Diversity Gain Measurements
A reverberation chamber simulates a uniform multipath environment when the modes are stirred. Diversity antennas will be used to improve performance of future mobile communication systems.
The reverberation chamber is the only laboratory equipment that can measure diversity gain. The alternative is to drive the measurement equipment around in a real multipath environment, such as a in a city.
The measurement setup in the Bluetest RC800 chamber is shown in the drawing. The simulated multipath environment is repeatable, so we can measure the two antenna branches one after the other.
We can measure diversity gain relative to different single antenna references. The apparent diversity gain is measured relative to one of the branches. A more practical effective diversity gain is measured relative to an ideal reference antenna, which is lossless and matched to 50 Ohms. The actual diversity gain is measured relative to an existing single-antenna solution, with a certain radiation efficiency.
Definition formulas of the different diversity gains (SNR=signal-to-noise ratio):
Bluetest RC800 reverberation chamber and setup for diversity measurements. The field is stirred by 2 mechanical stirrers, a platform stirrer, polarization stirring and frequency stirring.
Example of simple two-dipole diversity antenna located 2 cm from a cylinder filled with tissue-equivalent liquid. Results are given below.
Diversity gains by selection combining at 1% cumulative probability level. The actual diversity gain is measured relative to a single dipole located the same 2 cm distance from the cylinder. 900 MHz.
Example of statistics of measured signal levels at 900 MHz.
