Helix antenna: bandwidth

Dear Sirs,

I have a question about Helix antenna:

how much is the frequency bandwidth (S11 < -15 dB at 1.2 GHz)? I mean, typical value...

Any book about helix antenna is welcome.

Thanks in advance,

Lupin

Hi, Lupin:

I think it is related to the dimensions of your helix. There is an old book on it.

Hisrmatsu Nakono, Helical and Spiral Antennas --- A Numerical Approach, Research Studies Press.

Regards,

This antenna was described in the 1950 era Antenna book by Kraus who invented it. The bandwidth is usually 2:1.

Let's say that I need a narrow band e.g. 1% at 1.2 GHz...

Is it possible to get this bandwidth or do I have to work with the Helix large bandwidth putting a filter after this antenna?

I need to avoid undesired incoming signal..

Thanks in advance,

Lupin

You would be better off by putting a filter at the input of your receiver instead of using the antenna for filtering.

The antennas we build and use have a rough 10 % bandwidth, but the attenuation outside band is not very sharp.
Usually an antenna ( except patch and some aereonautical antennas ) have a quite wide bandwidth.
Also take care that as the banwidth decrease, the antenna is more sensibl to the surrounding environment, especially radomes and ground plane.

Mandi

A helix antenna normally has two modes. When it is not very long, it is narrow banded. When it is long enough, it suddenly becomes wide band.