Experimental Study of the Buried Vias Effect on Reflection Symmetric Modal Filter Performance

The paper considers the influence of buried vias in the reference conductor on time and frequency characteristics of a four-layer reflection symmetric modal filter (MF). The prototype of the reflection symmetric MF was developed in two versions: with and without buried vias. For the first time, the effect which buried vias has on the characteristics of reflection symmetric MFs was studied experimentally. The decomposition of an ultrashort pulse (USP) into a sequence of pulses of lower amplitude is shown. The influence of buried vias on the MF characteristic impedance was estimated. The frequency dependences of the transmission and reflection coefficients in the range from 0 to 32 GHz were obtained. Moreover, practical recommendations are given for the design of multilayer reflection symmetric devices based on coupled lines in this paper. The results are useful for further research because the configuration of a four-layer reflection symmetric MF without buried vias reduces its cost.