怎么使用IFFT（matlab）将频域转换为时域

在诸如您的特殊情况下，您可以考虑在VNA上使用选项010（如果它是Agilent或HP VNA），以允许分析仪为您计算变换。
使用的方法是专有的，但经过多年的审查，往往提供良好的结果。



     以下为原文

  In unusual cases such as yours, you might consider using option 010 on the VNA (if it is an Agilent or HP VNA) to allow the analyzer to compute the transforms for you.  The methods used are proprietary, but have been fully vetted for years, and tend to provide good result.

如果你想要一个免费的解决方案，你可能想以非常低的成本查看软件VNWA https://www.sdr-kits.net/你可以免费下载该软件并加载.s2p文件并显示
时域数据。
当然选项010更好，但它并不便宜。
如果VNA陈旧且过时，请询问HP / Agilent Yahoo团队，如果幸运的话，某人可能会给你一个代码来启用选项010.事实上，Alltest的某人在那里写了他们会添加$ 300- $ 400的选项
，但有一对夫妇愿意在非常古老的乐器上无所作为。
如果您在X波段工作，这意味着您没有使用8753，可以获取启用该选项的代码。
我知道Techmaster Electronics是在8720D上完成的，因为我的VNA在校准证书上说添加了选项010。
我认为对于PNA你不会得到代码，在这种情况下我上面说的软件可能值得一看。
顺便说一句，我最近要求提供一份关于测量RCS的旧应用说明。
Jvall亲切地提供了一份副本。
大约6周前我自己寻找关于RCS的帖子？
DaveEdited：drkirkby于2014年3月31日上午12:01



     以下为原文

  If you want a free solution,  you might want to look at the software for the very low cost VNWA

https://www.sdr-kits.net/

You can download the software for that for free and load a .s2p file and show the time domain data. Of course option 010 is better,  but it is not cheap. 

If the VNA is old and obsolete,  ask on the HP/Agilent Yahoo group and if you are lucky some kind sole might give you a code to enable option 010. In fact someone from Alltest  wrote there they would add the option for $300-$400, but there are a couple willing to do it for nothing on very old instruments. 

If you are working at X-band that means you are not using an 8753, for which codes to enable the option can be acquired. I know Techmaster Electronics do it on an 8720D,  since my VNA says on the calibration certificate that option 010 was added. I think for a PNA you won't get a code, in which case the software I said above might be worth looking at. 

BTW, I recently asked for an old Application Note on measuring RCS. Jvall kindly provided a copy.  Hunt for the post by myself about 6 weeks ago about RCS?

Dave

Edited by: drkirkby on Mar 31, 2014 12:01 AM

如果您发布响应的S1P或S2P文件，我会将其加载到我的PNA上并回发选项010结果。



     以下为原文

  If you post an S1P or S2P file of the response, I'll load it on my PNA and post back the option 010 result.

谢谢！
Dr_joel。
我已将测量的S11（freq，real，imaginary）附加到文本文件中。
不过，我不熟悉S1P或S2P格式。



     以下为原文

  Thanks! Dr_joel.

I have attached the measured S11 (freq, real, imaginary) in a text file. I am not familiar with the S1P or S2P format, though.

附件

• S11.dat4.9 KB
  

感谢您为我，drkirkby和Dr_joel发布结果！
我很高兴看到我的Matlab代码主要给出了正确答案：返回信号峰值的时间和幅度。
我可以肯定地看到应用一些窗口函数将有助于提高SNR。
当测量数据具有相似幅度的多个信号（在时域中）时，这可能是有用的。
对于dikirkby关于因子2的问题：我认为这仅仅取决于它是R还是T测量。
事实上，你的时间尺度（delta t）看起来都很好。
要获得物理长度或距离，您必须知道速度因子（您设置为1）。
对我来说，这种时域转换技术主要用于分析和诊断。
换句话说，如何解释时域数据并确定每个信号峰值的物理意义。
我猜这是个案。
但即使在这个简单的例子中，别名和多次反射的可能性也会使分析变得有些棘手。
我注意到你的两个时域数据都将起始时间设置为-5ns。
这是武断的还是有背后的原因？
这实际上是关于找到t = 0时间的问题。
致dikirkby：我会查找你建议的软件。
至于校准，我们没有电缆套件，绝对不是WG套件。
我们只使用短而不完美的50欧姆负载。
实际上，您可以看到我发布的S11数据在12 GHz附近不太好。
感谢您在eBay上了解该套件，我会请我的同事看一看。



     以下为原文

  Thanks for posting the results for me, drkirkby and Dr_joel!

