为什么输出功率测量会有差异

嗨Daras，我们正在进行测量，占空比为5％。
我们在脉冲条件下测量S21并增强响应校准。
对于峰值功率测量，我们使用N1911A功率计和N1921A峰值功率传感器。
对于峰值功率测量，我们在执行源功率校准后将CW设置为CW模式。
我发现，与从网络分析仪增益测量计算的功率相比，功率计显示的值更低。
Rgds Nsm



     以下为原文

  Hi Daras,

we are doing the measurement with a duty cycle of  5%. We measure the S21 under the pulse condition with an enhanced response cal.

for the peak power measurement we are using the N1911A power meter with the N1921A peak power sensor. For the peak power measurement, we set the NA in the CW mode after performing a source power cal. I find that the power meter shows a lower value as compared to the power computed from the network analyzer gain measurement.

Rgds
Nsm

什么型号的网络分析仪正在使用（如果它是PNA，请求表示固件转速）？
您是使用网络分析仪参考接收器测量输入功率还是假设使用源功率校准，输入功率将是精确且平坦的？
您说输入回波损耗很差，因此通常意味着输送到DUT的功率可能与源功率校准期间使用功率传感器测量的功率不完全相同。



     以下为原文

  What model network analyzer are using (if it is a PNA, pleas also indicate the firmware rev)?  Are you measuring the input power with the network analyzer reference receiver or are you assuming that with the source power cal, the input power is going to be exact and flat?  You said that the input return loss is very poor, so that usually means that the power delivered to the DUT may not be exactly the power that you measured with a power sensor during the source power cal.

> {quote：title = nsm写道：} {quote}>您是否建议使用推荐接收器测量测量时的源功率？
是 - 大多数功率传感器具有非常好的匹配性，因此当您使用具有非常好的回波损耗的传感器测量端口功率时，来自源的大部分功率将被传递到传感器。
另一方面，您的DUT具有较差的回波损耗，反映了更多的功率回到源。
经过校正的S21测量可以解决这种不匹配问题，但如果您想使用S21来计算输出功率，则不能假设平坦的输入事件功率。
为了使用PNA测量输入功率，您还需要至少执行R1接收器功率校准。
但是，为了获得最准确的测量结果，您需要进行匹配校正的功率测量。
如果您碰巧选择083或082，则可以设置标量混频器测量（SMC），偏移为0 Hz，并使用OPwr测量，这将是DUT的匹配校正输出功率。



     以下为原文

  > {quote:title=nsm wrote:}{quote}
> Would you recommend that , I measure the source power at the time of measurement using the refernce receiver?

Yes - Most power sensors have very good match and therefore when you measure the port power with a sensor with a very good return loss, most of the power from the source will be delivered to the sensor.  On the other hand your DUT that has a poor return loss, reflects more of the power back into the source.  A corrected S21 measurement accounts for this mismatch, but if you want to use the S21 to compute the output power, you can't assume a flat input incident power.

In order to measure the input power with your PNA, you will also need to do at least an R1 Receiver Power cal.  However, for the most accurate measurement you will need a match-corrected power measurement.  If you happen to have option 083 or 082, you can setup an Scalar Mixer measurement (SMC) with a 0 Hz offset and Simply use the OPwr measurement, which will be the match-corrected output power of your DUT.

嗨Daras，我有的网络anlayzer没有选项082或083.我想澄清另外一点。
我做了一个源功率校准，然后是一个增强的再现校准，用于进行S21测量。
我认为在源功率校准期间指定的容差范围内，源功率将是平坦的。
对于上述S21测量，我添加输入功率以计算估计的o / p功率。
然后，我通过将网络分析仪设置为具有源功率校准的CW扫描模式并将其用作源来测量峰值功率计上设备的输出功率。
通过这种设置，功率计读数的差异程度和测得的S21峰值功率的计算值是多少？
我怎么估计这个？
Rgds nsm



     以下为原文

  Hi Daras,

The network anlayzer that I have does not have option 082 or 083. 


I would like to clarify one additional point. I have done a source power cal and then an enhanced resposne cal for doing the S21 measurement. I would presume the source power would be flat to the extent of the tolerence specified during the source power cal.

