Portable Host Device Simultaneous Transmission Regulatory SAR Evaluation Procedures
Simultaneous transmission SAR evaluation demands spatial ratio summation, proximity sensor backoff calibration, and time-averaged power tracking across radios.
Sub-6 GHz SAR
Meaning
Radio frequency absorption testing represents the evaluation of electromagnetic energy deposited in biological tissue from transmitters operating below 6 GHz. In this frequency range, sub-6 ghz sar is the primary compliance metric used to verify that devices such as LTE and sub-6 GHz 5G smartphones do not exceed regulatory exposure limits. The evaluation uses liquid-filled phantoms to simulate human tissue because these frequencies penetrate several centimeters into the body.
This testing is mandatory for all mobile products operating in these bands, and it differs from the power density measurements used at higher frequencies.
Measurement Setup
Testing requires placing the device in various positions against a phantom containing tissue-simulating liquid. A robotic arm moves a probe through the liquid to measure the electric field, which determines the sub-6 ghz sar distribution. The device transmits at its maximum power during this test.
The process is conducted in a shielded anechoic chamber.
Antenna Influence
The physical placement of the antennas within the device chassis directly influences the sub-6 ghz sar value. Multiband designs require multiple antennas, which can create complex exposure profiles when operating simultaneously. Engineers adjust the antenna feed lines and matching networks to shape the radiation pattern.
This optimization helps keep exposure within limits.
Exposure Mitigation
When a device struggles to meet limits, designers use conducted power reduction algorithms. These algorithms lower the maximum transmit power when proximity sensors detect a user, which reduces the sub-6 ghz sar to acceptable levels. This reduction is activated automatically.
It ensures continuous safety.