To RF System
To Range
Factors affecting RANGE
Prior to starting an RF design a realistic range requirement MUST be established
These are the factors affecting range of customers system:
•
The chosen frequency band of operation
(315MHz/433MHz/868MHz/915MHz/2.4GHz)
•
In which countries shall the end product be sold (RF requirements: FCC, ETSI,
Weak Power Radio etc.)
-
Maximum allowed transmitted power (ERP) for territory
•
RF output power and sensitivity of chosen nRF device
•
Available, suitable antennas with given gain figures
•
Necessary margins (system margin) set to allow for additional losses in air
and surroundings (Buildings and objects)
Can the desired range requirement be achieved or not?
The importance of these factors can be shown in the Line-Of-Sight (LOS)
link budget
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Range- Theoretical LOS link budget
The parameters included in LOS link budget calculations are:
•
Allowed transmitter output power (POUT)
•
Transmitter antenna matching network losses (LM_TX)
•
Transmitter antenna gain (Gant_TX)
•
Free space loss (LP), given by frequency of operation and distance
•
Receiver antenna gain (Gant_RX)
•
Receiver antenna matching network losses (LM_RX)
•
Receiver sensitivity (S)
Line-Of-Sight range
(R)
POUT
Path loss (LP)
Antenna
matching
network
Antenna
TX
matching
network
Gant_TX
LM_TX
RX
Gant_RX
LM_RX
Sensitivity (S)
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Range- External losses
For a complete (realistic) range calculation, additional external factors must be
considered:
•
Signal losses caused by objects in the path between the transmitter and receiver
antennas (e.g. walls, floors, furniture, windows)
These losses increases with increasing frequency
•
Range variations caused by multi-path fading
•
Objects in close proximity to the antenna that
affects antenna performance, e.g.:
•
Printed circuit board (PCB)
-
Enclosure, enclosure material
-
Human body
ra
ng
e
2a
rang
e2
b
Obstacle
Pout
range1
TX
RX
Obstacle
-
conducting surface
Quality of sampling, detection and processing of received data from the RF device
These external losses must be added to the LOS link budget for realistic
calculation!
Rule of thumb:
OUTDOOR RANGE = 1/2 of theoretical LOS link range
INDOOR RANGE (trough walls) = 1/10 of theoretical LOS link range
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To RF System
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An example on how to achieve long and reliable range
N5
N6
N3
N1
B
N7
N5
N4
N3
N2
N1
This solution implies:
N6
N7
N4
B
N2
This solution implies:
•
Coverage to/from base station
from/to all nodes
•
Coverage only between
neighbouring nodes
•
Big, high gain antennas
•
Small, low gain antennas
•
High output power
•
Low output power
•
Big and bulky radio devices
•
Small, light weight devices
•
High current consumption
•
Low current consumption
•
Jamming of other systems
•
Low interference
•
Compliance with frequency
regulations?
•
Easy to comply with frequency
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regulations
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Link budget calculation example
System specification:
Frequency of operation (f0)
: 433.92MHz (wavelength =0.69m)
Wanted outdoor range (R)
: 75m  Design for LOS = 2 • R = 2 • 75m = 150m
Transmitter output power (Pout)
: 10dBm
Transmitter antenna gain (Gant_TX): -27dB (18x10mm loop antenna)
Receiver antenna gain (Gant_RX)
: To be decided
Receiver sensitivity (S)
: -105dBm
Line-Of-Sight range
Path loss (L)
TX
Pout
RX
STR-1
STR-2/STR-3
STR-1/STR-3
Gant_TX
Gant_RX
Sensitivity (S)
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Link budget calculation example
Calculation 1:
Can the 150m line-of-sight range requirement be achieved with a 25x15mm loop
antenna at the receiver?
A 25x15mm loop antenna has a theoretical gain Gant_TX = -22dB.
Max allowed path loss is given by:
L  S  Pout  Gant _ TX  Gant _ RX
L  105 10  (27)  (22)  66dBm
Which gives a line-of-sight range:
LOS 

4   10
L
20

0.69
4   10
66
20
 110 m
The 150m line-of-sight range requirement is NOT fulfilled. A receiver
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antenna with HIGHER gain is needed.
