User's Manual

L811-EA Module Hardware User Manual Page
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7.1.2 Impedance
The impedance of the RF signal line needs to be controlled at 50 Ohm.
7.2 Antenna Design
7.2.1 Main Antenna Design Requirements
(1) Antenna efficiency
Antenna efficiency is the ratio of the input power and radiant power. Because of the return loss, material
loss and coupling loss of the antenna, the radiant power is always lower than the input power. The ratio is
recommended to be controlled over 40% (–4dB).
(2) S11 or VSWR
S11 indicates the matching level of the 50 Ohm impedance for the antenna. It affects the antenna
efficiency in a certain extent. The VSWR testing method could be used for measuring purposes. The
recommended value for S11 is less than –10dB.
(3) Polarization
Polarization refers to the rotation direction of electric field while the antenna is in the direction of maximum
radiation. Linear polarization is recommended. It is recommended to use the diversity antenna which has
the different polarization direction from the main antenna.
(4) Radiation pattern
The radiation pattern refers to the intensity of the electromagnetic field while the antenna is in every
direction of the far field. Dipole antenna is perfect as the terminal antenna. For built-in antenna, it is
recommended to use PIFA or IFA antennas.

Antenna dimension: 6mm * 10mm * 100mm (H*W*L).
 Antenna radiation direction: Omnidirectional.
(5) Gain and directivity
Antenna directivity refers to the intensity of the electromagnetic field while the electromagnetic wave is in
all directions. Gain is the collection of of the efficiency and directivity of the antenna. It is recommended
that antenna gain is less than or equal to 3dBi.
(6) Interference
In addition to antenna performance, some other interference from the PCB will also affect the module
performance. To ensure the high performance of the module, the interference must be under control.
Suggestions: Keep speaker, LCD, CPU, FPC wire routing, audio circuits, and power supply away from the