How to stabilize this power amplifier?

I am trying to design a power amplifier using a bipolar common-base transistor operating as Class-C. It is the Microsemi 1014-12 that I use in pulsed RF from 1.2 to 1.3GHz. The bias circuitry is a simple 1/4wave line from VCC at 30V, and I have a couple bypass caps (10pF and 120pF) to ground from VCC. I also have a local storage cap of 4.7uF from VCC to ground.

Microsemi 1014-12 Datasheet

I'm using a loadpull measurement system to find the optimal source/load impedances, but I notice that I get an oscillation at 246MHz away from the fundamental of 1.29GHz with 33dBm of input power. In fact, if I drive the transistor harder, to say 34dBm, the oscillation goes away.

What can I do to get rid of this oscillation?

put at the input notch to 250M (RLC)

How are you doing the emitter bias?

The data sheet shows lumped element inductor place at a low impedance point on the collector matching network. Is that where you connected the line?. If you replace the inductor with a quarterwave transmission line, it is not the same ting, as it is not broadband. Also, 120 pf is not much of a ground at 200 MHz, you need something like a 0.1 uf in there also.

I do use a 1/4-wave line as a bias feed right next to the collector and emitter (low-impedance point on the matching network).

Right, the 120pF is for higher frequency. That's why I put in a 4.7uF too, but it doesn't seem to help. Or is 4.7uF too much?

What capacitor do you use as 4.7uF ?

Try to place capacitors, 1000pF, 0.01uF and 0.1uF of ceramic capacitor and 1uF or 4.7uF of chemical or tantalum capacitor.

Show me patterns of collector and emitter feeding.

It looks like I got the oscillations down by changing the caps to:
10pF Ceramic Chip, 120pF Ceramic Chip, 0.01uF Ceramic Chip, and 2.5uF Electrolytic.

Do you mean your problem could be resolved at last ?

See my appends in https://www.edaboard.com/thread204833.html

What I was trying to say was that 120 pf is too small, and the inductance in the 4.7 uf cap is so large that is it pretty much useless above a few MHz. You need something for the region in between.

I'm back to battling this oscillation problem.
The previous configuration worked until I changed the temperature of the DUT. At 60C, there's more oscillations.
What's a good combination of capacitor values at the VCC for a 1.25GHz center frequency after a 1/4-wave bias line?
It sounds like I need some values in the nF range too?

you can try 100pF+100nF+2.2uF+47uF(Tan)