Application Note – AN-1370.pdf

AN-1370
APPLICATION NOTE
One Technology Way • P.O. Box 9106 • Norwood, MA 02062-9106, U.S.A. • Tel: 781.329.4700 • Fax: 781.461.3113 • www.analog.com
Design Implementation of the ADF7242 Pmod Evaluation Board Using the Johanson
Technology, Inc., 2450AT18A100 Chip Antenna
by Glaizel Arinuelo
INTRODUCTION
Due to the continuous innovation of technology in radio frequency
(RF) communications, many new designs feature a small form
factor 2.4 GHz band wireless module connectivity. This application
note describes the use and design implementation of the EVALADF7242-PMDZ, a 2.4 GHz wireless transceiver peripheral
module (Pmod™) evaluation board that uses an ADF7242
transceiver in conjunction with a Johanson 2450AT18A100
chip antenna. The chip antenna makes the ADF7242 evaluation
board more compact, more cost effective, and easier to use.
This application note includes printed circuit board (PCB) layout
considerations and simulations used to achieve the optimum
performance of the ADF7242 with a given amount of power.
The ADF7242 has an existing evaluation board, the EVALADF7242DB1Z, which uses a whip antenna in conjunction with
its motherboard, the EVAL-ADF7XXXMB3Z. The design of the
EVAL-ADF7242-PMDZ provides simple and suitable programming
interface connections between the ADF7242 and the host
microcontroller with the use of a Pmod connector. This allows the
customer to use the ADF7242 in various applications. Applications
of a 2.4GHz wireless transceiver include ZigBee, home automation,
consumer electronics, monitoring, and remote control. Transforming the EVAL-ADF7242DB1Z into a low cost, 0.8 in wide,
small profile EVAL-ADF7242-PMDZ makes it more compact and
easier to use without degrading performance.
The ADF7242 is an Analog Devices, Inc., low power transceiver IC
that operates in a 2400 MHz to 2483.5 MHz industrial, scientific,
and medical (ISM) band. It is an extensive, integrated transceiver
solution with excellent performance that is suitable for numerous
wireless network applications. The ADF7242 has two differential
RF ports (RFIO1 and RFIO2) that support antenna diversity and
features programmable data rates, modulation, and an output
power up to 3 dBm. For the complete specifications of the
ADF7242, consult the ADF7242 data sheet.
The EVAL-ADF7242-PMDZ is a flexible and accessible solution
because it supports RF to field-programmable gate array (FPGA)
or processor applications systems that use Pmod-compatible
expansion ports configurable for serial port interface (SPI).
FPGA/
MICROCONTROLLER
SPI
SPI
TRANSCEIVER
TRANSCEIVER
Figure 1. Typical Application Interface System
Rev. 0 | Page 1 of 10
FPGA/
MICROCONTROLLER
13394-001
POWER
SUPPLY
POWER
SUPPLY
AN-1370
Application Note
TABLE OF CONTENTS
Introduction ...................................................................................... 1
General Specifications ......................................................................6
Revision History ............................................................................... 2
Evaluation Board Layout ..............................................................7
Chip Antenna Description .............................................................. 3
PCB Layout Considerations .........................................................8
Evaluation Board Schematic Design .......................................... 6
PCB Layout Simulations ...............................................................8
REVISION HISTORY
11/15—Revision 0: Initial Version
Rev. 0 | Page 2 of 10
Application Note
AN-1370
CHIP ANTENNA DESCRIPTION
Mechanical Dimensions
A chip antenna is a quarter wave monopole antenna that works
with a printed circuit board (PCB) ground plane to form a
dipole system. The 2450AT18A100 Johanson Technology mini
2.45 GHz antenna, a 3.2 mm × 1.6 mm ceramic surface-mount
element, was used in this circuit. Consult the antenna data sheet
when designing the PCB layout. The data sheet contains thorough
layout specifications, including mounting considerations with
or without matching circuits, ground plane clearance, and a
controlled impedance feed line with matching circuits.
Figure 2 shows the mechanical dimensions of the chip antenna.
1.60 ± 0.20
T
0.051 + 0.004/–0.008
1.30 + 0.1/–0.2
a
0.020 ± 0.012
0.50 ± 0.30
a
T
L
Figure 2. Mechanical Dimensions
Mounting Considerations
Figure 3 shows mounting considerations for the chip antenna.
