  Omni-directional pathloss, which refers to the pathloss when omni-directional
antennas are used at the link ends, are essential for system design and
evaluation. In the millimeter-wave (mm-Wave) and beyond bands, high gain
directional antennas are widely used for channel measurements due to the
significant signal attenuation. Conventional methods for omni-directional
pathloss estimation are based on directional scanning sounding (DSS) system,
i.e., a single directional antenna placed at the center of a rotator capturing
signals from different rotation angles. The omni-directional pathloss is
obtained by either summing up all the powers above the noise level or just
summing up the powers of detected propagation paths. However, both methods are
problematic with relatively wide main beams and high side-lobes provided by the
directional antennas. In this letter, directional antenna based virtual antenna
array (VAA) system is implemented for omni-directional pathloss estimation. The
VAA scheme uses the same measurement system as the DSS, yet it offers high
angular resolution (i.e. narrow main beam) and low side-lobes, which is
essential for achieving accurate multipath detection in the power angular delay
profiles (PADPs) and thereby obtaining accurate omni-directional pathloss. A
measurement campaign was designed and conducted in an indoor corridor at 28-30
GHz to verify the effectiveness of the proposed method.
