RF Electronics Chapter 7: RF Filters Page 252
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
shows that the procedure for earthing the grounded end of the resonator to the bottom
layer ground-plane is slightly different. The positioning of the vias in figure 7.66 is the
most likely cause of the centre frequency being 2% low.
As the number of resonators increases, the stopband attenuation does not significantly
increase. As a result, hairpin or direct-coupled filters are a better choice when a very high
close-in stopband attenuation is required. Interdigital filters are however smaller than
hairpin of direct-coupled filters and they are thus the best filter to use when PCB space is
at a premium.
Figure 7.67. PCB showing three interdigital filters. (Codan [15]).
Direct-Coupled Resonator Filters
Figure 7.68. Transmission line coupled resonators.
RF Electronics: Design and Simulation
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