[SOLVED] Size of box for radiation boundary

Hello All

I just want to ask you a vary basic question regarding radiation boundary box:

Instead of lambda/4 size of a box if i am making any random size box which is greater than lambda/4 in all the direction is it fine?
Does the size really matters?Is has to be exact lambda/4 greater or any random size is fine for printed loop antenna which works on Mhz range?

thQs

Hi,

To be in the far field region, you have to make sure that Radiation boundary will be at a distance of atleast Lamda/4 or greater. For some not so strongly radiating structures it far-field region could be achieved at a distance of Lamda/10. But in most cases, Radiation boundary should always be atleast at a distance of Lamda/4 or greater in order to get correct results for Radiation characteristics.

In case of loop antennas,they are classified in two categories,eletrically small and electrically large antennas. Electrically small loop antennas r those whose overall length(circumference)is usually less than about one-tenth of a wavelength(C< Lamda/10). whereas, Electrically large loop antennas have circumference which is about a free-space wavelength(C~ Lamda). Electrically small loop antennas are poor radiators and are mostly used for receiving in applications where antenna efficiency is not important but signal-to-noise ratio of the system is. Whereas electrically large loop antennas are good radiators and mostly used in directional arrays(one prime example is helical antenna).

Now you have to see your antenna dimensions as mentioned above and decide about the Radiation Box size. If you have an electrically small loop antenna then Lamda/10 distance is enough,otherwise stick with lamda/4 or greater distance for radiation box.

Hope it helps.
/SC

thQs sweetchoto

mine is electrically large one, so what i would like to know is in HFSS i will make a box for radiation boundary which should be lambda/4 large as its a electrically large,but say for lambda/4 my box size is coming to 5*10*15 cm^3 and say my lambda/4 is 1

so my radiation boundary box HAS TO BE 7*12*17 cm^3 or any thing larger than this dimension is fine?i really mean any size larger than the required. totally random like 9*18*25cm^3. does it affect on the result of finding S11??

again thQs for this knowledge.

Hi randy,

Any size greater than LAmda/4 will work fine and ll give u correct results. But why do you want to go for bigger size because it ll take more memory and time. But if you can afford it you can do it. No harm in it.

/SC

thQs sweetchoto

I was just wondering so that i just ask you eminent guys and moreover it can just give me rough idea that should it be precise or some what +- is fine, thats it. Actually I am still in the understanding part so dont have any complex system so for now i can just go ahead and try to see how to plot radiation pattern and S11 and all.

But will always keep in mind memory and processing time when it comes to actual designing part.

thQs again.

enjoy