Practical considerations for a summing amplifier
Since zero dBm is only 0.632 volts PeakPeak into 50 Ohms, you need 6dB higher at about 1.2 volts PP.

Consider this circuit







simulate this circuit &ndash; Schematic created using CircuitLab

The common-base summing node has about 1 ohm impedance (plus base inductance). There will be some small crosstalk between the 2 inputs. An opamp will, similarly, not be able to implement a zero-voltage virtual-ground (Vin-) at 150MHz.

The standard 2N3904 has very low beta at 150MHz (maybe 2). Try faster devices. Watch the power dissipation, and watch how the heat can exit the bipolars, and R2 and R5 pulldown.