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Link budget calculation example
To Range
Calculation 2:
Can the 150m line-of-sight range requirement be achieved with a 35x20mm loop
antenna at the receiver?
A 35x20mm loop antenna has a theoretical gain Gant_TX = -18dB.
Max allowed path loss is given by:
L  S  Pout  Gant _ TX  Gant _ RX
L  105 10  (27)  (18)  70dBm
Which gives a line-of-sight range:
LOS 

4   10
L
20

0.69
4   10
70
20
 174 m
So, a maximum line-of-sight range of 150m can be reached with the
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combination of 18x10mm and 35x20mm loop antennas. This should assure
that the outdoor range R = LOS/2 = 75m requirement can be achieved.电话:021-69522389 地址:中国,上海
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Link budget calculation, ERP specification
To Range
Under Japans weak radio law and the FCC regulations in USA the max level of emitted
power (ERP) from the TX antenna is specified instead of the device output power.
System specification (weak radio system):
Possible outdoor range (R)
: to be decided
Frequency of operation (f0)
: 315.16 MHz (wavelength =0.95m)
Max. emitted power (ERP)
: 500 uV/m @ 3m => ERP ~ -42 dBm
TX & RX antenna gain (Gant_TX, Gant_RX): -22 dB (315 MHz, 35x20mm loop antenna)
Transmitter output power (Pout)
: ERP - Gant_TX = -42 dBm - (-22dB) = -20 dB
Receiver sensitivity (S)
: -105dBm
Line-Of-Sight range
Path loss (L)
TX
Pout
RX
STR-1/
STR-2/STR-3
STR-1/STR-3
Gant_TX
Gant_RX
Sensitivity (S)
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Link budget calculation example, weak radio
To Range
Calculation3:
What outdoor range can be achieved on a link with 315MHz 35x20 loop antennas in
both ends?
A 315 MHz 35x20mm loop antenna has a theoretical gain Gant = -22dB.
Max allowed path loss is now given by:
L  S  ERP  Gant _ RX
L  105 (42)  (22)  41dBm
Which gives a line-of-sight range:
LOS 

4   10
L
20

0.95
4   10
 41
20
 8.5m
The outdoor range are consequently (LOS / 2) = 4.25 m.
NOTE!
Improving Gant_TX will increase range.
In a transceiver solution (nRF403) both
antennas need to be “equal” to meet
regulations and maintain sensitivity both
ways
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To RF System
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SUNBOW STR-1 range example
TX output
power
TX loop
antenna
RX loop
antenna
Theoretical
range
Rule of
thumb:
Outdoor
range
Rule of
thumb:
Indoor
range
+10dBm (10mW)
18x10mm
18x10mm
18x10mm
25x15mm
25x15mm
35x20mm
18x10mm
18x10mm
18x10mm
25x15mm
25x15mm
35x20mm
18x10mm
18x10mm
18x10mm
25x15mm
25x15mm
35x20mm
18x10mm
25x15mm
35x20mm
25x15mm
35x20mm
35x20mm
18x10mm
25x15mm
35x20mm
25x15mm
35x20mm
35x20mm
18x10mm
25x15mm
35x20mm
25x15mm
35x20mm
35x20mm
62m
110m
174m
195m
309m
490m
20m
35m
55m
62m
98m
155m
6.2m
11m
17m
20m
31m
49m
31m
55m
87m
98m
155m
245m
10m
18m
28m
31m
49m
78m
3m
6m
9m
10m
16m
25m
6m
11m
17m
20m
31m
49m
2m
4m
6m
6m
10m
16m
0.6m
1m
2m
2m
3m
5m
0dBm (1mW)
-10dBm (0.1mW)
18x10mm loop antenna: G = -27dB
25x15mm loop antenna: G = -22dB
35x20mm loop antenna: G = -18dB
Rule of thumb:
OUTDOOR RANGE = 1/2 of theoretical LOS link上海桑博科技有限公司
range
INDOOR RANGE = 1/10 of theoretical LOS link range
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Free space (LOS) path loss vs. Frequency
Free space loss (Lp) vs. distance (R) and frequency (fo)
-20
-25
-30
-35
Lp(dB)
-40
fo=315MHz
-45
fo=433MHz
-50
fo=868MHz
-55
fo=2.4GHz
-60
-65
-70
-75
-80
0
10
20
30
40
50
60
70
80
90
100
R(m)
•
Doubling the frequency  6dB added free space loss.
