The invention is a dual band power amplifier with a small footprint having excellent band-toband isolation. An improved second and fourth harmonic trap at the output of the low band power amplifier comprises a first capacitance shunted to ground placed in series with an inductance, the inductance preferably in the form of a transmission line of predetermined length, and a second capacitance coupled between an intermediate point of the transmission line inductance and ground. Band-to-band isolation can be additively increased by further forming a ground loop between the outputs of the two poweramplifiers. The ground loop further isolates the high band amplifier from the low band amplifier by causing the magnetic fields generated around the output wire bonds of the lower band power amplifierto set up circulating currents primarily in the ground loop, rather than coupling into the output wire bonds of the higher band power amplifier.