This paper presents a new concept to implement tunable lowpass filters by employing slot resonators etched in the ground plane. The tenability is achieved with the use of switches with varactor diodes attached across the slots on the ground. The concept is demonstrated by considering 10-slots lowpass and 4-slots low pass filters. The Microstrip lines with a folded slot etched in the ground plane structure are modelled in multilayered media. To analyze this type of structure an iterative method based on the concept of waves is developed and adapted to determine features of very high frequency's electronic circuits in a planar wave guide. The analysis takes into account eventual coupling parasites. Experimental measurements are performed to validate the computation. The approach involves the mixed magnetic and electric filed equation technique and the wave concept iterative process which involves S-parameters extraction technique. In this sense, a program in FORTRAN has been elaborated to determine different parameters Sij characterizing the studied structure.
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