The filters were implemented in grounded coplanar waveguide (GCPW) media , and their design was carried out via a full-wave electromagnetic simulator . For the lumped-element realization, the simulation entailed varying the inductive (magnetic) coupling between the spiral inductors of the LC resonators, which was achieved by optimizing the filter response as a function of the separation between the inductors. The halfwavelength resonator-coupled filter version can be designed using coupler synthesis tools and fine-tuned with the full-wave solver. In addition, in order to assess attainable tuning ranges, simulations were conducted while setting the varactor parallel plate gap to various distances: 6 mm, 5 mm, and 4 mm.
It is interesting to note that, in this simulation, the lumped-element version exhibited a downward shift of 6.4% in center frequency with a capacitor gap reduction of 2 mm, while the distributed resonator version exhibited a downward shift of 2.6% for a varactor gap reduction of 1 mm. Also shown in Figure 5.14 are RF chokes to permit the noninvasive application of the varactor control voltage.