Antenna to Antenna Isolation

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Antenna to antenna isolation is a measure of how tightly coupled antennas are. Typically, antenna isolation is measured for antennas on the same product - that is, the isolation between a smartphone gps and wifi antenna, for instance. When specified in this manner, the isolation should be as large as possible.

Isolation between a GPS and WIFI antenna that are near each other will be on the order of 20-30 dB, with higher values being preferred. The method of measuring isolation is typically done by connecting both antennas to a Vector Network Analyzer, and measuring S12 (the transmission coefficient).

For antennas that share a common ground plane, such as the diversity and primary cellular antennas on a smartphone, the isolation can be as low as -10 dB or less at the lowband. This will cause a loss in both antenna's efficiency.

Antenna to antenna isolation can be increased by:

  • Increasing the physical separation between the antennas
  • Using different polarizations for the antennas in question
  • If the antennas have different frequencies, using filters to reduce efficiency at the opposite antenna's frequency
  • Reducing the correlation coefficient between the antenna's radiation patterns - that is, have the antenna's peak radiation in different or opposite directions

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