LoRaWAN Antenna Measurement(SWR and Frequency Plot)

1. The antenna available for LoRaWAN are typically ruby ducky/whip, ground plane and fiber glass
antenna. We decided to measure the SWRs using low cost network analyzer with
SWR.NWT4000-1 138MHz-4.4GHz Sweeper, Spectrum, Source, Network analyzer (you could fine
the instrument in aliexpress.com, ebay.com and taobao.com) is a good choice to find SWRs
when it is difficult to afford a Vector network analyzer.
A SWR bridge (a special type directional coupler) is used in this experiment. One could purchase
such SWR bridge from aliexpress.com/ ebay.com/taobao.com.
The antenna available for LoRaWAN are typically ruby ducky/whip, ground plane and fiber glass
antenna.We decided to measure the SWRs using low cost network analyzer with SWR.NWT4000-
1 138MHz-4.4GHz Sweeper, Spectrum, Source, Network analyzer (you could fine the instrument
in aliexpress.com, ebay.com and taobao.com) is a good choice to find SWRs when it is difficult to
afford a Vector network analyzer.
A SWR bridge (a special type directional coupler) is used in this experiment. One could purchase
such SWR bridge from aliexpress.com/ ebay.com/taobao.Specification of SWR Bridge
SWR Bridge:
- Impedance: 50 Ohm
- Directivity: >30dB
- Frequency range: 2MHz-1500MHz
- Insertion Loss: 13dB
Specification of NWT4000-1(Spectrum/Network Analyzer)
Specifications:
- Model: NWT4000
- Frequency Range: 138MHz-4.4GHz (without interruption), stepping 1kHz
- RF Output power: -5dBm
- Maximum input signal strength: -5dBm
- Scan speed: 4 seconds 550 points
- Interface: USB, SMA
- Power Supply: DC12V / 0.5A
- Size: 118 * 64.5 * 23.5mm
- Weight: about 300 grams with all accessories

2. NWT4000-1 connection to SWR Bridge
The Output of NWT4000-1 is connected RF IN of SWR bridge, the input of NWT4000-1 is
connected to RF OUT of the SWR bridge and DUT (Device under test) is connected to antenna
connector.
The spectrum analyzer software could be downloaded from http://www.dl4jal.eu/
OUT
DUT
Antenna
IN
NWT4000-1
Network Analyzer
RF OUT
RF IN
SWR Bridge

3. Rubber ducky Antenna ,210 mm
Lowest SWR 1.3 happens at 888 Mhz . At 868 MHz, SWR is around 1.98
Rubber ducky Antenna ,110 mm

4. Rubber ducky Antenna ,210 mm

5. Specification
Electrical specifications
Frequency Range(MHz) 868
Impedance(ohm) 50
Gain (dBi) 5.0
Polarization Vertical
Radiation Omni
VSWR <1.7
Maximum input power (W) 50
Mechanical specifications
Connector SMA-Male
Height 210mm
Radome Material Polyurethane
Color White
Operating temperature (℃) -40～70

7. Ground Plane antenna
Electrical specifications
Frequency Range(MHz) 868
Polarization Vertical
Gain (dBi) 3.0
Radiation Omni
VSWR ≤1.5
Maximum input power (W) 50
Lighting Protection Direct Ground

8. Mechanical specifications
Connector TNC (or according to customer)
Dimension (mm) Ø115×225 mm
Length of Cable(m) 3.0
Reflector material Stainless steel
Operating temperature (℃) -50～70

9. Another DIY way to calculate SWR
In this method, we used RTL SDR, Wide band Noise Generator and SWR Bridge. The signal is provider
by wideband noise generator and return power is received by the RTL SDR.
Equipment
 Noise Source/Tracking Generator
 10-12V Power Supply
 RTL-SDR Dongle(From RTL-SDR Blog)
 SWR Bridge (20-23$)
 Directional Coupler 20dB or 10dB (3$)
Software
We used rtl_power with the RTL-SDR Panorama (http://sourceforge.net/projects/guiforrtlpower/ )
GUI to record and graph a frequency sweep over the effective range of the antenna.
The SWR calculation is carried out by referring to excel sheet provided in https://www.rtl-
sdr.com/rtl-sdr-tutorial-measuring-filter-characteristics-and-antenna-vswr-with-an-rtl-sdr-and-noise-
source/
OUT
DUT
Antenna
IN
Noise Generator
RF OUT
RF IN
SWR Bridge
RTL Software
Defined Radio

10.  Scan the complete range without connecting the antenna and measure the return loss.
 Scan the complete range connecting the antenna and measure the return loss.

11. Directional Coupler as SWR Bridge
Specification of Directional Coupler
 Specification Frequency Range (MHz) 698 - 2700
 Coupling(db) 20
 Insertion Loss(dB) ≤0.15
 In-Band Ripple ≤0.3
 VSWR ≤1.3
 Impedance 50 Ohms
 IMD (dBc) ≤-140 @ +43dBm×2
 Connectors N –Female
 Power Handling (Watts) 200 Peak Power(W) 1000
 Temperature (℃) -35 to +70
 Humidity 95%
 Environmental Specs indoor
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750000000 800000000 850000000 900000000 950000000 1E+09
SWR
Freq(Hz)
SWR
OUT
Input
Port
Antenna
IN
Noise Generator
Coupling Port
Output Port
Directional Coupler
RTL Software
Defined Radio

12. Directional Coupler Output Port: Noise Generator/Tracking Generator
Directional Coupler Input Port: Antenna
Directional Coupler Coupling Port: RTL SDR Receiver

13. 0
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750000000 800000000 850000000 900000000
SWR
Freq(Hz)
SWR