Why would a wireless smart card antenna have one larger loop and three smaller loops instead of four similar size loops?

Question

This image is originally from here. I added some annotations. The picture shows an x-ray shot of a smart card with wireless capability (and also a contact pad for direct connection to a terminal).

The antenna is made of four loops of wire laid out in concentric pattern. It's a single piece of wire connected on ends only. One loop goes through the entire perimeter and three other loops only go through the top and the middle of the card.

Antenna totally avoiding the bottom of the card is not a rare thing. This is a popular design which purpose is to allow embossing the text near the card bottom. Antenna could be damaged by the emsossing process so cards where embossing is necessary often have the antenna going through the upper half of card only. Cards where embossing is not required don't need this so they may use antennas which are located along the whole perimeter.

So the two popular designs either have all loops avoiding the card bottom or all loops located along the whole perimeter.

In this card three loops avoid the card bottom but the fourth one does not.

What could be the purpose of such antenna design?

Answer 1

A new antenna technology for dual interface smartcards makes it possible to integrate an antenna into the card body that does not need wired contacts to the chip module (cf. [3, 7, 8]). Instead, the antenna in the card body has a few additional turns around the area where the chip module is embedded (see Fig. 16(c)). This card body antenna inductively couples into a tiny loop antenna that is directly integrated into the chip module (see Fig. 16(b)). This simplifies the card production process as the antenna does not need to be attached (e.g. glued, welded or soldered) to the chip module.

Not much help, but the CA and EA initials may hold meaning...

Evaluation of Contactless Smartcard Antennas (2015)

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Fig. 2 represents the layout of the smart card with the free space available for UHF tag. M1 is depicting the [blue] available space for RFID UHF tag, while M2 is showing the NFC track tracks around the bank card, M3 and M4 are showing the area occupied by the EMV chip and the card embossment the red lines are showing the NFC tag tracks around the bank card, yellow lines are depicting the free available space for RFID UHF tag while, the green coloured hatched area is showing the area occupied by the EMV chip and card embossment. As the UHF tag antenna geometry is dipole so for symmetrical design the rectangular blue hatched area is allocated for UHF tag design with area...

Still unclear to me, but it may be something to do with embossment area.

A Novel Design of UHF RFID Passive Tag Antenna Targeting Smart Cards Limited Area (2018)

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Introductory reading:

https://wikipedia.org/wiki/Contactless_smart_card#Technology

Answer 2

Mostly if the antenna is 2/3 or 1/2 then it may fail the EMV level 1 testing, that's why such full antenna is designed which also complies with emboss area requirements.