JODY-W2 - System integration manual
UBX-18068879 - R14
Design-in
Page 23 of 84
C1 - Public
Antenna design
Designers must take care of the antennas from all perspective at the very start of the design phase
when the physical dimensions of the application board are under analysis/decision, since the RF
compliance of the device integrating JODY-W2 module with all the applicable required certification
schemes heavily depends on antennas radiating performance.
•
External antennas such as linear monopole:
o
External antennas basically do not imply physical restriction to the design of the PCB where
the module is mounted.
o
The radiation performance mainly depends on the antennas. It is required to select antennas
with optimal radiating performance in the operating bands.
o
RF cables should be carefully selected with minimum insertion losses. Additional insertion loss
will be introduced by low quality or long cable. Large insertion loss reduces radiation
performance.
o
A high quality 50
coaxial connector provides proper PCB-to-RF-cable transition.
•
Integrated antennas such as patch-like antennas:
o
Internal integrated antennas imply physical restriction to the PCB design:
▪
Integrated antenna excites RF currents on its counterpoise, typically the PCB ground plane
of the device that becomes part of the antenna; its dimension defines the minimum
frequency that can be radiated. Therefore, the ground plane can be reduced down to a
minimum size that should be similar to the quarter of the wavelength of the minimum
frequency that has to be radiated, given that the orientation of the ground plane related to
the antenna element must be considered.
▪
The RF isolation between antennas in the system must be as high as possible and the
correlation between the 3D radiation patterns of the two antennas has to be as low as
possible.
▪
In general, an RF separation of at least a quarter wavelength between the two antennas is
required to achieve a minimum isolation and low pattern correlation; increased separation
should be considered, if possible, to maximize the performance and fulfil the requirements
in
▪
A numerical example for estimating the physical restrictions on a PCB is given here:
Frequency = 2.4 GHz
→
Wavelength = 12.5 cm
→
Quarter wavelength = 3.5 cm
o
Radiation performance depends on the whole product and antenna system design, including
product mechanical design and usage. Antennas should be selected with optimal radiating
performance in the operating bands according to the mechanical specifications of the PCB and
the whole product.
