N5241A和SMC+低输入功率下的测量问题

你好。
我正在准备一个C波段到L波段接收机的测试计划，其输入功率范围为-70到-95dBm，增益约为65dB。
我有一个N5241A，我想用它来产生增益，群延迟，回波损耗（SMC +相位方法），C / IM3和噪声系数测量。
在准备测试计划时，我使用现成的硬件组合了一个混音器，放大器和滤波器系统来模拟接收器。
我一直在PNA-X和仿真器的工作台上工作，到目前为止，我已经能够成功地进行群延迟，回波损耗和增益测量，输入电平范围为-70到-80dBm。
但是，一旦我开始以较低功率工作，我的群延迟和输入回波损耗测量值就会从各自走线上的所有噪声中难以辨别。
我能够通过降低IF带宽来降低噪声。
这改善了输入回波损耗测量，但我仍然遇到组延迟问题。
无论降低IF带宽多少，群延迟轨迹的形状在-80dBm以下的不同功率水平下都不一致;
然而，迹线上的噪音确实有所改善。
我担心我的PNA-X设置可能是我的群延迟问题的原因。
我使用端口1作为C波段输入端口，端口3作为LO，端口2作为L波段输出端口。
端口1上的源衰减器设置为65dB（我在此源衰减级别进行了相位参考校准和S参数校准）。
所有接收器上的衰减器设置为0dB。
我担心使用这种实现方式耦合到端口1接收器的功率远低于接收器的灵敏度（例如，在-80dBm和15dB耦合因子下，到R1接收器的功率将为-95dBm）。
我想如果实际上我的实现是一个问题，那么我可以在端口1和我的测试电缆之间添加一个30dB的焊盘然后将源衰减器降低到35dB，从而将耦合到接收器的功率增加30dB并仍然保持输入
我需要的功率范围。
所以，我的问题是：1。通过将源衰减器设置为65dB，我实际上是否影响了PNA-X的测量能力？
2.我的替代实施方法是否可以解决问题？
谢谢您的帮助！！！
-担



     以下为原文

  Hello.  I am preparing a test plan for a C-band to L-band receiver that has a input power range of -70 to -95dBm with approximately 65dB of gain.  I have a N5241A that I want to use for making the gain, group delay, return loss (SMC+phase method), C/IM3 and noise figure measurements.  I put together a mixer, amplifier and filter system using off-the-shelf hardware to emulate the receiver while preparing the test plan.
I've been working on the bench with the PNA-X and the emulator and so far I've been able to make successful group delay, return loss and gain measurements for input levels from -70 to -80dBm.  However, once I begin working at lower power levels, my group delay and input return loss measurements are indiscernible from all of the noise present on their respective traces.  I was able to reduce the noise by decreasing the IF bandwidth.  This improved the input return loss measurement but I still am having problems with my group delay.  The shape of the group delay trace is not consistent at different power levels below -80dBm no matter how much I lower the IF bandwidth; however the noise on the trace did improve.

I'm concerned that my setup of the PNA-X may be the cause of my group delay problem.  I'm using port 1 as the C-band input port, port 3 as the LO and Port 2 as the L-band output port.  The source attenuator on port 1 is set to 65dB (I did my phase reference cal and S-parameter cal at this source attenuation level).  The attenuators on all of the receivers are set to 0dB.

I'm concerned that the power being coupled to the Port 1 receivers is dropping too far below the receiver's sensitivity using this implementation (for example, at -80dBm and 15dB coupling factor, the power getting to the R1 receiver would be -95dBm).  I figured that if in fact my implementation is a problem, then I could add a 30dB pad in between Port 1 and my test cable and then drop the source attenuator to 35dB thereby increasing the power coupled to the receivers by 30dB and still maintain the input power range that I need.

So, my questions are:
1. Am I in fact affecting the measurement capability of the PNA-X by setting the source attenuator to 65dB?
2. Is my alternative method of implementation going to solve the problem?

Thanks for the help!!!

-Dan