  The North Polar Spur (NPS) is a giant structure that is clearly visible in
both radio and X-ray all-sky maps. We analyzed broadband radio observations
covering a range between 22 MHz and 70 GHz to systematically analyze the
thermal/non-thermal emissions associated with the NPS. We demonstrate that the
radio emission of the NPS comprises synchrotron, free-free, and dust emission;
however, synchrotron emissions dominate over other emissions, especially at
high galactic-latitudes. Moreover, the synchrotron spectra exhibit a power-law
behavior with $N(\gamma)\propto\gamma^{-s}$ ($s\simeq1.8-2.4$) up to a few GHz
moderated by a turnover at $\nu_{\rm brk} \simeq 1$ GHz, above which the
spectral index $s$ decrease by one. Assuming that the turnover is due to the
electrons cooled by synchrotron radiation before escaping (or advecting) from
the emission region, the magnetic field strength can be estimated to be $B\sim
8 \rm\mu G$ if the NPS is a distant structure that is near the Galactic Center
(GC). However, an unreasonably strong $B\sim 114\rm\mu G$ is required if the
NPS is near the local supernova remnant (SNR). The corresponding non-thermal
energy stored in the NPS is $E_{\rm n/th}\simeq 4.4\times 10^{55}$ erg in the
GC scenario, whereas $E_{\rm n/th}\simeq 4.1\times 10^{52}$ erg is difficult to
explain with a single local SNR. We also estimated the gamma-ray emission
associated with the NPS through inverse Comptonization of the cosmic microwave
background (CMB), which peaks at 100 - 1000 keV with a flux of $\nu F_{\nu}\sim
10^{-9}$ $\rm erg\,cm^{-2}s^{-1}sr^{-1}$ in the GC model, and may be a good
candidate for detection by future X-ray/gamma-ray observatories.
