What is Antenna Pattern?
Here I write about antenna pattern, Front-to-rear Ratio and Upper Side Lobe Suppression in antenna.
The pattern is the electromagnetic field of antenna radiation distributed by coordinate along fixed distance.
- If the pattern is represented by radiation field strength, it is called field strength pattern.
- If the pattern is represented by power density, it is called power pattern.
- If the pattern is represented by phase, it is called phase pattern.
In mobile communication, the power pattern is the most common.
The antenna pattern is a cubic figure, usually represented by two patterns which are vertical to each other in a main plane. This is the surface pattern. The surface pattern includes vertical pattern and horizontal pattern. There are also omnidirectional antenna pattern and directional antenna pattern. There are other special directional antennas, such as heart-shaped antenna and 8-shaped antenna.
The directionality of antenna lies in the ranking of oscillators and the variety of feeder phase, similar to the interferometric effect of optics in principium. As a result, the power in some directions is strengthened while the power in some directions is weakened. The lobes of various shapes and zero points form. The lobe with the highest power is the main lobe. The lobes near the main lobe with the second highest power are the first side lobes. The second side lobes are those with the third highest power. The directional antenna produces a rear lobe. Figure shows the horizontal and vertical patterns of directional antenna.
It is the ratio of signal radiation strength of main lobe to that of rear lobe, the difference between the level of side lobe and the maximum beam in the range of rear 180°±30°, a positive value. The front-to-rear ratio of common antennas is between 18 dB and 45 dB.
Upper Side Lobe Suppression
In a cellular network, to improve the efficiency of frequency reuse and reduce the intra-frequency interference with neighbor cells, for shaped-beam antenna, you need lower the upper side lobe that radiates neighbor cells and improve the D/U ratio (the ratio of strength of useful signal to that of interference signal). The level of the first upper side lobe compared with main lobe shall be smaller than –18 dB. This is invalid to the antennas of macro cell eNodeB.