TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R28
Design-in
Page 86 of 164
2.4
Antenna interface
TOBY-L2 and MPCI-L2 series modules provide two RF interfaces for connecting external antennas:
ANT1 represents the primary RF input/output for LTE/3G/2G RF signal transmission and reception
ANT2 represents the secondary RF input for LTE MIMO 2 x 2 or 3G Rx diversity RF signal reception
Both the ANT1 and the ANT2 pins have a nominal characteristic impedance of 50
and must be
connected to the related antenna through a 50
transmission line to allow proper transmission /
reception of RF signals.
☞
Two antennas (one connected to ANT1 pin and one connected to ANT2 pin) must be used to
support the Down-Link MIMO 2 x 2 radio technology. This is a required feature for LTE category 4
User Equipments (up to 150 Mb/s Down-Link data rate) according to 3GPP specifications.
2.4.1
Antenna RF interfaces (ANT1 / ANT2)
2.4.1.1
General guidelines for antenna selection and design
The antenna is the most critical component to be evaluated. 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
TOBY-L2 and MPCI-L2 series modules with all the applicable required certification schemes depends
on antennas radiating performance.
LTE/3G/2G antennas are typically available in the types of linear monopole or PCB antennas such as
patches or ceramic SMT elements.
External antennas (e.g. linear monopole)
o
External antennas basically do not imply physical restriction to the design of the PCB where
the TOBY-L2 and MPCI-L2 series 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 to have minimum insertion losses. Additional insertion
loss will be introduced by low quality or long cable. Large insertion loss reduces both transmit
and receive radiation performance.
o
A high quality 50
RF connector provides proper PCB-to-RF-cable transition. It is
recommended to strictly follow the layout and cable termination guidelines provided by the
connector manufacturer.
Integrated antennas (e.g. patch-like antennas):
o
Internal integrated antennas imply physical restriction to the design of the PCB:
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 relative to the antenna element must
be considered.
The isolation between the primary and the secondary antennas 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, a separation of at least a quarter wavelength between the two antennas
is required to achieve a good isolation and low pattern correlation.
As numerical example, the physical restriction to the PCB design can be seen as following:
Frequency = 750 MHz
Wavelength = 40 cm
Minimum GND plane size = 10 cm
