AWR eBooks

RF Electronics Chapter 7: RF Filters Page 227 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. The design process is illustrated using the Bessel filter with an 18.48 MHz centre frequency and 2 MHz bandwidth filter, in the previous design. The filter design requires 4 resonators. Inductors with an inductance of 200 nH and an unloaded Q 0 of 100 are available. In LC resonators, the Q of the capacitors used is generally much higher than the Q of the inductors, so that by using equation 7.6, the resonator has a normalised q of: 8 . 10 100 48 . 18 2 0 0 Q F BW q c . From the Bessel filter tables in Zverev, the nearest value corresponds to a q 0 of 10.048 and results in an insertion loss of 1.85 dB. Since the actual Q is slightly higher, one should obtain an actual insertion loss that is slightly less as is evident from figures 31, 32 and 35. The corresponding K and Q values from this filter table for this value of q 0 are: q 1 = 0.3891, q 4 = 0.5098, k 12 = 1.7120, k 23 = 0.6794 and k 34 = 0.8512. Entering those values in the LC Bandpass Filter design equations on the global definitions page of the accompanying Cadence AWR DE project file for figures 7.29 - 7.31 program gives the filter values as shown in figure 7.29. Figure 7.29. Global definitions LC bandpass filter design equations for a Bessel filter. As can be seen, using equations in Cadence AWR DE in this way is very powerful. Just changing some input variables in these equations will calculate and simulate any 4 resonator bandpass filter. The equations can easily be modified for different numbers of resonators. The equations in figure 7.29 also include capacitive impedance transformation equations, to allow any desired input and output impedances to be obtained. In addition, the K and Q equations for Butterworth filters have been included RF Electronics: Design and Simulation 227 www.cadence.com/go/awr

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