2.6
3.9nH
1.0pF
1.6
4.2
2.7nH
0.4
Value
2400 MHz to 2500 MHz
0.5 dBi typical (XZ-V)1
−0.5 dBi typical (XZ-V)1
9.5 dB minimum
2 W maximum continuous wave
50 Ω
−40°C to +125°C
*LINE WIDTH SHOULD BE DESIGNED TO PROVIDE
50Ω IMPEDANCE MATCHING CHARACTERISTICS.
13394-003
1.9
DIMENSIONS ARE IN mm.
MOUNT DEVICES WITH MARK FACING UP.
Table 1. Johanson 2450AT18A100 Chip Antenna
XZ-V means XZ vertical.
0.063 ± 0.008
*
Table 1 details the specifications of the 2450AT18A100 chip
antenna.
1
3.20 ± 0.20
W
W
Antenna Specifications
Parameter
Frequency Range
Peak Gain
Average Gain
Return Loss
Input Power
Impedance
Operating Temperature Range
MILLIMETERS
0.126 ± 0.008
13394-002
Because it is difficult to have a perfect 50 Ω coplanar waveguide
or feed line between the RF front end and the antenna, include a
pi-matching network or a T-matching network before the chip
antenna. This also allows tuning of the antenna to operate at the
desired operating frequency and to obtain optimum performance.
Achieve maximum power transfer to the chip antenna by
combining a 50 Ω controlled impedance trace and a precise
matching circuit.
INCHES
L
Figure 3. Mounting Considerations
Antenna Performance
The specifications of the 2450AT18A100 chip antenna detailed
in Table 1 and the antenna performance and characteristics
shown in Figure 2 and Figure 3 originate from the antenna data
sheet. The chip antenna is owned by Johanson Technology Inc.,
an independent corporation that is not owned by, controlled by,
or an affiliate of Analog Devices. Analog Devices makes no
representations or warranties with respect to the Johanson
2450AT18A100 or any other Johanson Technology products.
Rev. 0 | Page 3 of 10
AN-1370
Application Note
Figure 4, Figure 5, and Figure 6 originate from the 2450AT18A100
chip antenna data sheet. They show the actual performance of
the chip antenna when used with a Johanson Technoloy evaluation
board. Performance results of the chip antenna differ depending
upon the evaluation board on which the antenna is used.
M1
0
M3
–5
S11
M1
FREQUENCY = 2.370GHz
S11(dB) = –10.643
M2
FREQUENCY = 2.590GHz
S11(dB) = –10.597
–15
M3
M3
FREQUENCY = 2.370GHz
S11(dB) = –15.979
–20
–25
13394-004
–30
1.0
FREQUENCY
(1.000GHz TO 4.000GHz)
1.5
2.0
3.0
2.5
3.5
Figure 6. S11 on a Smith Chart
4.0
FREQUENCY (GHz)
Figure 4. Return Loss with Matching Circuit at 25°C
35
M1
FREQUENCY = 2.4GHz
VSWR AT 25°C = 1.386
30
TA = 25°C
M2
FREQUENCY = 2.5GHz
VSWR AT 25°C = 1.219
M4
FREQUENCY = 2.4GHz
VSWR AT 125°C = 1.606
20
TA = 125°C
M3
FREQUENCY = 2.5GHz
VSWR AT 125°C = 1.332
15
10
5
13394-005
VSWR
25
M4 M3
0
1.0
M1
1.5
2.0
M2
2.5
3.0
3.5
4.0
FREQUENCY (GHz)
Figure 5. VSWR with Matching Circuit at 25°C and 125°C
Rev. 0 | Page 4 of 10
13394-006
S11(dB)
M2
M2
M1
–10
Application Note
AN-1370
XY CUT AT 2.45GHz
VERTICAL
HORIZONTAL
315°
345°
0°
15°
330°
30°
45°
300°
60°
Z
XY-V/XY-H
285°
75°
180°
–40
270°
–30
–20
–10
0
90°
X
90°
270°
105°
255°
120°
240°
XY-CUT
SCANNING DIRECTION
135°
225°
13394-007
Y
0°
150°
210°
195°
165°
180°
Figure 7. 2450AT18A100 Chip Antenna Typical Radiation Pattern, XY Cut at 2.4 GHz (25°C)
345°
XZ CUT AT 2.45GHz
VERTICAL
HORIZONTAL
0°
15°
330°
30°
315°
45°
300°
60°
Z
XY-V/XY-H
285°
75°
180°
–40
270°
–30
–20
–10
0
90°
X
90°
270°
105°
255°
120°
240°
XZ-CUT
SCANNING DIRECTION
135°
225°
