What is wrong with the output of this amplifier? It's amazing.
时间：04-07
整理：3721RD
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Now I am dealing with a mixer and it is cascaded with a MMIC amplifier, Gali-5+,from the mini-circuits, to amplify the IF signals. The LO frequency is 2855MHz, +13dBm,while the RF input is 985MHz.-28dBm; When I tested after the mixer, the result is as follows ( all refers to dBm ):
985MHz：-55.93；1.97GHz：-106.4；
885MHz：-99.12；4825MHz：-102.1；
2855MHz：-30.92；5.71GHz：-27.35；8565MHz：-30.82；11.42G：-53.42；
1.87GHz：-34.82；3.84GHz：-35.12.
They were RF input and its harmonic, the third order distortion, the LO remains and its harmonics, the IF frequency ( upper and downside).
However, when I tested after the amplifier, the results came:
985MHz：-39.97；1.97GHz：-74.32；
885MHz：-83.13；4825MHz：-92.7；
2855MHz：-17.99；5.71G：-22.21；8565MHz：-39.71；11.42G：-64.41；
1.87GHz：-19.92；3.84GHz：-24.85.
As we can see, the amplifier works normally from 885MHz to 4825MHz with a gain varying from 14dB to 10dB. Everything is OK, except that 1.97GHz got a gain of about 32dB. That is amazing. I couldn't imagine a small MMIC amplifier have a gain of 30dB. So I made another experiment, in which I chose the 1.97GHz as an individual input for the amplifier, then to my disappointment, the gain is just 15dB as normal. I have added a 3dB π attenuator for a good match in the input stage of the amplifier.
So would anyone have met such problems or would bring me some suggestions?
I doubt that the 985MHz LO remains causes some harmonic for 1970MHz after the amplifying and this harmonic plays a dominant role, comparing the 1970MHz's liner amplifying results .
Any reply is welcome.
985MHz：-55.93；1.97GHz：-106.4；
885MHz：-99.12；4825MHz：-102.1；
2855MHz：-30.92；5.71GHz：-27.35；8565MHz：-30.82；11.42G：-53.42；
1.87GHz：-34.82；3.84GHz：-35.12.
They were RF input and its harmonic, the third order distortion, the LO remains and its harmonics, the IF frequency ( upper and downside).
However, when I tested after the amplifier, the results came:
985MHz：-39.97；1.97GHz：-74.32；
885MHz：-83.13；4825MHz：-92.7；
2855MHz：-17.99；5.71G：-22.21；8565MHz：-39.71；11.42G：-64.41；
1.87GHz：-19.92；3.84GHz：-24.85.
As we can see, the amplifier works normally from 885MHz to 4825MHz with a gain varying from 14dB to 10dB. Everything is OK, except that 1.97GHz got a gain of about 32dB. That is amazing. I couldn't imagine a small MMIC amplifier have a gain of 30dB. So I made another experiment, in which I chose the 1.97GHz as an individual input for the amplifier, then to my disappointment, the gain is just 15dB as normal. I have added a 3dB π attenuator for a good match in the input stage of the amplifier.
So would anyone have met such problems or would bring me some suggestions?
I doubt that the 985MHz LO remains causes some harmonic for 1970MHz after the amplifying and this harmonic plays a dominant role, comparing the 1970MHz's liner amplifying results .
Any reply is welcome.
You don't tell exactly about the measurement setup. Is it a spectrum analyzer output? A spectrum analyzer isn't measuring gain.
For the particular 1970 MHz component, you have mainly demonstrated, that the amplifier has some 2nd order harmonics which isn't surprizing basically. The mixer, which is apparently a balanced type, hasn't it.
A single-tone measurement of the amplifier with variable input level can be expected to show the amplifier generated harmonics much clearer. You should be aware however of generator and spectrum analyzer non-linearity as well.
1.97GHz component is from 985MHz input. just change RF freq to 990MHz, probably you will find the same at 1.98GHz
this is due to imds.