What is the front-to-back ratio of the radiation pattern shown in Figure E92?

Explication

The radial scale of this elevation plot is marked 0, −10, −20, −30 and −40 dB from the outer ring inward, and the lowest of the four forward lobes reaches the outer 0 dB ring. Behind the antenna, beyond 90 degrees, the response collapses to small lobes near the center that trace to about 29 dB below that peak, and 28 dB is the nearest of the offered values.