method of obtaining sidelobe reduction over a wideangular range in one and two dimensions

A patented technique for suppressing the sidelobes of an array antenna is considered. This technique involves the addition of two elements, one at each end of the array, which together produce an interferometer pattern used for the cancellation of sidelobes. It is shown here that the technique is most effective for uniform illumination and that there then exists an optimum fixed position for the added elements. The amplitude of the excitation of the auxiliary elements determines the angular location of the region of sidelobe reduction while the phase of the excitation tracks the beamsteering phase of the array. Thus, this technique is seen to be easily implemented in an array controlled by coupled oscillators. The technique generalizes in a straightforward manner to two-dimensional (2-D) arrays in which case a set of auxiliary elements on the perimeter of the array is required. A 2-D oscillator controlled array of this type is described here with which one can produce a main beam and a sidelobe suppression region that can be independently positioned anywhere in a hemisphere provided they do not coincide     

The peak sidelobe of the phased array having randomly located elements

A formula is derived for the peak sidelobe level of a phased array in which the elements are randomly located. The parameters of the formula are the number and size of the array elements, size of the array, wavelength, beamsteering angle, and signal bandwidth. The theory is tested by measurement of the peak sidelobe of several hundred computer-simulated random arrays. Unlike the case for the conventional array the effect of spatial taper (nonuniform density of element location) upon the peak sidelobe level is minor. The peak sidelobe of the two-dimensional planar array is approximately 3 dB higher than that of the linear array of the same length and same number of elements.