Analytical solution of amplifier-antenna system's impedance matching requirement for reliable microwave transmitter

Abstract

In this paper, the integration of push-pull class B amplifier and antenna module have been proposed. The high efficiency and low distortion of push-pull class B due to its differential feeding technique makes it a viable candidate as a power amplifier. The aperture-coupled antenna structure is used in this work as it offers the designer various methods to effectively adjust the variables thereby making way for more efficient configuration which can be fabricated on system-on-chip. Moreover, this enables a wide range of values that can be chosen on the Smith Chart thus allowing the conditions needed for odd-mode matching to be satisfied. This matching requirement is specific for only a given transistor and in this work by incorporating bandstop filters made of resonant stubs it has been possible to filter harmonic power up to 3rd harmonic. The frequency of operation of the integrated push-pull transmitting amplifier during simulation is at 2.06 GHz. The Wilkinson power divider, power coupler, phase shifter and bias decoupling circuits have been employed so as to efficiently integrate the push-pull class B power amplifier with the differentially fed aperture coupled antenna. Two types of antenna were studied whereby one was designed with the conventional 50 ω environment while the other makes use of the complex value impedance. Parametric study was also performed on both types of antennas so as to investigate the effects it has on the impedance matching requirements. Finally, the prototype was realized through fabrication and measurements were performed at fundamental frequencies and up to 3rd harmonics to show gain at fundamental component and filtering of 2nd and 3rd harmonic.