Hi, my name is Eric Diez. I am an engineer at Agilent Technologies. Many customers have
asked us how to generate and analyze digitally modulated signals at millimeter-wave frequencies.
And this is becoming increasingly important, as new applications appear at these high frequencies
– things like automotive radar or wireless HD video transmission. So today, we are going
to demonstrate creating and analyzing a 64-QAM signal at 65 GHz. And to do that, we will
be using a PSG vector signal generator, a PSG analog signal generator, an EXA signal
analyzer running the 89600 vector signal analysis software. Let’s take a closer look at how
to set up this measurement. To generate our signal, let’s begin with the vector PSG.
We are creating our 64-QAM signal internally and modulating a 15 GHz carrier. And that
is mean output here on the RF output. Now using the internal baseband generator, we
can generate up to 80 MHz of modulation bandwidth. But some applications require more bandwidth.
So in those cases, we use the external IQ inputs on the rear panel and an arbitrary
waveform generator that can create up to 2 GHz of modulation bandwidth. So that gets
us very wide modulation, up to 44 GHz. But in this case, we want to go up to 65 GHz,
and we will use an up-converting technique. And to do that, I need a local oscillator.
So for that, I will use the analog PSG. It is putting out a 25 GHz signal with +17 dBm.
Now the reason I use the high level +17 dBm output is because that helps us get better
conversion efficiency in the mixer. Now to perform the actual up-conversion, I am using
this mixer right here, mounted on the front panel. And, normally, this would be an option
in the analog PSG called “Option H65,” that is mounted behind the rear panel. I am
using it here externally, so it helps us visualize the signal flow better. Now this particular
mixer has an integrated doubler, so that doubles our 25 GHz signal from the PSG to 50 GHz.
We combine that 50 GHz signal now with the 15 GHz IF from the vector PSG, and that is
what gets us to 65 GHz. So that is how we generate our modulated signal up at the millimeter
frequency. Let us take a look at how we analyze the signal now. Now to analyze our signal,
we will be using the EXA Signal Analyzer, which is part of Agilent’s family of X-Series
signal analyzers. This happens to be the 44 GHz model, and it has the external mixing
option. The external mixer we are using is right here. That is one of our smart mixers.
And we call it a smart mixer because it has onboard memory that has all the correction
values for this particular mixer stored inside. When I connect this to the EXA, I am using
a USB cable. And when I plug that in, it will automatically identify which mixer I am using,
and it will download those correction factors into the memory of the EXA. That corrects
for the frequency response of the smart mixer, giving us the very best amplitude accuracy.
We also have this RF cable that takes the LO signal from the EXA, runs it to the smart
mixer. And then the IF signal comes back through the same cable into the instrument. Inside
the EXA, we are using the 89600 VSA software. This is a really powerful software package
that lets us analyze a wide variety of signals and modulation types. And you will note here
on the display, we have, in the upper left quadrant, our familiar constellation diagram
for a 64 QAM signal. Then down here, we have all the measurement results that were calculated
with the software. And, in particular, I will point out that we have a very good EVM number.
It is running about 1.6 percent, which is pretty remarkable, considering we are looking
at fairly high-order modulation up at 65 GHz. So in this short demonstration, we have been
able to show how you can generate and analyze a digitally moderated signal up at 65 GHz
with low EVM. If you would like to find out more information about Agilent’s millimeter-wave
solutions, please visit the URL shown here or talk to your Agilent sales representative.
Thanks for watching.