  We present a novel design of loop-gap resonator, the loop-zag resonator, for
sub-X-band electron-spin resonance spectroscopy. The loop-zag design can
achieve improved coupling to small-sample spin systems through the improvement
of sample filling factor and RF $B_1$ field. By introducing ``zags'' to the
resonator's gap path, the capacitance is increased, accommodating a smaller
loop size and thereby a larger filling factor to maintain the requisite
resonant frequency. We present experimental spectra on five different
resonators, each with approximately the same resonant frequency of
$\sim2.9$~GHz, showing that an increase in the number of zags and reduction in
loop size gives rise to higher sensitivity. Finite-element simulations of these
resonators provide estimates of the improved filling factors obtained through
the addition of zags. The frequency range over which this loop-zag design is
practical enables a breadth of future applications in microwave engineering,
including ESR and ESR-like quantum information microwave techniques.
