矢网测S11时有毛刺,为什么呢？

1. points不够?
2. 没有smooth?

校准的时候采用的信号幅度过小?

怀疑是校准问题 或者有信号泄露

信号功率小, 为何就会有这样的现象呢?
我们用了0dBm和-25dBm的都搞过了 :(

points不够的话, 应该漏测啊, 即这些毛刺可能根本看不见了.
另外,毛刺大概S11有-10dB左右, 而其它地方S11则-25dB左右

有匹配负载,S11是正常的,说明校准是好的啊. 难道还有其它检测标准?
至于泄露信号, 我觉得也是, 估计是DUT被矢网激励后,产生的什么东东....

你的DUT是否是主动元件?
我之前遇到过类似的状况，
当时是测天线开关，最后发现其供电有问题会引起这种状况。

是有源的,而且带开关的, TDD开关
你说的供电是指天线开关的供电吗? 有什么问题呢? 谢谢！

没有校准好

Your problem is to identify the source of trouble: it is VNA's problem or DUT's problem?
To find out the reason,
1, check the 8753 and what you talked high-end VNA, see if there are any setting difference, especially the smooth settings for the high-end VNA, the normal setting should be 1~3% aperture; you will got two possible results:
     a, settings are identical, then the DUT and high-end VNA are working correctly, your 8753 has some problem
     b, 8753 has no smooth setting (this is very likely happened, I have no experience with this model), and the settings can not the identical, and when you off the smooth funtion of the high-end VNA, dips and spurs appear too, then it is your DUT's problem
2, check your DUT power supply, using spectrum analyzer to probe output signals, check if proper DC block is used, check the stability of the DUT;

but personally, I think it is your DUT's problem instead of VNA's; it is very likely caused by the instability problem or your DC power supply problem

Thank you very much for your comments.
I have some questions on them:
   1, do you mean to probe DC supply line with SPA ?
      I only know SPA can probe some self oscillated RF signal.
     But I donot know how to check DC power supply, would you please tell me in detail ?
     Many thanks.
   2,DC block
      Waht kind of this problem? DC leak into RF signal with badly DC blocked?

   3, DC power supply problem
       What kind of this poblem, instability caused by DC supply such as not correctlly bypassed ? Or DC supply itself has some problem ?
      Thanks a lot！

So it seems you are sure that it is your DUT's problem, right?
all these things are suggestion for you to check, I know many guys in their circuit design paid little attention to DC part; Actually, most of the time it is the DC part which cause the trouble. that's why I said to check your DC.
following is the answer to your problem which may be helpful to you:
RF chocks used are not omnipotent. bad chock will leak RF power to DC part (in the worst case, RF signal at DC part is about 10dB lower than your main path); complicated feed back, attenuation will result. If your circuit is a high gain, high frequency unit; then these signals will cause spurs and ripples on both S21 and S11 curves;
spectrum analyzer can help you to determine how bad this leakage is in the DC part; usually with some absorbing materials or redesign your DC part can reduce these leakage efficiently (be careful to use DC blocker to your spectrum analyzer when you probe)
for the DC block, I mean sometimes DC leakage to the output, which will damage the VNA (some VNA models have no built-in DC block). these are usually caused by DC block capacitor failure; spurs appears in such situation (one of my friends spoiled his VNA in the MEMS tests because of such problem)

Thanks a million ！

你是不是校准的带宽太宽了，如果是这样的话，只有分开测试了。

yellowtoot
是个强人啊！
   用频谱仪检查DC POWER SUPPLY的过程能告诉一下吗?  
   谢谢！