Nordic has been using this type of antenna shape with good success for a long time, but we have not done any radiation pattern measurement on the specific PCA10001 implementation. The radiation patter will change from design to design based on size and shape of ground plane, distance to other metallic objects and housing. We're using this shape as we have good experience with it and that the performance is good. Ideally A straight line would give you a doughnut shaped radiation patter. Once you bend the antenna as we have done to fit it onto our kits you start getting a more complex radiation pattern.
