What is the front-to-back ratio of the radiation pattern shown in Figure E9-2?

The front-to-back ratio is determined by comparing the maximum forward gain of the antenna (the "front") to the gain exactly 180 degrees opposite to it (the "back"). In Figure E9-2, you must read these values directly from the provided polar plot. The main lobe (front) peaks at the outer edge of the graph, which serves as the 0 dB reference line. When you look precisely 180 degrees away from the main lobe to the back of the antenna, the plot crosses the -28 dB ring on the scale. Since the front is at 0 dB and the rear is at -28 dB, the total difference between the two is 28 dB. This means the front-to-back ratio is 28 dB, demonstrating how effectively this particular antenna rejects signals arriving from the rear.