•
6dB added free space loss  cutting the range in half
•
If long range / “good” coverage is the primary key design parameter
 go down in frequency
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Antenna connection methods, antenna impedance
matching, Antennas for nRF designs
To Range
Customers major design goals:
•
Small size
•
Light weight
•
Low cost
•
Lowest possible current consumption
•
Maximum range
The choice of ANTENNA TYPE, CONNECTION METHOD and IMPEDANCE MATCHING
of the antenna to the SUNBOW STR device is of MAJOR importance for the above
issues.
nRFTM
ANT1
ANT2
Differential to
single ended
matching network
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Antenna connection methods
•
The SUNBOW STR devices have a differential (balanced) antenna interface
for easy connection of differential type antennas (e.x loop antenna).
•
XC1
1
20
XC2
VDD
2
19
TXEN
VSS
3
18
PWR_UP
FILT1
4
17
VSS
VCO1
5
16
ANT1
VCO2
6
15
ANT2
VSS
7
14
VSS
VDD
8
13
VDD
DIN
9
12
CS
DOUT
10
11
RF_PWR
A single ended (unbalanced) antenna (e.g. helical antenna) can be
connected to the SUNBOW STR device by the use of a differential to single
ended matching network.
SUNBOW STR devices can be used for both differential and single ended
antennas!
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Antenna differential to single ended matching network
Purpose of the differential to single ended matching network:
•
Differential to single ended conversion
C
C
L
R
nRFTM
A
ANT1
Differential to
single ended
matching network
ANT2
V
L
n
O
x
D
Zload
Differential
•
Zant
A
L
C
C
Single ended
Impedance matching (transformation) between the SUNBOW STR device
recommended antenna port load impedance to the antenna impedance
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Measurement of output power and sensitivity
To Range
Remember the following when measuring transmitter output power and receiver
sensitivity performance:
•
The differential to single ended matching network introduces an insertion
loss of about 2-3dB
•
Losses in connectors and cables typically adds up to about 1-2dB
LF-GENERATOR
SPECTRUM ANALYZER
STR-EVBOARD
Bit rate : 0 - 20 kbps
DIN
DOUT
RF in/out 50 Ohm
Example:
Typical carrier power/modulation bandwidth-testbench
Thus, when measuring performance related parameters, losses in differential to
single ended matching network, connectors and cables must be taken into
account. These losses are typically in the order of 3-5dB.
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Impedance matching to a differential loop antenna
•
To Range
Our loop antennas uses a T-match configuration for matching the high
input impedance of the loop itself, to the recommended load impedance
for the SUNBOW STR device
T-match
The loop antenna is sensitive to changes in layout!
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Antennas suitable for SUNBOW STR devices
The most common / basic antenna types for SRD applications are:
•
Loop antenna
•
Quarter wave dipole antenna
•
Centre-fed half wave dipole antenna
•
Folded, half wave dipole antenna
•
Helical dipole antenna
•
Embedded (integrated) antennas
Line-Of-Sight range
Path loss (L)
TX
Pout
RX
STR-1
STR-2/STR-3
STR-1/STR-3
Gant_TX
Gant_RX
Sensitivity (S)
The customer has to select the appropriate antenna contact the antenna vendor.
