You can try this antenna: QUICK SPIDER - No Soldering, No Connector
But it’s not gonna be that much better than a half-wave dipole.
The half-wave dipole should be 144 mm or 6.06 in from end to end for best reception.
Reception of an outdoor antenna is generally much better, more difference than antenna type.
But range on 978 MHz is limited due to the low level of the aircraft operating those transponders.