Do I need to replace WiFi antennas in my laptop when upgrading the WiFi module?

I have a Packard Bell EasyNote LM85 laptop that comes with an Atheros AR5B95 WiFi module (mini-PCIe, 1x1, marketed as 802.11n (actually b/g for all practical purposes, maximum connection speed 54Mbps), 2.4GHz, two antenna wires, no Bluetooth). No Bluetooth in other parts of the laptop either.

I wanted to replace it with an 802.11ac module, so I purchased an Intel 7260HMW.AC, which is the latest module still in the mini-PCIe form factor. That module is a 2x2, 2.4 + 5 GHz, and has integrated Bluetooth 4.0. It has two connectors for the antennas, just like my old module.

However with the new module the laptop drops out of the network every minute or so. It reconnects very quickly, but it is still pretty annoying. It would first connect at 887 Mbps, then gradually drop to lower and lower speeds over the course of the minute, then drop out completely, then reconnect at 887Mbps and repeat.

I am considering looking into replacing the original antennas with ones that come with the module, but what bothers me is that they look like simple wires, and the connectors on the old and new WiFi modules look identical and have the same number of contacts. Does it make sense to replace the antennas too, are they "devices" that have some internal setup that needs to match the radio module, and is it even feasible to replace them?

It looks like your old card was 2.4GHz-only, so your laptop's built-in antennas are probably "single band"; that is, they are only optimized for 2.4GHz, and probably perform poorly at 5GHz. 802.11ac is a 5GHz-only technology, so your new 802.11ac card will not do well with single-band 2.4GHz-only antennas.

If you have a way to replace the antennas in your laptop, you will want to replace them with dual-band antennas (ones that are designed to perform well in both the 2.4GHz and 5GHz bands).