- 0 - 上海桑博科技有限公司电话 :021-69522389 地址 : 中国, 上海 Factors affecting RANGE Prior to starting an RF design a realistic range requirement MUST be established

- 1 -

上海桑博科技有限公司电话 :021-69522389 地址 : 中国 , 上海

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 importance of these factors can be shown in the Line-Of-Sight (LOS) link budget

Can the desired range requirement be achieved or not?

• 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)

To RF System

To Range

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Range- Theoretical LOS link budget

• Allowed transmitter output power (POUT)

The parameters included in LOS link budget calculations are:

TX

POUT

Antenna

matchingnetwork

LM_TX

Gant_TX

RX

Sensitivity (S)

Gant_RX

Line-Of-Sight range (R)

Path loss (LP)

• 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)

To RF System

To Range

Antennamatchingnetwork

LM_RX

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• Range variations caused by multi-path fading

• Objects in close proximity to the antenna thataffects antenna performance, e.g.:

- Printed circuit board (PCB)

- Enclosure, enclosure material

- Human body

• Quality of sampling, detection and processing of received data from the RF device

Range- External losses

Rule of thumb:

OUTDOOR RANGE = 1/2 of theoretical LOS link range

INDOOR RANGE (trough walls) = 1/10 of theoretical LOS link range

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 external losses must be added to the LOS link budget for realistic calculation!

To RF System

To Range

RXTX range 1

P out

Obstacle

Ob

sta

cle

range2b

conducting surface

rang

e 2a

- These losses increases with increasing frequency

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An example on how to achieve long and reliable range

To RF System

To Range

• Coverage to/from base station from/to all nodes

• Big, high gain antennas

• High output power

• Coverage only between neighbouring nodes

• Small, low gain antennas

• Low output power

• Big and bulky radio devices

• High current consumption

• Jamming of other systems

• Compliance with frequency regulations?

• Small, light weight devices

• Low current consumption

• Low interference

• Easy to comply with frequency regulations

This solution implies: This solution implies:

N5 N6 N7

N3 N4

N1 B N2

N5 N6 N7

N3 N4

N1 B N2

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Link budget calculation example

To RF System

To Range

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

TXSTR-1

STR-2/STR-3

Pout

Transmitter antenna gain (Gant_TX): -27dB (18x10mm loop antenna)

G ant_TX

Receiver antenna gain (Gant_RX) : To be decided

G ant_RX

Receiver sensitivity (S) : -105dBm

RXSTR-1/STR-3

Sensitivity (S)

L ine-O f-S ight range

P ath loss (L)

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Calculation 1:Can the 150m line-of-sight range requirement be achieved with a 25x15mm loop antenna at the receiver?

dBmL

GGPSL RXantTXantout

66)22()27(10105

__

Max allowed path loss is given by:

A 25x15mm loop antenna has a theoretical gain Gant_TX = -22dB.

Which gives a line-of-sight range:

mLOSL

110104

69.0

104 20

66

20

The 150m line-of-sight range requirement is NOT fulfilled. A receiver antenna with HIGHER gain is needed.

To RF System

To Range

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Calculation 2:Can the 150m line-of-sight range requirement be achieved with a 35x20mm loop antenna at the receiver?

dBmL

GGPSL RXantTXantout

70)18()27(10105

__

Max allowed path loss is given by:

A 35x20mm loop antenna has a theoretical gain Gant_TX = -18dB.


mLOSL

174104

69.0

104 20

70

20

So, a maximum line-of-sight range of 150m can be reached with the combination of 18x10mm and 35x20mm loop antennas. This should assure that the outdoor range R = LOS/2 = 75m requirement can be achieved.

To RF System

To Range

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Link budget calculation, ERP specification

To RF System

To Range

System specification (weak radio system):

Frequency of operation (f0) : 315.16 MHz (wavelength =0.95m)

Possible outdoor range (R) : to be decided

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)

TXSTR-1/

STR-2/STR-3

Pout

G ant_TX

Receiver sensitivity (S) : -105dBm

G ant_RX

RXSTR-1/STR-3

Sensitivity (S)


P ath loss (L)

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.

Transmitter output power (Pout) : ERP - Gant_TX = -42 dBm - (-22dB) = -20 dB

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Link budget calculation example, weak radio

Calculation3:What outdoor range can be achieved on a link with 315MHz 35x20 loop antennas in both ends?

dBmL

GERPSL RXant

41)22()42(105

_

Max allowed path loss is now given by:

A 315 MHz 35x20mm loop antenna has a theoretical gain Gant = -22dB.


mLOS L 5.8

104

95.0

104 20

41

20

The outdoor range are consequently (LOS / 2) = 4.25 m.

To RF System

To Range

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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SUNBOW STR-1 range example

TX outputpower

TX loopantenna

RX loopantenna

Theoreticalrange

Rule ofthumb:

Outdoorrange

Rule ofthumb:Indoorrange

+10dBm (10mW) 18x10mm 18x10mm 62m 31m 6m18x10mm 25x15mm 110m 55m 11m18x10mm 35x20mm 174m 87m 17m25x15mm 25x15mm 195m 98m 20m25x15mm 35x20mm 309m 155m 31m35x20mm 35x20mm 490m 245m 49m

0dBm (1mW) 18x10mm 18x10mm 20m 10m 2m18x10mm 25x15mm 35m 18m 4m18x10mm 35x20mm 55m 28m 6m25x15mm 25x15mm 62m 31m 6m25x15mm 35x20mm 98m 49m 10m35x20mm 35x20mm 155m 78m 16m

