# components used to make a butterworth filter

I doing some amateur radio experimentation and want to create a bandpass filter. I believe that a Butterworth filter would be good because it has a flat frequency response in the pass band.

My center frequency is 1000Mhz and the bandwidth is 75 Mhz.

Since the the freq. is relatively high, I think the proper thing to do is use passive components in a ladder-type topology.

Does this seem like the right general path to follow for my design parameters?

Also, I'm going to build a circuit to do some testing. What should I on the lookout for in terms of my passive components (i.e. low ESR caps, etc.)

Thanks.

• 1. You need to decide how fast you want the skirts to roll off to choose the order of your filter 2. You'll want to model you filter with variation in the component values according to the tolerances of the parts you're considering using. May 20 '18 at 5:32
• I decided to use a 4th order Butterworth filter. Seemed like an it gives a reasonable trade-off in terms of the roll off in the stop band. As for components I was thinking of using "standard off the shelf tolerances" like 1% for my resistors. Is there a trade-off for tolerances? For example, like "one really wants a tight tolerance on the cap" for this or this reason. May 20 '18 at 5:49
• 0.1% resistors can be bought for reasonable prices. Better than 1% capacitors and inductors, not so much. Even 1% may be hard to find depending on the value you need. May 20 '18 at 5:56
• I'm finding, in my amateur radio hobby, that passive components aren't really so passive. May 20 '18 at 6:01
• Resistors for 1 GHz? You may want to rethink about it. Inductors should be used instead. Just make sure that the SRF of your capacitors and inductors is higher than your max operating frequency by some margin.
– Mike
May 20 '18 at 6:26

The wavelength at 1GHz is approximately 20cm ($v\approx\frac{2}{3}c$) for electrical signals. In order to be able to use a lumped system, you'll need the physical dimensions of the filter to be (preferably much) smaller than that in order to avoid reflections.