Antenna and balun for MRF49XA
If you read quickly the datasheet (page 73), you'll see that you have to use a balun circuit in order to match the IC's pins high input impedances to the antenna's impedance which is likely to be 50 \$\Omega\$

If you go further and read page 13 :


  The LNA has approximately 250 \$\Omega\$ of differential input
  impedance which functions well with the proposed antenna 
  (PCB/Monopole)  during  signal transmission. The LNA, when connected
  to the 50 \$\Omega\$ device, needs an external matching circuit
  (Balun) for correct matching and to minimize the noise figure of the
  receiver.


So you definitely need a 50 \$\Omega\$ unbalanced to 250 \$\Omega\$ differential impedance matching circuit, the technology you want to use is up to you.

In RF electronics, impedance matching between interconnected circuits is mandatory, should it be for signal integrity reasons or hardware safety reasons.