-10dBm (0.1mW) 18x10mm 18x10mm 6.2m 3m 0.6m18x10mm 25x15mm 11m 6m 1m18x10mm 35x20mm 17m 9m 2m25x15mm 25x15mm 20m 10m 2m25x15mm 35x20mm 31m 16m 3m35x20mm 35x20mm 49m 25m 5m

18x10mm loop antenna: G = -27dB25x15mm loop antenna: G = -22dB35x20mm loop antenna: G = -18dB

To RF System

To Range

Rule of thumb:OUTDOOR RANGE = 1/2 of theoretical LOS link rangeINDOOR RANGE = 1/10 of theoretical LOS link range

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Free space (LOS) path loss vs. Frequency

To RF System

To Range

Free space loss (Lp) vs. distance (R) and frequency (fo)

-80

-75

-70

-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

0 10 20 30 40 50 60 70 80 90 100

R(m)

Lp

(dB

) fo=315MHz

fo=433MHz

fo=868MHz

fo=2.4GHz

• 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

• Small size

• Light weight

• Low cost

• Lowest possible current consumption

• Maximum range

Customers major design goals:

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.

To RF System

To Range

AN T 1

AN T 2

Differential tosingle ended

m atching network

nRFTM

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Antenna connection methods

To RF System

To Range

• The SUNBOW STR devices have a differential (balanced) antenna interface for easy connection of differential type antennas (e.x loop antenna).

• 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.

PWR_UPVSS

XC1

ANT1

VDD

DIN

VSS

ANT2

VSS

VSS

FILT1

XC2

TXEN

RF_PWRDOUT

VDD

14

20

19

17

16

15

18

1

2

3

4

5

6

7

8

9

10 11

12

13

VCO1

VCO2

CS

VDD

SUNBOW STR devices can be used for both differential and single ended antennas!

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Antenna differential to single ended matching network

• Differential to single ended conversion

• Impedance matching (transformation) between the SUNBOW STR device recommended antenna port load impedance to the antenna impedance

Purpose of the differential to single ended matching network:

To RF System

To Range

nRF

ANT1

ANT2

RF in/out

L2

C3

Optional

C4L1

L3

VDD

C1

C2

xxx

AN T 1

AN T 2

Differential tosingle ended

m atching network

nRFTM

Differential

ZantZ load

Single endedDifferential

Z load

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Measurement of output power and sensitivity

• The differential to single ended matching network introduces an insertion loss of about 2-3dB

Remember the following when measuring transmitter output power and receiver sensitivity performance:

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.

Example:Typical carrier power/modulation bandwidth-testbench

To RF System

To Range

• Losses in connectors and cables typically adds up to about 1-2dB

DIN DOUT

RF in/out 50 Ohm

STR-EVBOARDSPECTRUM ANALYZERLF-GENERATOR

Bit rate : 0 - 20 kbps

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Impedance matching to a differential loop antenna

• 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

To RF System

To Range

T-match

The loop antenna is sensitive to changes in layout!

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Antennas suitable for SUNBOW STR devices

• Loop antenna

• Quarter wave dipole antenna

• Centre-fed half wave dipole antenna

• Folded, half wave dipole antenna

• Helical dipole antenna

• Embedded (integrated) antennas

The most common / basic antenna types for SRD applications are:

To RF System

The customer has to select the appropriate antenna - contact the antenna vendor.

To Range

RXTX

STR-1STR-2/STR-3

Pout

G ant_TX G ant_RX

STR-1/STR-3

Sensitivity (S)


P ath loss (L)

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Antennas for SUNBOW STR, Loop antenna

• Differential (balanced) antenna

- Can be connected “directly” to the differential antenna port of the nRFTM devices with a T-match

• Radiation pattern:

- Omi-directional in the plane of the loop

• Typical gain in the maximum direction:

- -20dB to -30dB

• Bandwidth:

- Narrow, Q 40-50

• Impedance:

- 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

- Superior performance in handheld/body-worn applications

To RF System

To Range

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Antennas for SUNBOE STR, Quarter wave dipole

• Single ended (unbalanced) antenna

- A differential to single ended matching network needed


- Omi-directional in the direction normal to the dipole axis

• Theoretical gain in the maximum direction:

- 5.1dBi (with infinite ground plane)

• Bandwidth:

- Wide

• Impedance:

- About 36 when tuned to resonance


- 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 less than a quarter wavelength around the base of the dipole

To RF System

To Range

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Antennas for SUNBOW STR, Centre-fed half wave dipole






- 2.1dBi

• Bandwidth:

- Wide

• Impedance:





- Space consuming

To RF System

To Range

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Antennas for SUNBOW STR, Folded half wave dipole

• Differential (balanced) antenna

- Can be connected directly to the differential antenna port of the STR devices




- 2.1dBi

• Bandwidth:

- Wide

• Impedance:





- Space consuming

To RF System

To Range

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Antennas for SUNBOW STR, Helical dipole




- Omi-directional in the direction normal to the helical axis

• Typical gain in the maximum direction:

- 0dBi to -20dBi has been reported

• Bandwidth:

- Narrow, high Q

• Impedance:

- About 35 or less, depends on size of coil and orientation to ground


- 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

To RF System

To Range

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Antennas for SUNBOW STR, Embedded antennas

To RF System

To Range

• Antennas for integration inside enclosures

• Available from an increasing number of manufacturers

• Most often single ended (unbalanced) antennas


• Impedance:

- Most often designed for standard impedance 50


- 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!

To RF System

To Range

Documents

- 0 - 上海桑博科技有限公司 电话 :021-69522389 地址 : 中国, 上海 Factors affecting RANGE Prior to starting an RF design a realistic range requirement MUST be established

- 0 - 上海桑博科技有限公司电话 :021-69522389 地址 : 中国, 上海 Factors affecting RANGE Prior to starting an RF design a realistic range requirement MUST be established