parabolic antenna - shallow dish - any expert ?

[mauloftin]

deep dish vs shallow dish

Hi,
is there any expert on the parabolic antenna? I need find feed for shallow dish, but I need small side lobes and good gain. I have problem with spillover.

Thank you

 

[DaveN]

corugated antenna+book

Hi,
is there any expert on the parabolic antenna? I need find feed for shallow dish, but I need small side lobes and good gain. I have problem with spillover.

Thank you

hi there

Visit http://w1ghz.org/ Paul Wade's site and go to the
W1GHZ Microwave Antenna Book Online link it has just about everything you need to know about
the design of dish antennae and feeds for them (also covered are other uWave antennae)
Paul's knowledge on the subject is well respected worldwide

Dave
VK2TDN

 

[mauloftin]

antenna parabolic sydney

hi there

Visit http://w1ghz.org/ Paul Wade's site and go to the
W1GHZ Microwave Antenna Book Online link it has just about everything you need to know about
the design of dish antennae and feeds for them (also covered are other uWave antennae)
Paul's knowledge on the subject is well respected worldwide

Dave
VK2TDN

Thank, yes, I know it, it is basic online book - but there is not answer on my question, what can I do, if i have shallow dish and I need good gain and small spilover. There is only 3 types feeds: Conical horn, rectangular horn ans corrugated conical horn. It is no good for my shallow dish.

Dual mode horn is good, but very frequency-dependent and main lobe is very "close" = bad gain ......

So i need something like in attachment - it is conical horn with dielectric. It is good - have good side lobe, frequency "independent", but I need a little more "flat" main lobe

Thank

 

[Azulykit]

define me the parts of parabolic antennas

Low sidelobes and high gain are contrary goals. Define your target parameters, frequency limits and dish parameters. If you do a good job there you may get more meaningful answers and suggestions.

 

[mauloftin]

sidelobe dish

Low sidelobes and high gain are contrary goals. Define your target parameters, frequency limits and dish parameters. If you do a good job there you may get more meaningful answers and suggestions.

Hi,
yes, I know, that the gain and sidelobes are contrary goals - it is typical problem with design in microwave technolgy, that the parameters are contrary goals .

A have dish with high f/D = 0.36 (and 0.38), that mean: it is shallow parabola. D=cca 900mm, f = 10.7-11.7 GHz, class of antenna should be 2, rather 3.

For small sidelobe of parabolic antenna you need small sidelobe of feed, about -20 dBi on the angle cca 70° (angle of parabola edge) - it is spillover and the class 2 have on the angle 110° (180-70) about -20 dBi (attachment).
So I have the feed with small sidelobe (conical horn with dielectric), but the main lobe is a little bit "closed" (radiation angle is small), that mean: illumination loss and that mean worse gain (attachment farfield.jpg).

I hope, that you understand me

 

[DaveN]

dish for antina europe pic

Then again you could just use the good ol' Penny Feed these are very popular with the Amateur (Ham) fraternity
and are particularly suited for shallow dishes with f/D ratios of 0.25-0.3 area
NO its not professional, but hell it works VERY well
I have to say after reading many postings on this forum by various people how much they seem to rely on design
software instead of just getting out there and building and experimenting with different systems and observe the results.

I am teasing you just a little bit

In my own experimental activities I have played with a number of different feeds for various styles and sizes of dish antennae
deep, shallow, offset, prime focus, cassigrain

seriously tho.....

You don't need to reinvent the wheel to produce a decent working system its already been done for you
you can easily just go out and buy the dishes and associated matching feeds.
BUT I do like to experiment
And I learn a heck of a lot in the process .... nothing beats practical experience

cheers
Dave N
VK2TDN
www.sydneystormcity.com/10ghzlog.htm for some examples

 

[mauloftin]

feed for parabolic dishes czech

Penny Feed

Hi,
thank, but I am not sure, what do you mean "Penny feed", is it similar as chaparral feed (http://www.w1ghz.org/10g/chapfeed.gif) or corrugated horn (**broken link removed**) ?

Of course, I do not need to reinvent the wheel to produce a decent working system - but a can not find good feed for shallow dish with good gain and good sidelobe.

problem is only one: European Telecommunications Standards Institute and
their class of antenna



My question: can you tell me, what is class of your antenna ?

