  The 4--8 GHz FR1(C) and 7--24 GHz upper mid-band FR3 spectrum are promising
new 6G spectrum allocations being considered by the International
Telecommunications Union (ITU) and major governments around the world. There is
an urgent need to understand the propagation behavior and radio coverage,
outage, and material penetration for the global mobile wireless industry in
both indoor and outdoor environments in these emerging frequency bands. This
work presents measurements and models that describe the penetration loss in
co-polarized and cross-polarized antenna configurations, exhibited by common
materials found inside buildings and on building perimeters, including
concrete, low-emissivity glass, wood, doors, drywall, and whiteboard at 6.75
GHz and 16.95 GHz. Measurement results show consistent lower penetration loss
at 6.75 GHz compared to 16.95 GHz for all ten materials measured for co and
cross-polarized antennas at incidence. For instance, the low-emissivity glass
wall presents 33.7 dB loss at 6.75 GHz, while presenting 42.3 dB loss at 16.95
GHz. Penetration loss at these frequencies is contrasted with measurements at
sub-6 GHz, mmWave and sub-THz frequencies along with 3GPP material penetration
loss models. The results provide critical knowledge for future 5G and 6G
cellular system deployments as well as refinements for the 3GPP material
penetration models.
