Notch filter at 125MHz

[namtey]

I need to design a notch filter that blocks 125MHz (subharmonic) but passes 250MHz (fundamental). I am relatively new to high frequency filters and was hoping someone could offer some advice on what topology would be best for this type of filter? Active/passive/lumped/distributed/chip solution?

 

[JimB]

You give no context for where or how this filter is to be used, but any solution will almost certainly be a passive filter.

One filter which is very easy to implement at these frequencies is the "Quarter Wave Stub".
Take a length of co-ax cable, quarter of a wavelength long at the frequency to be attenuated, connect on end to the place where you want the attenuation and leave the other end open circuit. This will present a short circut at the quarter wave frequency and an open circuit at twice the frequency.

JimB