Most antennas have very little response to Vertical Polarization, hence Total Gain = Horizontal Gain.
Some notable exceptions are RabbitEars (at an angle), Monopole Whips and Loops.
In Dual Vee antenna Total Gain = Horiz. Gain when whiskers point to the sides. When it is
rotated onto it's side (the Hi-VHF example), Total Gain = Vertical Gain. There is very little
cross-polarization (mis-matched) response. BTW: SWR is best (<2.5) matched to 150-ohms.
Preparing for deployment of ATSC-M/H (Mobile, Handheld) waveform, more and more stations
are adding another transmitter and antenna in order to transmit both Horiz. and Vertical...
either EP (Elliptical Polarization) or CP (Circular Polarization) when equal power.
In the U.S., they are permitted to transmit the SAME power in Vert. as current Horiz.
Fol. website maintains a Spread Sheet showing EP/CP status for U.S. stations:
Even if a station is still transmitting Horiz. (only) at the receiver, signficant power may also be
present in the Vert. Polarization....due to reflections. Indoor RabbitEars have exploited this crude
Polarization Diversity for many years.....