Ublox JODY-W1 Series System Integration Manual page 24

• Integrated antennas such as patch-like antennas:
Internal integrated antennas imply physical restriction to the PCB design:
o
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 has to 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
Table 18.
Find below a numerical example to estimate the physical restrictions on a PCB:
Frequency = 2.4 GHz → Wavelength = 12.5 cm → Quarter wavelength = 3.125 cm
Radiation performance depends on the whole product and antenna system design, including
o
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.
Table 17 summarizes the requirements for the antenna RF interface while
additional requirements for dual antenna design implementation.
Item Requirements
Impedance 50  nominal characteristic
impedance
Frequency Range 2400 – 2500 MHz
5150 – 5850 MHz
Return Loss
S
recommended
S
acceptable
Efficiency
> -1.5 dB ( > 70% )
recommended
> -3.0 dB ( > 50% ) acceptable
Maximum Gain
Table 17: Summary of antenna interface requirements
Item Requirements
Isolation S
21
(in-band)
Isolation S
21
(out-of-band) S
21
UBX-16012621 - R18
C1-Public
< -10 dB (VSWR < 2:1)
11
< -6 dB (VSWR < 3:1)
11
> 30 dB recommended
> 35 dB recommended
> 30 dB acceptable
JODY-W1 series - System integration manual
Remarks
The impedance of the antenna RF connection must match the 50 
impedance of Antenna pins.
For 802.11b/g/n and Bluetooth.
For 802.11a/n/ac.
The return loss or the S
11
reflected power, measuring how well the primary antenna RF
connection matches the 50  characteristic impedance of antenna
pins. The impedance of the antenna termination must match as
much as possible the 50  nominal impedance of antenna pins over
the operating frequency range, to maximize the amount of power
transferred to the antenna.
The radiation efficiency is the ratio of the radiated power to the
power delivered to antenna input: the efficiency is a measure of how
well an antenna receives or transmits.
The maximum antenna gain must not exceed the value specified in
type approval documentation to comply with regulatory agencies
radiation exposure limits.
Remarks
The antenna-to-antenna isolation is the S
the two antennas in the band of operation.
Lower isolation might be acceptable depending on use-case
scenario and performance requirements.
Out-of-band isolation is evaluated in the band of the aggressor to
ensure that the transmitting signal from the other radio is
sufficiently attenuated by the receiving antenna to avoid
saturation and intermodulation effect at the receiver's port.
Design-in
Table 18
, as the VSWR, refers to the amount of
parameter between
21
specifies
Page 24 of 72