Broadcasters Look to CP Antennas for Improved M/H Performance

On Wednesday at the NAB Show’s Broadcast Engineering Conference, Kerry Cozad, senior vice president of engineering and technology for Dielectric Communications, presented a paper, “Vertical Polarization for UHF DTV” which detailed research done at Dielectric on the value of circular polarization (CP) compared to vertical or horizontal polarization. Dielectric Engineer John Schadler placed a rotating dipole, representing a cell phone rotating through many positions, in an anechoic chamber with scatters around it. An antenna with vertical, horizontal or circular polarization was used with the test transmitter. John found that when CP was used, the average signal at the dipole improved by 5.8 dB, much more than the 3 dB extra power required to create full CP. I’ll cover this topic in more detail in an upcoming “RF Technology” column.

Kerry also revealed a new Dielectric CP panel antenna in the paper. Dielectric was not displaying the antenna in its booth, but after I saw it I can say it does solve the problem of creating a true CP (or elliptical polarization) broadband antenna while maintaining the axial ratio. Note that Dielectric showed that an antenna that simply combines horizontal and vertical polarized signals, resulting in slant polarization, does not provide the same benefit in increased received signal as a true CP antenna.