Multi-Octave VHF Push-Pull Power Amplifier Using Coaxial Balun

A multi-octave push-pull power amplifier has been designed for VHF band applications. In order to validate the design, two 10-watt power amplifiers are fabricated and tested from 70 MHz to 350 MHz. The balun used in the push-pull configuration is designed using a coaxial transmission line, which can handle high power at the output. The coaxial line is encapsulated by ferrite beads to improve its performance in the lower frequency band. The balun has been characterized in terms of its mixed-mode S-parameters. The proposed push-pull architecture is tested using a 10 MHz long-term evolution signal. The second and fourth harmonics have been suppressed by more than 40 dB and 50 dB, respectively, between 70 MHz to 350 MHz.