  We present an S-band tunable loop gap resonator (LGR) providing strong,
homogeneous, and directionally uniform broadband microwave (MW) drive for
nitrogen-vacancy (NV) ensembles. With 42 dBm of input power, the composite
device provides drive field amplitudes approaching 5 G over a circular area
$\gtrsim\!50$ mm$^2$ or cylindrical volume $\gtrsim\!250$ mm$^3$. The wide 80
MHz device bandwidth allows driving all eight NV Zeeman resonances for bias
magnetic fields below 20 G. For pulsed applications the device realizes
percent-scale microwave drive inhomogeneity; we measure a fractional
root-mean-square inhomogeneity $\sigma_\text{rms}\!=\! 1.6\%$ and a
peak-to-peak variation $\sigma_\text{pp}\!=\! 3\%$ over a circular area of 11
mm$^2$, and $\sigma_\text{rms} \!=\! 3.2\%$ and $\sigma_\text{pp}\! =\! 10.5\%$
over a larger 32 mm$^2$ circular area. We demonstrate incident MW power
coupling to the LGR using multiple methodologies: a PCB-fabricated exciter
antenna for deployed compact bulk sensors and an inductive coupling coil
suitable for microscope-style imaging. The inductive coupling coil allows for
approximately $2\pi$ steradian combined optical access above and below the
device, ideal for envisioned and existing NV imaging and bulk sensing
applications.
