为什么天线都有旁瓣？（sidelobe）

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天线单元间距太远

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深层次的原因我想是由于干涉引起的

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场到达某处的相位不同 所以引起的叠加不同 从而产生了主瓣和旁瓣

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楼上所说即是干涉的最基本原理  其实微波和光的干涉原理是一样的 而光的干涉可以看到明暗相间的条纹，天线的波瓣反映则是电磁波的干涉效果（不知道理解是否正确还请各位指教）

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又查了一些资料， 
是这样解释的： 
天线上的电流分布的傅立叶变换就是天线的pattern 
如果电流是高斯分布的话那么天线的pattern 就是高斯的，没有旁瓣， 
如果电流是其他的分布，那么大部分的傅立叶变换都会有旁瓣。 
 
我学习了傅立叶变换的性质，还是不理解这一点，难道有这样的性质：有限面积（截断）的电流分布对应 傅立叶变换的旁瓣？ 
等待高人指导， 
谢谢拉！

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我查的资料是wiki百科全书上的解释，大家可以参考一下。 
 
还有一种不会出现旁瓣的可能就是，天线尺寸特别小，比如特别小的dipole（极子天线）或是其他的小的天线单元等等出来的场就没有旁瓣的 
 
（为什么小的不出现旁瓣呢？还是不明白呀？等待大家的讨论） 
 

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方便大家讨论，把原文copy过来了，和干涉有关系。 
 
The nulls between sidelobes occur when the radiation patterns passes through the origin in the complex plane. Hence, adjacent sidelobes are generally 180° out of phase to each other. 
 
Because an antenna's far field radiation pattern is a Fourier Transform of its aperture distribution, most antennas will generally have sidelobes, unless the aperture distribution is a Gaussian, or if the antenna is so small, as to have no sidelobes in the visible space. Larger antennas have narrower main beams, as well as narrower sidelobes. Hence, larger antennas have more sidelobes in the visible space (as the antenna size is increased, sidelobes move from the evanescent space to the visible space). 
A typical radiation pattern of phased arrays whose inter-element spacing is greater than half a wavelength, hence the radiation pattern has grating lobes. 
 
For discrete aperture antennas (such as phased arrays) in which the element spacing is much greater than a half wavelength, the aliasing effect causes some sidelobes to become substantially larger in amplitude, and approaching the level of the main lobe; these are called grating lobes, and they are identical, or nearly identical in the example shown, copies of the main beams. Grating lobes are a special case of a sidelobe. In such a case, the sidelobes should be considered all the lobes lying between the main lobe and the first grating lobe, or between grating lobes. It is conceptually useful to distinguish between sidelobes and grating lobes because grating lobes have larger amplitudes than most, if not all, of the other side lobes. 
 
For antennas used as receivers, sidelobes make the antenna more vulnerable to noise from nuisance signals coming far away from the transmit source. For transmit antennas communicating classified information, sidelobes represent security vulnerability, as an unintended receiver may pick up the classified communication.

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有人理解这段英文的第二段话吗？

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电流分布的数学表达，再经傅里叶变换后的结果，并不是所有天线都有副瓣，全看天线或阵面的电流分布

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