LDMOS is one of the most reliable high power transistors. I think it is OK for LEO satellites.

This is a kind of initial check for the transistor. If you do load-pull simulations, it is enough. After designing matching networks, it is necessary to check the stability of all circuit. Matching networks can create undesired resonances at out of operation band which can cause oscillation.

For higher frequency, you can use R//C type network. I attached an example. You need to find suitable values which is not degrading the gain depending on your operating frequency.

Hi Aparna,
That transistor is conditionally stable. It can oscillate. Therefore you have to consider it during matching network design. Since the gain of the device is not very high at that region, it is not difficult to make your amplifier almost unconditionally stable.
You need to check the stability factor with input and output matching network.
You can see this article: https://www.researchgate.net/publication/325101221_Refine_biasing_networks_for_high_PA_low-frequency_stability
Osman

In my previous job, we had the same problem with a SiGe transistor. We copied the application circuit at the datasheet, but it was really bad regarding wideband stability. A low-pass type network including biasing circuit worked well. But it degraded noise performance a little. If you are not a big customer, usually vendors do not reply your e-mails.

Hi Sara,
1) If your RF system uses 50 ohm, then, of course, your amplifier output should be 50 ohm. But your transistor drain should see impedance ZL. ZL can be an impedance regarding design requirements such as the highest efficiency, max output power, etc.
2) You can simulate any part of smith chart, you can set it at schematic. ADS examples usually use reflection value to define the sweep are for load-pull simulations. Therefore, you need to calculate reflection if you use impedance data as reference. There are lots of online calculators from impedance to reflection or other way around.
3) Terminations of the harmonics are important. But you have to be careful. If you have a transistor model including package parasitics, bonding wires, etc., you may need a specific impedance value instead of short or open to maximize the performance. There are many studies about harmonics terminations. If you are a beginner, I recommend books at first.