Master-Master or Signal booster or etc?

Hello guys,

I am using Fatek PLC's to communicate with each other as a Master & Slave through zigbee which is connected through RS485. And I succeed. But the issue is that I have to communicate each other at a distance of about 2km where zigbee out of range to each other.

I am bit confused here;
1) whether I use RF booster? Does it work?
2) Should I introduce extra PLC as a repeater between master slave? But this(extra added) PLC repeater also become as a master(Master Repeater).or any idea?

Most important I can using Fatek Protocol or Modbus RTU or Modbus ASCII prootcol.

I would try a repeater like the following:
https://www.commfront.com/products/industrial-rs485-rs422-repeater-extender-converter?variant=9208590211

You could try converting the signal to ethernet:
http://www.bb-elec.com/Products/Ethernet-Serial-Servers-Gateways.aspx
https://www.ubnt.com/airmax/nanostationm/

I would not introduce an extra PLC unless you need some additional control.
Just some thoughts.
Regards,

But sir in your first link rs485 repeater but in rf signal how can I use repeater of rs485?
Can I use rf booster or repeater ?
Does rf booster boost multiple zigbee's signal at different end or one booster only boost single rf signal please guide me

http://www.synetcom.com/plc wireless ethernet 900 mhz radio.htm

This would hook directly into the RS485 and take the place of the ZigBees (unless you need the ZigBees for something else).

How well it works, or how well any other wireless connection works, for that matter, depends on line of sight. Do you have a clear view of the remote site from your location?