我正在使用VNA和一对喇叭在X波段进行一些散射测量(RCS)。

一些参考文献表明，使用时间选通可以降低噪音。

还提到这可以通过使用软件(matlab)来处理测量数据来实现(S21)。

由于我们的VNA没有时域选项，我正在研究这种软件方法。

在阅读了应用笔记(http://cp.literature.agilent.com/litweb/pdf/5989-5723EN.pdf)和之前的几篇文章后，我的初步尝试是在有限带宽上使用Matlab的IFFT，测量S21

(比如8-14 GHz)，这很复杂。

我的理解是这与VNA的带通模式相对应。

我只对时域数据的大小感兴趣。

在之前的帖子“S21时域响应”，“https://community.keysight.com/message/4826#comment-4826”中，有一些关于带通模式的讨论。

_“在带通模式下，由于一些非显而易见的原因，IFT在分析上是不正确的。一个关键点是带通变换不假设埃尔米特响应，而是计算响应，就像所采用的数据是单面的一样

，“负”频率响应为零，而不是与具有相反符号的正相反。低通模式假设负频率响应具有相同的幅度和相反的相位，因此实际上产生负数据

在低通模式下执行此操作可确保纯粹的实际变换。在带通变换中，响应不是纯粹的实际，但实际上必须始终是复杂的。_ _带通响应通过频移数据计算得出

中心点在DC，计算IFT(复数形式，因为除特殊情况外，数据不是关于中心点的埃尔米特)，然后在时域中应用傅里叶变换理论将结果乘以e ^(jwt)其中

无线

s是“预移位”数据的中心频率。

因此，您将看到一个余弦(在实际上)和一个正弦(在虚构上)强加在低通响应上的数据(有时这也称为调制定理)._由e ^(jwt)调制是有意义的

。

既然只涉及时域中S21的大小，是否意味着可以放弃这个因素？

换句话说，简单地应用逆傅立叶变换将为我生成时域数据？

一个相关的问题是t0(开始时间)在哪里？

变换后的时域是否从t = 0开始？

我认为理论上时域数据是无限的和周期性的。

但是有可能找到t = 0或参考时间吗？

显然，这可以帮助识别来自物体的散射信号，因为发射器之间的距离是已知的。

谢谢！

以上来自于谷歌翻译以下为原文

I am doing some scattering measurement (RCS) in X band using VNA and a pair of horns. Some references suggest that using time gating can reduce noise. It was also mentioned that this can be achieved by using software (Matlab) to process the measured data (S21). Since our VNA does not have the time domain option, I am looking into this software method.

After reading the application note (http://cp.literature.agilent.com/litweb/pdf/5989-5723EN.pdf) and a few previous posts, my initial attempt is to use IFFT of Matlab on a finite bandwidth, measured S21 (say 8-14 GHz), which is complex. My understanding is that this is corresponding to the bandpass mode of VNA. And I am only interested in the magnitude of the time domain data.

In previous posts "S21 time domain response ", "https://community.keysight.com/message/4826#comment-4826 ", there are some discussions on the bandpass mode.

_"In bandpass mode, the IFT is not analytically correct, for some non-obvious reasons. One key point is that the band pass transform does not assume a hermitian response, but rather, computes the response as though the data taken is single sided, with the "negative" frequency response being zero, rather than identical to the positive with opposite sign. The Low Pass mode makes the assumption that the negative frequency response is of the same magnitude and opposite phase, so in effect, creates data at negative frequencies. Doing this in low pass mode assures a pure real transform. In the band pass transform, the response is not pure real, but in fact must always be complex._

_The band pass response is computed by frequency shifting the data such that the center point is at DC, computing the IFT (complex form, as the data is not hermitian about the center point except in special cases), then applying the Fourier shift theory in the time domain to multiply the result by e^(jwt) where w is the center frequency of the "pre-shifted" data. Thus, you will see a cosine (on the real) and a sine (on the imaginary) data imposed on the low pass response (sometime this is calLED the modulation theorem as well)._

The modulation by e^(jwt) makes sense. Now since only the magnitude of S21 in time domain is concerned, does it mean that this factor can be dropped? In other word, simply applying the inverse Fourier transform will generate the time domain data for me?

One related question is that where is the t0 (starting time)? Does the transformed time domain start at t=0s? I guess in theory the time domain data is infinite and periodic. But is it possible to locate the t=0, or reference time? Apparently this can help to identify the scattering signal from the object since the distance between the transmitter is known.

Thanks!

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