Yagi Antenna Basics

I am learning about antennas, and i need to build a Yagi for my project. I have some doubts on basic yagi structure.

1. I am designing 4 element yagi for 800-900 mhz ISM band. After
fabricating, can i put that inside a plastic enclosure ? will that
affect performance ?

2. How to fix elements ? , one of the free software i downloaded from internet
asking me, following three options. How to choose one of them, and how
does it matters ?

a. Elements Insulated thru Boom
b. Elements Insulated from Boom
c. Element Not insulated from Boom


Regards.

No, you can put it in plast

c. is right.

Yes, you can put the Yagi antenna inside of the plastic enclosure almost without problems. Most of the antenna manufacturers are doing this for high-frequency Yagi?s to protect the elements.

All 3 variants that you specified are right and each one need a dedicated simulation, because it affects in different mode the Yagi performances.
The first variant (a) usually is used in Long-Yagi antennas where can get the highest gain and directivity.
The last variant (c) is the cheapest one in terms of mechanic design of the antenna.

The size of the elements change according to the type of the boom.
if the boom is metalic and not insulated you have to take that into consideration.
(the length of the elements is shortened).
I guess this is the reason they are asking the three options.
In order not to bother yourself with that the best thing to do is use a non-metalic boom (wood or plastic (better:more presentable)).

be carefull some programs do not give accurate results for the length of the elements. Try to compare to the theory you learned.
Good Luck