Asymmetrical Spurline Resonator Design and its Application to Power Amplifiers

An improved spurline structure with two rejection bands is presented in this paper, which consists of asymmetrical spurline resonators and embedded directly into microstrip line. Asymmetrical spurline resonators provide dual-bandgap characteristics and slow-wave effect. Furthermore, asymmetrical spurline structure with dual rejection bands is proposed to reduce the higher harmonics of microwave power amplifiers. To evaluate the effect of asymmetrical spurline resonators on microwave amplifiers, two InGaP HBT power amplifiers were designed and fabricated. One of them has asymmetrical spurline structure at the output section, while the other has a conventional 50-Omega microstrip line only. Results show that asymmetrical spurline structure suppresses the second and third harmonics more than 27 dB at the output and yields improved power added efficiency (PAE) and output power by 6-8% and 1-4%, respectively.