When is it more desirable to use an m-derived filter over a constant-k filter?

Using an m-derived filter is indeed more desirable when you need more attenuation at a certain frequency. This type of filter is designed specifically to provide better frequency response characteristics, particularly in terms of selectivity and attenuation. The m-derived filter achieves this by adding additional reactive components that enhance the filter's response at specific frequencies, allowing it to attenuate unwanted signals more effectively than a constant-k filter.

Constant-k filters, while simpler to design and analyze, do not provide the same level of performance in terms of attenuation at certain frequencies. They are better suited for applications where a flat passband and simple construction are prioritized over steep roll-off characteristics. In contrast, m-derived filters are advantageous in situations where precise control over the filter characteristics is necessary, making them a preferable choice for achieving higher attenuation levels at targeted frequencies.