It is unclear whether the output power values specified in the HMC862 datasheet are measured single-ended or differential.

Answer: The HMC862 was measured with single ended outputs.

What is the minimum output frequency of the HMC862A

Answer : It can work down to 100M/8. The datasheet does not explicitly specify the minimum output frequency. However it can be inferred from the minimum input frequency (100 MHz) and the maximum divider ratio (8), making the lowest output frequency 12.5 MHz? On Page 10 of the datasheet, the plot illustrates the phase noise for a divider setting of 8 with a 100 MHz input signal. This can be confirmed by inspection of Fig 23. The Red trace represents the measured phase noise at 12.5 MHz (with a 100MHz input square wave ) for a divide-by-8 operation. The signal's slew rate has a significant impact on phase noise. In this case, a 100 MHz square wave or a 5 dBm 100 MHz sine wave was used. The slower slew rate of the sine wave causes noticeable phase noise degradation compared to the square wave. Reducing the sine wave amplitude (further lowering the slew rate) will degrade the phase noise performance further.