I am glad to see that my Matlab code is giving me mostly the correct answer: the returning signal peak in terms of time and amplitude. I can definitely see that applying some windowing functions will help to improve the SNR. This is probably useful when the measured data have multiple signals with similar magnitude (in time domain).

To dikirkby's question on the factor of 2: I think it simply depends on whether it is R or T measurement. In fact, your time scale (delta t) looks all good. To get the physical length or distance, you have to know the velocity factor (which you set to 1).

To me, this time domain transformation technique is mostly useful for analysis and diagnosis. in other words, how to interpret the time domain data and determine the physical meaning of each signal peak. I guess this is case by case. But even in this simple example, the possibility on alias and multiple reflections can make the analysis somehow tricky.

I noticed that both of your time domain data set the starting time as -5ns. Is this arbitrary or there is a reason behind it? This was actually my question on finding the t=0 time.

To dikirkby: I will look up the software you suggested. As for the calibration, we don't have a cable kit, and definitely not the WG kit. we just used a short and a not perfect 50 ohm load. In fact, you can see that the S11 data I posted is not good near 12 GHz. Thanks for the head up about the kit on eBay, i will ask my colleague to take a look.

嗨，如果你甚至没有同轴校准套件，我不确定你的结果会如何搞砸。
在12 GHz时，便宜的负载很可能毫无用处，而且打开同轴电缆不会产生像8720D中任何一个校准套件那样的“开放”。
您将获得大量残留错误，因此所有S参数都会出现波纹。
我选择了-5ns作为开始时间，只是为了尽可能接近Joel。
所以问乔尔为什么选择-5 ns。
我认为这是因为它允许人们在t = 0时看到来自模拟脉冲的数据。
在eBay便宜的P波段波导校准套件已全部售出。
这看起来是最好的，并以56英镑（93美元）的价格出售。
http://www.ebay.co.uk/itm/Hewlett-Packard-P11644A-Calibration-Kit-/141161298073有人讨价还价！
令人难以置信的是，这些套件的售价如此之低。
我从来没有以一个非常便宜的价格买到一个，虽然我有一个P11644A，我付了很多钱，但仍然不是一个新的安捷伦的成本。
如果你想要一个*过于昂贵的*使用的X波段波导校准套件，这里有一个http://www.ebay.co.uk/itm/HP-Agilent-X11644A-Mechanical-Calibration-Kit-8-2-
to-12-4-GHz-WR-90- / 331102890349如果你想要价格合理的* X波段波导校准套件，这里有一个。
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=171246739026 Joel是时域方法专家 - 他的博士学位。
论文与它有关，而我的与VNA根本没有关系。
DaveEdited：drkirkby于2014年4月1日下午3:55



     以下为原文

  Hi,
If you don't even have a coaxial cal kit, I'm not sure how your results are going to be screwed up. At 12 GHz, a cheap load is likely to be pretty useless, and leaving the coax open is not going to create an "open" that is anything like any of the cal kits in the 8720D. You will get large residual errors, and so ripples on all S-parameters. 

I chose -5ns as the start time just to get it as close as I could to Joel. So ask Joel why he chose -5 ns. I assume it is because it allows one to see the data from the simulated impulse at t=0. 

The P-band waveguide cal kits that were on eBay cheap have all been sold. This looked to have been the best one, and sold for £56 ($93). 

http://www.ebay.co.uk/itm/Hewlett-Packard-P11644A-Calibration-Kit-/141161298073

Someone got a bargain! It is just unbelievable that those kits sold for so little. I never got one myself at that ridiculously cheap price, although I do have a P11644A which I paid a lot more for, though still not the cost of a new Agilent one. 

If you want an *excessively expensive* used X-band waveguide cal kit, there is one here 

http://www.ebay.co.uk/itm/HP-Agilent-X11644A-Mechanical-Calibration-Kit-8-2-to-12-4-GHz-WR-90-/331102890349

If you want a *very reasonably priced* X-band waveguide cal kit, there is one here. 

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=171246739026

Joel is an expert on the time-domain method - his Ph.D. thesis is related to it, whereas mine is not related to VNAs at all. 

Dave

Edited by: drkirkby on Apr 1, 2014 3:55 PM

你好
我有一个回波损耗（S11）与来自Vector网络分析仪的频率数据。
我应该使用ifft函数将数据转换为时域。
数据包括1 GHz至3GHz，1MHz频率步进回波损耗值我如何才能使用ifft功能？
提前致谢



     以下为原文

  Hi
I Have a Return loss (S11) versus frequency data from a Vector network analyzer. I should transform the data to time domain with ifft function.
The data includes from 1 GHz to 3GHz with 1MHz frequency step Return loss values 
How could i use ifft function for this purpose? 

Thanks in advance