Transversal and recursive filters useable in a diplexer

Abstract

Transversal and recursive filters having an input propagation lumped element network with a band pass filter response, a low pass filter response, or a high pass filter response, and an output propagation network having a low pass frequency response, a high pass frequency response, or a band pass frequency response are described. Weighting means including a plurality of field effect transistors are used to successively couple the input propagation network and the output propagation network. The general shape or response of the transversal filter is provided by choosing the characteristics of the input and output propagation networks in relation to the desired filter response. With the general shape provided by the propagation networks rather than only by the transversal elements, fewer transversal elements are required to provide a desired response. Thus, the transversal filters are smaller which increases the manufacturability of the circuit and reduces the cost of the circuit particularly when fabricated as a monolithic microwave integrated circuit. Further, for transversal filters having a bandpass characteristic, harmonic sub-bands generated at high frequencies are eliminated by use of lumped element networks having cutoff frequencies coinciding with the frequency skirts or bandedges of the filter.