Reducing system voltage whilst getting the same output from a PCB antenna
First of all, it isn't the resistors that are limiting the current out of the gates &mdash; the AC impedance of the capacitors at 5 MHz is more than enough for that.

A more important function of the resistors is to isolate the resonant tank circuit from the low output impedance of the gates, allowing the Q of the circuit to be higher than it would be without them.

If anything, I would be tempted to raise the values of the resistors, to maybe 150&Omega; or 220&Omega;, to provide a better match to the antenna.

Otherwise, if you want to redesign the antenna to work at a lower voltage and higher current, you're going to have to reduce the inductance and raise the capacitances by the same ratio in order to keep the same resonant frequency.

This type of antenna only interacts directly with the magnetic field of an EM wave, so its "power" is directly related to the magnetic field it can produce, which is a function of the current through the inductor and the number of turns in it (Ampere-turns).

Since inductance is proportional to N2, halving the number of turns allows roughly 4&times; the current to flow for a given voltage, which gives a net 2&times; improvement in the overall Ampere-turns value. This is an extreme example that shows the principle &mdash; in practice, you'll probably want to make a smaller adjustment to your present design, and you do still need to pay attention to the amount of current the gates can supply.