Toyota Repair: 1999 Tiyota Sienna key-less Entry antenna, receiver antenna, key less entry

Question
I have noticed Key-less entry getting weaker and weaker. Tried inserting brand new batteries in both remotes. My remote works very close to the vehicle. Other remote dose not work at all. My question is where is the receptor antenna located in the van? Is there something that can be done to increase the range/distance for the remote.  

Answer
The receiver antenna is built into the keyless entry ecu,there is no adjustment on the factory installed system, if it's an aftermarket system I would recommend consulting an alarm/keyless entry repair place, check the remotes to see if they have the toyota logo, if so then it's either a factory installed or dealer installed system.