Hello engineers
To achieve a sidelobe level of -30 dB in a slot linear array, I calculated the amplitude and offset coefficients in Matlab, but when I enter the offsets, I do not reach that sidelobe level. I checked with a field probe and saw that I read the distribution of the field amplitude for each slot in volts per meter and it did not match the obtained amplitudes, for example, the amplitude coefficients are [0.1915 0.4636 0.7843 1 1 0.7843 0.4636 0.1915].(N=8)
My question: Is it correct to manually change the offsets so that, for example, 100% of the amplitude reaches slots 4 and 5, for example, its maximum is 1400 volts per meter, now 78.43% for slots 3 and 6, which is 1100 volts per square meter, and so on until the end... Is this method correct?
I'm not sure what you are doing wrong, or what you suggest doing.
If you are putting a feed on each slot separately, then you can use the coefficients in the table as the feed amplitude for each slot, for example using a waveguide feed to each slot. If you have a feed network, then you need to take into account the feed losses to each element. In an end-fed array, the first will be coupled by 0.1915, but the second will be missing this much power, and will need a higher coupling coefficient to get the required amplitude. The last element will need to be 100% coupled to use up all the remaining power, if you plan to use it all - you may want to waste some power in a load beyond this so that the last element doesn't have 100% coupling.
If you have an array that is close to the right coupling values, it is fine to adjust the slot couplings until the V/m are in the right ratio. I would simulate the slot to find out how the coupling varies so that I could get very close with my second try.
Mr. Vahid, when we talk about a array in practical domain, it will have a feed network. This feed network will have one input port and will have number of output port equal to number of radiating elements. Array coefficients are noting but how feed network is proportionally divide the input power feed to each of elements in the array.
Now in CST, Array module accept the inputs in narmlised coefficients. Now if you aren't getting desired side lobe, in this case first you go back to your matlab check your coding. Once you got correct coefficients. In second step again in matlab apply these coefficients to array and see you get output pattern with desire sidelobe. In this way first verify you coefficients in the matlab. Once you got the correct coefficient,Then in third step plunge these coefficient into CST. You will get your desire pattern.
For more details pl. Go through a book on anteena by R.E. Elliot. He has explane the hole concept.
Mr. Vahid, when we talk about a array in practical domain, it will have a feed network. This feed network will have one input port and will have number of output port equal to number of radiating elements. Array coefficients are noting but how feed network is proportionally divide the input power feed to each of elements in the array.
Now in CST, Array module accept the inputs in narmlised coefficients. Now if you aren't getting desired side lobe, in this case first you go back to your matlab check your coding. Once you got correct coefficients. In second step again in matlab apply these coefficients to array and see you get output pattern with desire sidelobe. In this way first verify you coefficients in the matlab. Once you got the correct coefficient,Then in third step plunge these coefficient into CST. You will get your desire pattern.
For more details pl. Go through a book on anteena by R.E. Elliot. He has explane the hole concept.
Thank you for your guidance.
A resonant array with 8 slots fed by a waveguide with angled slots. Now I want to know how much amplitude reaches each slot when I offset it from the center line of the waveguide? From the center slots as we go towards the side slots, the coupling should decrease, that is, it should be closer to the center line of the waveguide. Is there a way to know whether I reached the same amplitude coefficients with this amount of offset or not, that is, can I see those coefficients in the cst software?
The second question is that when I draw a side lobe level of -35 dB with Chebyshev, in the far field diagram, the Cartesian coordinates of the first lobe after the main lobe should be -35?
My second question is very important, please help me. Thank you.
Simulate the slots in the waveguide using CST, with the offset as a parameter, and also the angle, so that you can tell what the coupling is for each offset and angle. This is what simulation codes are good for. Then you can draw design curves and select the offset and angle you need for the coupling you want.
Mr. Vahid, In your two day back query you have requested that you second query is very important. In that regard when we apply -35 dB, Chebyshev
distribution to an antenna array it radiation pattern will show not only first side lobe is 35 db below with respect to main lobe but all other side lobe will also be of same order as first lobe.
Pl do not get confuse with the Cartesian coordinates of the first lobe after the main lobe should be -35. The Cartesian coordinates is just a way of plotting a graph in x-y manner, like other graphical representation like polar, spherical ect.
Once you completed the model in CST including supplying the excitation coefficient to model. You pl. Run the Simulation. Once it complicated. First check the SWR, this you will find in 1D Results. If you get accepted SWR then plot the Fairfield (This you will find in Fairfield button/folder at last). Here you can check the radiation pattern in polar, Cartesian, 3D format
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