Broad-band power amplifier with an improved doubly tapered periodic bandgap PBG structure for harmonic tuning

We have designed and implemented three class A GaAs field-effect transistor (FET) power amplifiers. Two of these three cases have a 50 /spl Omega/ microstrip line utilizing an improved doubly tapered and a singly tapered periodic bandgap (PBG) structure for harmonic tuning respectively, while the other has only a 50 /spl Omega/ straight line. The doubly tapered PBG structure has more significantly improvement in output power and power added efficiency (PAE) than a singly tapered case and also has the ability to terminate the second and third harmonics. Measurement shows the improvement of output power and PAE with 0.5 dB and 4 % respectively by using a doubly PBG structure compared with a singly tapered one, and with 0.8 dB and 7 % improvement without utilizing a PBG structure.