with high gain. In other words, the radiation patterns will generally not have directions where the gain exceeds +3 dBi and will also not have directions with very little radiation. The radiation patterns will be generally omni-directional because high-gain, and the narrow radiation lobes of associated with high-gain, require electrically large structures to form array-like antenna structures. Of course, there will be nulls in the radiation patterns in various directions but the nulls will usually be polarization dependent. If a null exists in a particular polarization, it will not exist in the orthogonal polarization.
Figure 3 below shows a typical embedded antenna radiation pattern. The three traces are antenna gain in vertical and horizontal polarization (in dB relative to an isotropic radiator, or dBi) and vertical plus horizontal (the total gain). While this pattern would not normally be considered “omni”, it is acceptable from a gain and overall coverage perspective. It must also be understood that the radiation pattern shown below is just one “slice” from the three dimensional sphere surrounding any device. The features of the pattern (nulls, polarization, maximum gain) will often change dramatically with the angle in what is conventionally called the “pattern cut”.
Figure 3 . Typical Embedded Antenna Radiation Pattern
Antenna Fundamentals – Technical Brief