 Hi, I'm Thomas with Archive Elements. Today we'll talk about front-to-back ratio. Before that, if you find our videos useful, like, comment, and consider subscribing to our channel and we'll let you know whenever a new video is out. A major engineering organization defines front-to-back ratio in a following way. It is the ratio of the maximum directivity of an antenna to its directivity in a specified backward direction. Wondering what this means in human language? Let's have a look. Front-to-back ratio says how strong the back loop is compared to the main loop. Even though back loop, as well as any other radiation outside the main loop, is considered a side loop, it got a specific name because it radiates precisely in the opposite direction as the main loop. Once we know the radiation pattern of an antenna, front-to-back ratio is the difference between the gain of the main loop and the gain of the back loop. In the practical life, back loop doesn't necessarily point exactly backwards because of the manufacturing and design imperfections. Therefore, the front-to-back ratio is often defined as the gain of the main loop, minus the gain of the strongest side loop within a plus-minus 30 degree angle around the backward direction. Manufacturers in the Wisp industry often claim that the good front-to-back ratio means an antenna is good for dense collocations. This is simply not true. In reality, back loop is only one out of many side loops antennas used in Wisp industry typically have, making it largely irrelevant. On top of that, the size of the side loops changes with frequency, which degrades the practical value of front-to-back ratio as a measure of the side loop performance even more. In low-interference areas, high-front-to-back ratio is not so important because there is no interference potentially harming a wireless network in the first place. In high-interference areas, front-to-back ratio is also irrelevant. This is because the rest of the side loops still collect the interference, harming a wireless network by increasing the noise floor the radio is working with. The other side loops antennas used in Wisp industry usually have completely diminished the benefit that high-front-to-back ratio supposedly brings. A true measure of side loop performance is beam efficiency. If you want to know more about beam efficiency, check out our previous videos by clicking the link in the corner or in the video description. A good example of antennas with no side loops are RF elements horn sectors optimized for 5 GHz Wisp networks in high-interference and high-customer density areas. If you enjoyed our video, leave us a comment, like and consider subscribing to our channel or check out some of our previous episodes.