# Radiation Source placement and waveguide parameters for Horn Antenna

I am designing ("arranging", actually) a horn antenna for a 77-81 GHz Radar. My module has a patch antenna which can't be placed inside the waveguide for some reasons. After the patch antenna, we have a radome to protect the patch antenna. Then, the waveguide starts which then flares into the horn antenna.

In all the literature, all discussion was on the horn design (i.e. getting optimal horn parameters D and L for given λ), and waveguide minimum diameter (d) for given λ. Now, after getting the optimum horn, I have a few doubts about waveguide and radiation source placement:

1. Where should ideally be the source placed inside the waveguide?
2. If it can't be placed inside the waveguide (like in my case), how far can it be?

2.1. Also, in this case, if we use the minimum-diameter waveguide, would it provide a sudden change in impedance for the radiation coming from patch antenna into free-air and then into radome and then into the waveguide? So, should we make the waveguide with a larger diameter?

2.2. Is the waveguide even required in this case?

3. Does the thickness of the waveguide surface or horn surface have any affect?

## UPDATE-1:

Conventionally, horn waveguides are fed with pins. I found that what I am trying to do is to feed the horn with patch antenna, and the technical term for this is : "patch excited horn antenna", as discussed here. However, patch antenna is always put inside the waveguide/horn entrance in most designs. In my design, it is put outside the horn. So, the design is tricky.

• Why use a horn at all? Could you maybe use a dish type reflector or something? – mkeith May 30 at 8:54
• Yes, @mkeith that is what I have been feeling now too, that a parabolic reflector would be better. – shivams May 30 at 11:50