A microstrip filter direct-coupled amplifier based on active coupling matrix synthesis

This paper presents a methodology of designing an amplifier integrated with a microstrip filter using an active coupling matrix. The microstrip filter is directly coupled to the active device, and the integrated filter amplifier can achieve filtering as well as matching functionalities, simultaneously, eliminating the need for separate matching networks. The filter amplifier is represented by an active coupling matrix, with additional columns and rows in the matrix corresponding to the active transistor. The matrix can be used to calculate the S-parameter responses (i.e., the return loss and the gain) and the initial dimensions of the integrated device. Moreover, the integration of a filter and an amplifier leads to a reduced loss and a more compact architecture of the devices. An X-band microstrip filter amplifier has been designed and demonstrated as an example. Microstrip technology has been chosen because of its appealing advantages of easy fabrication, low cost, and most importantly, easy integration with active devices.