Polarization and Multipath, page 6 part 1

CHRONOLOGY OF POLARIZATION RESEARCH

"...all polarizations are tipped in perpendicular to the conducting surface."

  • THE 1987 CROUCH "FIELD DISTORTER" PAPER

In 1987 engineering consultant Marvin Crouch wrote a paper entitled "FM Broadcasting and Multipath" which added some additional conclusions, but no empirical data, to the debate. Crouch, while stating that hilly terrain presents a tough challenge to the broadcaster, added that, "As to automobile reception of vertically polarized transmissions, remember that a metal-bodied vehicle will receive any polarized signal. This is because the metal body is a field distorter and all polarizations are tipped in perpendicular to the conducting surface. A car antenna receives both polarizations in a circularly polarized field and that could present problem if the reflected signal is predominantly vertically polarized." Crouch concluded that use of diversity receive directional antennas needed to become commonplace.

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Polarization and Multipath, page 6 part 2

CHRONOLOGY OF POLARIZATION RESEARCH

  • THE 1989 SANTOS REPORT

A published EBU report in 1989 reaffirmed earlier IRT reports that horizontal polarization performs better than vertical polarization due to (1) lower diffraction loss and (2) higher loss for diffusely reflected waves in hilly terrain. Directional horizontal and vertical antennas were used in the test and measurements were taken at 31 locations at Nanos, Yugoslavia. Vertical polarization was employed on a 100 kW transmitter. The results for the vertically polarized signal were in general dismal: 24 of the 31 test locations showed higher diffraction 1088 for the vertical signal. In only 6 of the 27 test points in shadow was good stereo reception possible with the vertical transmissions. With horizontal polarization 25 of the 27 locations were capable of receiving good stereo, according to the report

Of significance to noncommercial broadcasters in the U.S., however, was the surprising result that for vertically polarized reception, multipath was worse for mixed polarization transmission in which the horizontal component was larger than the vertical. The report concluded:

It may be stated that vertical or mixed polarization is not to be recommended for high power radio broadcast stations having hilly service areas. On the other hand mixed polarization may be a good choice for low-power stations in flat terrain, since it offers advantages with respect to the characteristics of normal forms of car radio antennas. Neither benefits nor disadvantages should be expected for home reception.

Further tests are expected to be published on the follow-up studies in the near future concentrating on differences in circular and horizontal polarization in hilly terrain.

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"...the surprising result [was] that for vertically polarized reception, multipath was worse for mixed polarization transmission in which the horizontal component was larger than the vertical."

Polarization Primer Table of Contents