The unloaded Q factor is calculated with the use of the relationship w x 3
where โฅ is the VSWR of input coupling circuit with matched 1 output load and โฅ is the VSWR of output coupling circuit 2 with matched input load. The results of Figure 6 show that unloaded Q factors of 1000 over a 1-GHz tuning bandwidth can be achieved with this filter, leading to a vast improvement in both bandwidth and Q factor over conventionally tuned MIC ring resonators reported so far in the open literature.
The layout of the proposed filter, which measures 6.9 mm 2 , is shown in Figure 8. The input and output RFOW pads are on the left and right of the chip. Three dc pads are provided for the biasing of the active devices, and there is an extra pad for the grounding of the chip. For the active devices, a standard biasing technique, based on three and a half turn inductors for rf chokes, was used. Note also that separate through-GaAs via holes were used for the grounding of each component to ensure a low-resistance path to ground and to avoid parasitics, which can be disastrous at the frequency of operation. The MMIC filter is currently being fabricated through EUROPRACTICE, and the results of practical measurements, to be carried out at the University of Manchester Institute of Science and Technology, will be reported.