下載
下載

下載手冊、產品規格表、軟體等等:

下載類型
機型或關鍵字

Calculating RF Power from IQ Samples

Vector signal analyzers like Tektronix Real-Time Spectrum analyzers operate by converting the incoming RF signal into quadrature baseband (IQ) samples vs. time.  All of the measurements and results that can be displayed, from simple spectrum measurements to complex modulation analysis, are computed from these IQ samples.

RF20Power20Calculations

One common calculation that is performed on the IQ data is to determine the RF power vs. time.  The formula used to compute RF power is remarkably simple.  It’s interesting to review how this formula is derived.

 

The I and Q values represent the peak value of the in-phase and quadrature components of the RF signal vector.  The Pythagorean Theorem tells us that peak RF signal voltage is equal to:

1

 

By definition, the I and Q values are the peak values of the sinusoidal quadrature components of the RF signal.  Thus, the RMS value of the RF signal is given by:

2_0

 

Substituting the equation for the peak voltage:

 

3

 

In a 50Ω system, the RF power is given by:

4

 

…and substituting the equation for the RMS voltage into the power equation:

5

…which simplifies to:

   

6

 

Power in dBm is given by:

7

…which simplifies to:

8

 

As we can see, the computation of RF power boils down to very simple equations for RF power expressed in watts or dBm.

 

A downloadable PDF version of this blog is available here.

部落客

Electrochemistry Experts

部落格文章: 7
Tektronix Experts

部落格文章: 258
David Pereles

部落格文章: 18
Joseph Gorley

部落格文章: 2
Service Experts

部落格文章: 6
Brian Hensley

部落格文章: 2
Christopher Loberg

部落格文章: 5
Alan Wolke

部落格文章: 21
Andrea Vinci

部落格文章: 1