RF Electronics Chapter 7: RF Filters Page 251
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
It is possible to specify a sloping passband attenuation to compensate for this, but this
will result in a higher insertion loss and a worse return loss. The measured performance
of the second filter is shown in blue in figure 7.65 and it has a centre frequency of 984
MHz compared to the 1 GHz specification. The measured bandwidth is 92 MHz
compared to the 70 MHz specification. This may be sufficiently close to satisfy the
required specifications. If this is inadequate, then another filter needs to be designed.
Figure 7.65. Measured and designed frequency response of the interdigital filter.
Figure 7.66. Microstrip interdigital filter, 70 MHz bandwidth at 1 GHz.
Figure 7.66 shows the resulting filter realisation. For this realisation, bends are
incorporated in the input and output transmission lines, so that the input and output
connectors can be mounted on the same panel. Interdigital filters are often used in
commercial designs as can be seen in figure 7.67, which is part of a microwave layout
produced by Codan in Adelaide, South Australia. Comparing figures 7.66 and 7.67,
RF Electronics: Design and Simulation
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