To the above S21 measurement, I add the input power to compute the estimated o/p power. 

Then i measure the output power of the device on a peak power meter by setting the network analyzer to CW sweep mode with a source power cal and using it as the source.

With this set up what could be the extent of the difference in the power meter readings and the value computed of the peak power from the measured S21? How can I estimate this?

Rgds
nsm

我不得不咨询Dr_joel，以确保我把这部分做得正确（他可能实际上是在这里自称，因为他是一个很好的权力讨论的吸盘:-)）所以让我们先看看传递到a的功率方程式
负载（P~del~）作为负载的入射功率（P~inc~）和S11的函数：h2。
P~del~ = P~inc~ *（1 - | S11 | ^ 2）功率传感器的内置校准因子校正了此偏移，因为功率传感器的S11是在工厂测量的。
因此，功率传感器产生的读数就像传感器具有完美的50欧姆匹配（在许多情况下不是很远）。
然而，他们还假设连接到功率传感器的源（源匹配）的伽马也是50欧姆，在VNA源的情况下通常不是很真实。
因此，实际上，入射功率随伽马源和传感器的匹配而变化：h2。
P~inc~ = P~source_to_50ohm~ /（1-Gamma~source~ * S11）因此，累积效果是传递给功率传感器并由功率传感器测量的功率可能与传送到DUT的功率不同
在相同的设定功率水平下由相同的源。
差异的大小与（1-Gamma~source~ * S11~psensor~）和（1-Gamma~source~ * S11~dut~）的差异有关。
PNA中匹配校正的功率测量值进行额外校正，以便在测量输入或输出功率时，考虑源/负载匹配的差异。
一种简单的方法可以改善功率传感器测量的输出功率与（S21 * InputPwr）计算的输出功率之间的一致性，即在连接到DUT输入端的电缆末端放置一个3-6 dB的焊盘。
并且您应该在该垫的末尾执行源功率校准和增强的响应校准。
包含垫将减少校准和测量之间的源/负载匹配项的差异。
希望这能回答你的问题。



     以下为原文

  I had to consult with Dr_joel to make sure I get this part right (and he may actually chime in here himself as he is a sucker for a good power discussion :-))

So let's start by looking at the equation for power delivered to a load (P ~del~ ) as a function of the incident power (P ~inc~ ) and S11 of the load:

h2. P ~del~ = P ~inc~ * (1 - |S11|^2)

The built-in cal factors of the power sensors correct for this offset since the S11 of the power sensor is measured in the factory.  So the readings produced by a power sensor are as if the sensor had a perfect 50 ohm match (which in many cases is not very far off).  However, they also assume that the gamma of the source (source match) attached to the power sensor is also 50 ohms, which in the case of the source of a VNA is usually not very true.  So in effect, the incident power changes as a product of the gamma source and sensor match:

h2. P ~inc~ = P ~source_to_50ohm~ / (1 - Gamma ~source~ * S11)

So the accumulative effect of this is that the power delivered to and measured by a power sensor may not be the same as the power delivered to a DUT by the same source at the same set power level.  the magnitude of the difference is related to the difference in the (1 - Gamma ~source~ * S11 ~psensor~ ) and (1 - Gamma ~source~ * S11 ~dut~ ).  The match corrected power measurements in the PNA make this additional correction so that when input or output powers are measured the difference in source/load matches are accounted for.

A simple way for you to improve the agreement between the output power measured by a power sensor and output power computed by (S21 * InputPwr) is to put a 3-6 dB pad at the end of the cable connected to the input of the DUT and you should perform your source power cal and enhanced response cal at the end of that pad.  The inclusion of the pad will reduce the difference in source/load match terms between the calibration and measurements.

Hope this answers your question.

嗨daras，谢谢你的清晰解释。
方程确实帮我解释了错误。
但是，整个设置是自动测试装置的一部分。在输入处添加一个打击垫很困难。是否还有其他方法可以进行此测量？
Rgds mahesh



     以下为原文

  Hi daras,

Thank you for the lucid explanation. The equations does help me account for the errors. However, the whole setup is a part of an automated test set.It would be difficult to add a pad at the input.Would there be any other method to do this measurement?

Rgds
mahesh