 

[DaveN]

dual mode feed 5.7 et 10 ghz

Have a look at that link I put after my signature in the last post

it will take you to my 10GHz logbook that has photo diaries of my hilltop/etc outings ...there will see 2 of the dishes I have used
the white dish (the middle pic in the 1st 3 pics) is a penny feed

see this reference for a pennyfeed explanation.....
http://www.microwave-museum.org/exhibits/mwm0024.htm

my main dish, who knows what class it is, in all the years of working on microwaves you are the first I have
heard that has mentioned classes of dish antennae you will have to tell me what the different classes stand for
maybe its some oddball european standard that doesnt apply in other countries ??

...my dish is a standard oval shaped offset dish used for satellite TVRO it is 700mm x 600mm and gives me ~ 35dB gain
on 10GHz and in excess of 42 dB on 24 GHz. if you scroll further down my
10ghz log page you will see closeups
of the feed I am using. it is a converted 12GHz TVRO LNA that I have removed the electronics from and mounted a SMA
connector that protrudes into the waveguide as a ~6mm probe. This feed is a chaparral feed, as you showed pix of in your previous post.

I do appreciate that you may be working on professional systems and are constrained by certain Euro standards.
I am just digressing a bit from the seriousness of the earlier posts just to show you some of the other possibilities
and things that can be done in the non-pro world

If you read some of my diary you will see that with that I have easily done in excess of 200km on SSB (single side band) with only +13dBm (20mW) of transmitter power
I have found it pretty amazing at what can be done on these freq's with low power!!!

cheers
Dave

 

[mauloftin]

lna feed dish

see this reference for a pennyfeed explanation.....
http://www.microwave-museum.org/exhibits/mwm0024.htm

my main dish, who knows what class it is, in all the years of working on microwaves you are the first I have
heard that has mentioned classes of dish antennae you will have to tell me what the different classes stand for
maybe its some oddball european standard that doesnt apply in other countries ??


I do appreciate that you may be working on professional systems and are constrained by certain Euro standards.

cheers
Dave

So penny feed - is it one type of back-feed, yes? For example as hat-feed ()? - it is very bad for shallow dish - it is problem with ETSI, because tha back-feed have very high sidelobe => the parabolic antenna have high sidelobe

ETSI - you can see to attachment. I am from Czech Republic - (Central Europe ) and if we want to use parabolic antenna (transmitting side) we must follow class of antenna - most often class 2, somewhere 3.

so the problem is shallow dish - it have high sidelobe. You can use "collar" or very deep dish (f/D<cca 0.18) - but it is expensive, i want to find feed with small sidelobe but with flat main lobe (I am not sure, if you understand the concept of "flat main lobe", i think that the radiation angle is "high" - follow )



ETSI - http://www.etsi.org/WebSite/AboutETSI/AboutEtsi.aspx

 

[DaveN]

dish backfeed antenna

Thanks for those references they will keep me reading for a while.
Its always interesting to see what is happening in other parts of the world.

I guess your could describle the pennyfeed as a form of back feed
I hadn't seen that hatfeed design you linked to I'm not sure why you call it a bad design with hi side lobes as the
article states that its is a good design because of the low sidelobes
quote ...
The main advantage of this feed configuration is improved dish antenna efficiency with a very simple mechanical setup.
Design goals were:
• Linear / circular polarization capabilities
• Good axial ratio (with CP)
• Low cross-polarization losses
• -13 dB dish edge taper for low side lobes

I see it uses circular waveguide where the pennyfeed uses the more normal rectangular wg.
Just as an aside ... bit of history.... the name penny feed cmes from the original use of a copper coin... an english penny
~ 1 inch (~25mm) in diam. The photo in that article shows a reflector that looks substantially larger than 25-30 mm

I remember the first horn feed I had on my offset dish it was WAY too big and
as a result I had no real worry about side
lobes spilling over the edge of the dish .... as I wasnt event fully illuminating the dish. Thats when I moved to the old
LNA feed that was ideally suited for the offset dish.

For a prime focus dish, the ony time I wouldnt use a penny feed is if I wanted a multiband feed. example covering...
5.7 and 10 GHz or 10 and 24GHz where the work done by Paul W1GHZ and others have produced really good dual band feeds.

Thanks for your responses I have really enjoyed the discussions
its been very worthwhile

Dave
VK2TDN

 

[mauloftin]

parabolic antenna with 10 ghz

article states that its is a good design because of the low sidelobes
quote ...
.....
Design goals were:
...
• -13 dB dish edge taper for low side lobes

Yes and no. See at figure 10 of articles - you can see radiation pattern - that is not class 2 of antenna - this is problem, there is high sidelobe.

The problem: picture in atachment.