In a portal, a circular antenna is often used, since the orientation of the tags
entering the IZ cannot be guaranteed. Ensuring the proper overlap between inward-facing
antennas is also critical to achieve successful reads in the IZ. The
antenna fields should overlap where the tags will most likely travel. Don’t forget
that the width of the antenna is being narrowed as you get closer to the antenna,
as discussed in Chapter 2. Therefore, the antennas should be set up for the
tagged objects to travel at least 1.5 to 2 feet from the face of the antenna. If the
tags were too close to the antenna mounting structure, the width of the IZ
would be so small that the tags could pass outside of the coverage area.