Hi,
I am using a QPA2612 PA in high power X band transmitter. We are observing lower-than-expected maximum RF output power and gain at multiple input powers/frequencies.
For example, applying a 2 dBm 10 GHz signal to the QPA2612 input yields only a 27 dBm output, resulting in a gain of 25 dB. Based on the plot shown in the datasheet and copied below, I expect a gain closer to 30 dB. The output power also saturates at lower levels than expected, I have only been able to get ~ 32 dBm output at 10 GHz.
My PA DC operating point is 250 mA and 24V as listed in the datasheet. The PA operates in a room at room temperature and is mounted onto a large heatsink. I am using Cinch 142-1731-876 SMA connectors to minimize losses at the output/input connections.
The biggest factors I’ve noted that may be causing my lower gain/power at saturation are my board layout and signal input. I am using a coplanar waveguide transmission line with a characteristic impedance of 50 ohms. I noticed you used microstrip on the eval board; is it better suited? I am also applying a CW signal at the input as opposed to the signal with a “Pulse Width = 100 us, Duty Cycle = 10%” listed in the datasheet. Would this be causing the lower gain and output power I am experiencing? I figure it would cause some degeneration but not > 8 dB in Psat.
Thanks