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Antennas for SUNBOW STR, Loop antenna
•
Differential (balanced) antenna
-
•
Radiation pattern:
-
•
Narrow, Q  40-50
Impedance:
-
•
-20dB to -30dB
Bandwidth:
-
•
Omi-directional in the plane of the loop
Typical gain in the maximum direction:
-
•
Can be connected “directly” to the differential antenna port of the
nRFTM devices with a T-match
High, several k’s. Transformed down to the required value (e.g.
400) with a T-match
Other characteristics:
-
Suitable for frequency bands 315MHz, 433MHz, 868MHz, 915MHz
-
Inexpensive solution
-
Not dependent on a ground plane
-
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Superior performance in handheld/body-worn applications
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To RF System
Antennas for SUNBOE STR, Quarter wave dipole
•
Single ended (unbalanced) antenna
-
•
To Range
A differential to single ended matching network needed
Radiation pattern:
-
•
Omi-directional in the direction normal to the dipole
axis
Theoretical gain in the maximum direction:
-
•
Bandwidth:
-
•
Wide
Impedance:
-
•
5.1dBi (with infinite ground plane)
About 36 when tuned to resonance
Other characteristics:
-
Suitable for the frequency bands 315MHz, 433MHz, 868MHz, 915MHz,
2.4GHz
-
Dependent on a ground plane
-
Gain decreases considerably when ground plane area spreads out
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less than a quarter wavelength around the base of the
dipole
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Antennas for SUNBOW STR, Centre-fed half wave dipole
•
Single ended (unbalanced) antenna
-
•
Radiation pattern:
-
•
Wide
Impedance:
-
•
2.1dBi
Bandwidth:
-
•
Omi-directional in the direction normal to the
dipole axis
Theoretical gain in the maximum direction:
-
•
A differential to single ended matching
network needed
About 73 when tuned to resonance
Other characteristics:
-
Suitable for the frequency bands 315MHz, 433MHz, 868MHz, 915MHz,
2.4GHz
-
Not dependent on a ground plane
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-
Space consuming
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Antennas for SUNBOW STR, Folded half wave dipole
•
Differential (balanced) antenna
-
•
Wide
Impedance:
-
•
2.1dBi
Bandwidth:
•
Omi-directional in the direction normal to the
dipole axis
Theoretical gain in the maximum direction:
-
•
Can be connected directly to the differential antenna port of the STR
devices
Radiation pattern:
-
•
To Range
About 292 when tuned to resonance
Other characteristics:
-
Suitable for the frequency bands 315MHz, 433MHz, 868MHz, 915MHz,
2.4GHz
-
Not dependent on a ground plane
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-
Space consuming
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Antennas for SUNBOW STR, Helical dipole
•
Single ended (unbalanced) antenna
-
•
Narrow, high Q
Impedance:
-
•
0dBi to -20dBi has been reported
Bandwidth:
-
•
Omi-directional in the direction normal to the helical axis
Typical gain in the maximum direction:
•
A differential to single ended matching network needed
Radiation pattern:
-
•
To Range
About 35  or less, depends on size of coil and orientation
to ground
Other characteristics:
-
Suitable for frequency bands 315MHz, 433MHz, 868MHz, 915MHz
-
Dependent on a ground plane
-
Easily de-tuned (impedance and radiation pattern) by nearby objects
·
-
May not be good for handheld/body-worn use
Extremely high RF currents at feed-point
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Antennas for SUNBOW STR, Embedded antennas
•
Antennas for integration inside enclosures
•
Available from an increasing number of manufacturers
•
Most often single ended (unbalanced) antennas
-
•
Impedance:
-
•
A differential to single ended matching network needed
Most often designed for standard impedance 50 
Other characteristics:
-
Available for all frequency bands 315MHz, 433MHz,
868MHz, 915MHz, 2.4GHz
-
Some antennas available are dependent on a ground
plane, others have a self-contained ground plane
-
Expensive
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Antenna gain vs. Size
Antenna gain increases proportionally with the effective area size of the
antenna. So does range!
18x10 mm: G = -27 dB
25x15 mm: G = -22 dB
35x20 mm: G = -18 dB
This is valid for all types of antennas
Remember: +6dB increase of total antenna gain = twice the range!
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