User's Guide

LM940 HW Design Guide
1VV0301352 Rev. 2 Page 46 of 68 2017-07-19
The second Rx antenna should not be located in the close vicinity of main antenna. In
order to improve Diversity Gain, Isolation and reduce mutual interaction, the two antennas
should be located at the maximum reciprocal distance possible, taking into consideration
the available space into the application. For the same reason, the Rx antenna should also
be cross-polarized with respect to the main antenna.
Isolation between main antenna and Rx antenna must be at least 10 dB in all uplink
frequency bands.
Envelope Correlation Coefficient (ECC) value should be as close as possible to zero, for
best diversity performance. ECC values below 0.5 on all frequency bands are
recommended.
GNSS Receiver
The LM940 integrates a GNSS receiver that could be used in Standalone mode and in A-
GPS (assisted GPS), according to the different configurations.
LM940 supports an active antenna.
Frequency range • Wide-band GNSS:
1560–1606 MHz recommended
• Narrow-band GPS:
1575.42 MHz ± 2 MHz minimum
• Narrow-band Galileo:
1575.42 MHz ± 2 MHz minimum
• Narrow-band BeiDou:
1561.098 MHz ± 2 MHz minimum
• Narrow-band GLONASS:
1601.72 MHz ± 4.2 MHz minimum.
Gain 1.5 dBi < Gain < 3 dBi
Impedance 50 Ohm
Amplification 18 dB < Gain < 21 dB
Supply Voltage 3.1 V
Current consumption 20 mA Typical
7.4.1. GNSS RF Front End Design
The LM940 contains an integrated LNA and pre-select SAW filter.
This allows the module to work well with a passive GNSS antenna. If the antenna cannot
be located near the LM940, then an active antenna (that is, an antenna with a low noise
amplifier built in) can be used with an external dedicated power supply circuit.
GNSS rescive path uses either the dedicated GNSS connector or the shared AUX
connector.