Powerline Essentials Edition 1010 Model PLW1010 and PL1010

I have a Powerline Essentials Edition 1010 consisting of 2 'adapters' identified as 'PLW1010' (has antennas) and 'PL1010' (I'm calling a 'base unit' which is co-located with my home router).  I am trying to add another wireless 'adapter' to a weak signal area in my home and do not understand which component I must purchase.  I am assuming that it might be the PLW1010 with the antennas on it but the guidance on the website is rather confusing.  What is it that I need to purchase to be compatible with my PL1010 'base unit'?