In this case of design, it is better to study the circular horn antenna before starting the design and simulation, Muny antenna books give more details, like Balanis ...

You have to know that important parameters are:

- Aperture size,

- the length,

- the size of the waveguide (standard size)

Thanks for response.

I´ve tried rectangular antennas, antennas with wires that disrupt the flow of the waves (like simple filter), corrugated antennas rectangular, round and circular too. Maybe It´s not even possible do It better. I will continue to try simulate..

There is more information about what I need solve.

The antenna runs on f = 2400MHz, wavelenght cca λ = 12,5cm. The antenna is excited by the magnetron. Because of that, whole device must be very safe. 

What i want or better is on the link below (nice example), but this is unuseful for me, because around the antenna will be safety zone bounded using metal plates and this will disrupts radiation characteristics. And will occur again normal horn antenna :-/

http://www.ets-lindgren.com/pdf/3117.pdf

If you mean that you want a wide beam, you should decrease the size of the antenna. ETS 3117 horn antenna shows the widest beam at lower frequencies, that is, the electrically smaller the antenna is, the less directive its radiation pattern.

As like other researcher are saying, you will have to be very careful about antenna parameters and changing from rectangular to circular will create a complexity during standing wave pattern, i mean, your VSWR will be improved as compared to rectangular but corrugated structure is just like slow wave structure, it means there are possibility to get more reflection, so before design of such antenna, you have to have prepare for all electromagnetic properties where matching impedance plays an important role.

Thanks

Generally, at particular frequency you will find various horn antennas dimensions.

To enhance Bandwidth, you may try with higher dimensions of opening mouth of the horn antenna. Go with some optimization processes.

I thank you all for answers.

The electrical properties of the antenna, in this case, is not so much important. The problem is, that the customer does not know what type of magnetron will be used.

My task was to find a horn antenna, which has the widest radiation distribution.

Recently, I finished simulation of the most successful model (in a red box on the picture). I will still continue with work to find some better solution, but I believe that the final antenna will be not much different.

Hi Zdenek

The wider the aperture is made higher the gain is. It is a physical rule (Fourier Transform of the fields at the aperture results in the Farfield pattern).

The corrugation will not play such a large role decreasing the gain as making the aperture smaller. I'd advise you instead of a horn use a simple open waveguide, coupled to the magnetron. Gains for this sort of antenna are around 8 dB, which is not very directive.

Other thing to remember, the matching should be taken care of at the input port. If you forget about the impedance you will end up with a lousy transition, most energy bouncing back to the magnetron (which may turn out even dangerous).