LPDA Feed vs Horn feed for reflector

Hello all!

I have seen the paper attached below, and number of other papers describing the use of LPDA as feed for reflector antennas, now my question is , what will be the pros and cons OR what benefits we'l get if we use LPDA as feed instead of Horn

Can anyone please compare horn and LPDA for the following quantities:

Gain
Size
Aperture blockage
impedance
Bandwidth
Efficiency
Taper loss
any other special point that needs to be considered?


View attachment JP26.pdf
View attachment log periodic feed for lens and reflectors.pdf

My Design: : What I'm trying to design is an LPDA as feed for 0.6m reflector. LPDA will cover the range of 8-14 or 8-16 GHz (size will be quite reduced for these frequencies i guess? )

As the paper clearly explains, the LPDA is suitable for extremely wideband operation, and it was shown that its features can be used also with a parabolic dish. All features you listed are described extensively.
Horn primary radiator in a parabolic antenna is usually not so wideband; It usually ends a rectangular waveguide feed, so the antenna frequency response is determined by it.
There are also specially modified wideband horn antennas that can be used as a primary feed of the parabolic reflector.

With your 0.6 m parabolic reflector, your LPDAs covering 8-14 or 8-16 GHz would offer a higher gain; some matching problems should be expected due to dish reflection.

OK.Would you please take a look on the attached file "design Specs.pdf" and then the referred files attached (1.pdf & 2.pdf) and could you please suggest me some solutions related to the problems i have described??
I have done a lot of literature survey and selected these paper for my design.
Best Regards
Kamal

Can anyone please compare horn and LPDA for the following quantities:

Click to expand...

Gain = The gain is affected by the size of the dish for the freq of use not by the feed say for a 0.6m dish
the gain is going to increase as the freq goes up. There's plenty of calculators on the www to work that out.

Size = The LPA will be much less bulky than than a horn feed

Aperture blockage = The feedhorn will have a bit more aperture blockage than a LPA

impedance = you can have a 50 Ohm feed to coax for either horn or LPA

Bandwidth = The LPA is very wide band, the horn feed isnt. Its relatively easy to get at least 8GHz bandwidth from a LPA, I use one that easily covers 2Ghz - 11.5GHz
The Horn feed is relatively narrow band, 2GHz (give or take a bit) either side of the centre freq.

Efficiency = is primarily affected by the illumination of the reflector, incorrectly illuminating the dish will lower the efficiency

Taper loss = not sure how to answer that one ?


cheers
Dave

I think that both papers are well written and give you a good guidance. You should expect more study and experiments to achieve a good result. Notice that paper authors did such work and expect you to do yours.

I was asking about the value of R1, or the maximum size of the antenna, I'm confused about it.plus please discuss the issues, my design and assumptions I have made.I wanted to confirm if i'm on the right track

bukhari917 said:

I was asking about the value of R1, or the maximum size of the antenna, I'm confused about it.plus please discuss the issues, my design and assumptions I have made.I wanted to confirm if i'm on the right track

Click to expand...

The antenna aperture size determines the main lobe (beam) width and gain. Both will vary with frequency; you have to decide on the min. and max..

---------- Post added at 19:26 ---------- Previous post was at 19:22 ----------

I think all details on logarithmic antenna are well described in the papers you refer to. The only remaining thing for you is to scale it to your frequency band.

jiripolivka said:

The antenna aperture size determines the main lobe (beam) width and gain. Both will vary with frequency; you have to decide on the min. and max..

Click to expand...

Yup exactly ! and for the freq range you are considering 8 - 14GHz and a 0.6m dish you may only just get a 10deg (-3dB point) beamwidth at 8GHz and at 14GHz you will be looking ~ 6deg beamwidth. ( just reasonable approximations without doing the exact maths)

for example my 1 metre dish @ 10.3 GHz gives ~ 5 deg beamwidth, the same dish at 24GHz gives ~ 2 deg beamwidth
The larger the dish, the tighter the beamwidth, for a given freq or conversely increasing freq for a fixed dish size also gives a tighter beamwidth

cheers
Dave