Electronics > RF, Microwave, Ham Radio

Looking for cheap-ish generator (oscillator) module, 2.45 GHz, 10 W

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hanakp:
@LaserSteve: the problems with reflected power is an excellent point, I can see it could upset the oscillator's feedback and bring the LDMOS into dangerous operating conditions. The project lead wasn't testing me, BTW - he is retirement-age guy who spent last 20 years around magnetrons and other high-power stuff. He's simply lost touch with low-power solid-state RF circuits, that's why he brought me in (even if I'm no expert myself).

@NiHaoMike: many thanks, we're going to try the bulgarian power amplifier, because it comes with case and everything. My plan is to make a small PCB with VCO, attenutator and pre-amplifier and mount it inside the PA's case. Then I will remove the input SMA and directly connect the PCBs with a short coax.

But the case is thin (19 mm) and there is not much headroom between the PA PCB and lid, so my PCB shouldn't use any tall components. I looked at metal can VCOs like ROS-2490 from Minicircuits , but all have over 4 mm. Is there any fundamental difference between these metal can and integrated VCOs like Maxim MAX2750AUA? Do they have better aging, temperature stability or something? Lower output power is no problem, since my PCB needs a pre-amplifier anyway.

radiolistener:
you can use magnetron M-62 or M-95, it has at least 20 W power with anode current 39 mA and anode Voltage 1.35 kV.
The frequency is 2401–2499 MHz.

For 10 W output, just put anode current about 22-23 mA
For 1 W output, just put anode current about 5 mA

hanakp:
I finally got my hands on the SG Laboratory Ltd amplifier for Es'Hail 2 satellite uplink and did some basic measurements. First I measured its frequency response with Siglent SSA 3032X generator/analyzer combo at 0 dBm input power (limit of the internal generator). I'm attaching the result below, it has 30 dB gain (1 W output power) in the target band. But it has much wider bandwidth than advertised, it employs NXP MMG30271B as pre-amplifier and Ampleon BLP9G0722-20G LDMOS as the power stage. However, I was mostly interested in how it behaves at 2.45 GHz and higher power levels. I used Agilent N9310A and R&S FSL18 for that, although I have less confidence in these measurements, because the analyzer was partially damaged a few years back (somebody put too much power to the input). At full 28 V supply voltage, the gain is:

0 dBm input => 1.3 W output, 31 dB gain
+11.1 dBm input => 10.2 W output, 29 dB gain
+13.3 dBm input => 13.5 W output, 28 dB gain
+17.0 dBm input => 20 W output, 26 dB gain

I actually missed 1 dB compression point, because I didn't expect it would lie below 10 W. That's mostly irrelevant for my application, however. I was more interested in how bad harmonics the amplifier produces at the extremes of the operational parameters - as I mentioned earlier, my plan is to control the output power via supply voltage. But my worries were unfounded, I couldn't find any 2nd or 3rd order hamonics during my experiments - the amplifier has an output microstrip filter which apparently does a great job. I'm attaching FSL18 screenshots which I took at 28 V supply/20 W power and 8.2 V/2.5 W power.

Overally, the amplifier is nicely made, the aluminium cooling base plate is 7 mm thick. It uses semiconductors from "respectable" producers, 78M05 regulator is from ONSemi and vox and PTT circuits employ Microchip MCP6001 opamps. Trimmer for vox hold time is from Bourns. It also has two identical directional couplers with detector diodes and RC filters at the output. They're denoted FWD and REF (forward and reflected?), I presume they're used to tune the amplifier during production. In the future, I may use them to detect and automatically shut down the amplifier when someone runs it without proper load. There is 7 mm headroom between components and lid, so I'll have no problem fitting my 2.45 GHz generator board inside. I plan to mount in on the lid above the vox circuits (upper left corner), to minimize the chance it would upset the PA circuits.

hanakp:
It's been a while, but I've successfully designed and tested a small VCO PCB to drive the bulgarian power amplifier. It worked, but would be too laborious for production. So the project head contracted the bulgarian guy to produce similar VCO + PA on a single PCB for us. Which means I can share my design here.

As I previously planned, I mounted my PCB inside the amplifier case, it should be obvious from the photos. I'm also attaching Eagle 9.6.2 and Gerber files in case anyone wanted to build it. I put most design notes directly into the schematic.

I removed original input SMA connector and replaced it with U.FL inside the case. But it was a real chore to solder it in correctly, because the space was tight. If I did it again, I'd probably solder a thin coax directly to the PCB, althought I'm not sure how it would affect impedance matching. And of course I mounted the PA on a heatsink and added a fan.

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