Frequency
Data transmission between any two points by electromagnetic waves carry a certain amount of kinetic energy therewith. This associated energy of a wave is directly proportional to the wave's frequency. The formula to calculate that energy is E = h * ν, where ν is the frequency and h is Planck's constant, 6.626 * 10-34 J*s. Therefore, the higher the frequency, the more kinetic energy the wave carries, the more powerful the wave is. Most wireless networking antennas operate at 2.4 GHz and 5.8 GHz frequencies. this is often found in wireless networks (802.11b, 802.11g, 802.11n, and 802.11ac).Gain
Gain measures an antenna's ability to amplify incoming signals. In other words, the gain value directly determines the antenna's receiving strength. Gain is measured in dB (decibels), and is a function of the antenna's capture area and reception/transmission frequency. Larger antennas with greater capture area generally have higher gain values, as do ones operating at higher frequencies. For wide-area networks, where data transmission occur across a long-distance area, you will need an antenna with a high gain rating ( > 10 ). If the data transmission area for the antenna is in a small room, then a lower gain antenna will suffice.Beam Width
Beam width is a measurement of the area over which the antenna receives signal. In most cases, it is measured to the "half-power points," which is the number of degrees between the points where the gain is 3 dB less than the gain for the antenna's strongest direction. Generally, the higher the gain, the smaller the beam width. An antenna with high gain and low beam width receives signals over a smaller area, but receives such signals at a strong strength (longer distance); whereas, an antenna with low gain and high beam width receives signals over a larger area, but at weaker strengths (shorter distance). The beam width measurement for an antenna comes in two planes, the vertical and horizontal plane. When the antenna is physically positioned in the proper "right-side-up" orientation, the horizontal plane is the plane parallel to the ground, and the vertical plane is perpendicular to the horizontal plane. The below labeled pictures will assist you in further understanding of an antenna's beam width. The "A" label represents the vertical (elevation) plane and the "B" label represents the horizontal (azimuth) plane.