  We present high-pass filtered continuum images of the inner
$3.5^\circ\times2.5^\circ$ of the Galactic center at 20 cm with $6.4''$
resolution. These mosaic images are taken with MeerKAT and reveal a large
number of narrow filaments, roughly an order of magnitude increase in their
numbers compared to past measurements. For the first time, we carry out
population studies of the spectral index and magnetic field of the entire
region. The mean spectral indices of the filaments are steeper than supernova
remnants (SNRs) (-0.62) with a value of $\alpha\sim-0.83$. The variation in
$\alpha$ is much larger than for the SNRs, suggesting that these
characteristics have a different origin. A large-scale cosmic-ray driven wind
has recently been proposed to explain the origin of filaments and the
large-scale 430 pc bipolar radio and X-ray structure. This favors the
possibility that the large-scale bipolar radio/X-ray structure is produced by
past activity of Sgr A* rather than coordinated burst of supernovae. A trend of
steeper indices is also noted with increasing distance from the Galactic plane.
This could be explained either by synchrotron cooling or weak shocks
accelerating cosmic-ray particles in the context of the cosmic-ray driven wind.
The mean magnetic field strengths along the filaments ranges from $\sim100$ to
400 $\mu$G depending on the assumed ratio of cosmic-ray protons to electrons.
Given that there is a high cosmic ray pressure in the Galactic center, the
large equipartition magnetic field implies that the magnetic field is weak in
most of the interstellar volume of the Galactic center.
