Integration Manual

NORA-B1 series - System integration manual
UBX-20027617 - R04 Design-in Page 27 of 61
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4.3.2 Antenna design (NORA-B101 only)
NORA-B101 is suitable for designs where an external antenna is needed due to mechanical
integration or placement of the module, or where a host PCB trace or SMT antenna is required by the
application.
Designers must consider the physical dimensions of the application board at the beginning of the
design phase of the end-product. This is important because the RF compliance of the device
integrating the NORA-B1 module, together with all the required certification schemes, heavily
depends on the radiating performance of the antennas.
Designers are encouraged to consider one of the u-blox suggested antenna part numbers and follow
the layout requirements.
• External antennas, such as a linear monopole:
o External antennas do not impose any physical restrictions on the design of the PCB where
the module is mounted.
o The radiation performance mainly depends on the antennas. It is necessary to select
antennas with optimal radiating performance in the operating bands.
o RF cables that offer minimum insertion loss should be carefully chosen. Unnecessary
insertion losses are introduced by low quality or long cables. Large insertion loss reduces the
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 impose physical restrictions on the PCB design:
An integrated antenna excites RF currents on its counterpoise, typically in the PCB ground
plane of the device that effectively becomes part of the antenna. Consequently, the
dimensions of the ground plane define the minimum frequency that can be radiated. To
optimize radiation, the ground plane can be reduced to a minimum size that should not be
less than a quarter of the wavelength frequency that needs to be radiated. The orientation of
the ground plane in relation 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 must be as low as
possible. An RF separation of at least a quarter wavelength between the two antennas is
generally required to achieve a maximum isolation and low pattern correlation; consider
increasing separation, if possible, to maximize performance and fulfill the requirements in
Table 11.
As a numerical example, consider the following physical restrictions of the PCB:
Frequency = 2.4 GHz → Wavelength = 12.5 cm → Quarter wavelength = 3.125 cm
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o Radiation performance depends on the antenna system design, the mechanical design of the
final product, and the application use case. Antennas should be selected with optimal
radiating performance in the operating bands according to the mechanical specifications of
the PCB and the entire product.
Table 11 summarizes the requirements for the antenna RF interface.
Item
Requirements
Remarks
Impedance
50  nominal characteristic impedance
The impedance of the antenna RF connection must match the
50  impedance of the ANT pin.
Frequency Range
24–0 - 2500 MHz
Bluetooth low energy.
Return Loss
S
11
< -10 dB (VSWR < 2:1) recommended
The Return loss or the S
11
, as the VSWR, refers to the amount
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Wavelength referred to a signal propagating over the air