Substrate Integrated Waveguide Filter-Amplifier Design Using Active Coupling Matrix Technique

This article presents a comprehensive active N + 4 coupling matrix approach for the design of integrated filter-amplifier. The feedback between gate and drain, which is neglected in a previous work, is considered, which improves the accuracy of the coupling matrix model for transistors. More importantly, the relationship between the coupling matrix and the noise figure is also established, which extends the coupling matrix method to tackle noise-related circuit functions. Substrate integrated waveguide (SIW) filters are used to implement an integrated X-band filter-amplifier design and to validate the design approach in terms of return loss, gain, and noise. Compared with rectangular waveguide, SIW is utilized for its appealing advantages, such as lower production cost, easier fabrication, and most importantly easier integration with active components. A second-order filtering circuit is applied to simultaneously match the input and output of the transistor. The integration reduces the losses from the intermediate networks in conventional designs, which is particularly important when the frequencies go higher. The measurements agree very well with the simulations in terms of S-parameters, gains, and noise figures.