tandem repeat plasmid?

[Ali Karami]

Dear molbioneters

This is my question :

I am working with linear plasmid when i digest  this plasmid total siz of fragments became twice as size of original plasmid . is iit tandem repeat or dimmer but
i have extracted this plasmid several times from gel .
  
How can i explain this ? and if it is tandem repeat how can i prov that.

i appreciate any comments.

thanks

ali at biobase.aau.dk