13394-008
Y
0°
150°
210°
195°
165°
180°
Figure 8. 2450AT18A100 Chip Antenna Typical Radiation Pattern, XZ Cut at 2.4 GHz (25°C)
345°
YZ CUT AT 2.45GHz
VERTICAL
HORIZONTAL
0°
15°
330°
30°
315°
45°
300°
60°
Z
XY-V/XY-H
285°
75°
180°
–40
270°
–30
–20
–10
0
90°
X
270°
105°
255°
120°
240°
Y
0°
YZ-CUT
SCANNING DIRECTION
135°
225°
150°
210°
195°
180°
Figure 9. 2450AT18A100 Chip Antenna Typical Radiation Pattern, YZ Cut at 2.4 GHz (25°C)
Rev. 0 | Page 5 of 10
165°
13394-009
90°
AN-1370
Application Note
EVALUATION BOARD SCHEMATIC DESIGN
The differential RF port includes a 10 nF coupling capacitor
required as specified in the data sheet. For the transmitter
section, the ADF7242 has an optimum power amplifier (PA)
with a matching impedance of 43.7 + 35.2j Ω at a maximum
output power of 3 dBm. For the receiver section, it has a low
noise amplifier (LNA) with input impedance at the RFIO1 port
of 50.2 – 52.2j Ω and RFIO2 port of 74.3 – 10.7j Ω. An impedance
matched filter balun developed by Johanson Technology matches
those impedances to the antenna source impedance of 50 Ω.
The balun also performs a single-ended to differential conversion
function. Right after the 50 Ω unbalanced port of the filter balun,
implement a pi-matching circuit to properly tune the chip antenna
and obtain optimum antenna performance. For proper layout
guidelines, see the Evaluation Board Layout section of this
application note.
13394-010
The EVAL-ADF7242-PMDZ hardware consists of the ADF7242
2.4 GHz low power transceiver with an SPI communication
interface (Pmod), baluns, matching circuits, and RF chip
antennas. The board is directly powered via the 3.3 V power
supply from the Pmod connector with a very low power
consumption in both receive and transmit modes.
Figure 10. EVAL-ADF7242-PMDZ Hardware
GENERAL SPECIFICATIONS
Table 2 shows the typical performance of the EVAL-ADF7242PMDZ evaluation board achieved at VDD = 3.3 V, TA = 25°C,
fCHANNEL = 2450 MHz, RFIO2 port.
Table 2. Typical Performance of the EVAL-ADF7242-PMDZ
Using the 2450AT18A100 Chip Antenna
Parameter
Output Power
Transmission Range
Current Consumption
Figure 10 shows the EVAL-ADF7242-PMDZ hardware and
Figure 11 shows the simplified connection circuit between the
ADF7242 and the chip antenna.
Value
3 dBm
100 m at 250 kbps
19 mA (Rx mode)
21.5 mA (Tx mode, PO = 3 dBm)
ADF7242
PMOD INTERFACE
RFIO1N
BALANCED PORT
UNBALACED PORT
BALANCED PORT
BALUN
RFIO2P
RFIO2N
BALANCED PORT
UNBALACED PORT
BALANCED PORT
CHIP
ANTENNA
CHIP
ANTENNA
Figure 11. Simplified Connection Circuit Between the ADF7242 and the Chip Antenna
Rev. 0 | Page 6 of 10
13394-011
BALUN
RFIO1P
Application Note
AN-1370
EVALUATION BOARD LAYOUT
Figure 12 shows the PCB layout of the EVAL-ADF7242-PMDZ,
emphasizing the location of two orthogonally mounted chip
antennas (FL1 and FL2). This layout uses the dual differential RF
port interface of the ADF7242, which is configurable for antenna
diversity. The Gerber files of the board layout are available for
download at www.analog.com/EVAL-ADF7242-PMOD.
Pin Number
1
2
3
4
5
6
7
8
9
10
11
12
Signal
CS
SDI
SDO
SCLK
GND
VCC
IRQ1
NC
IRQ2
NC
GND
VCC
Description
Chip select
Serial data in
Serial data out
Serial clock
Power supply ground
Power supply (3.3 V)
Interrupt request output 1
Not connected
Interrupt request output 2
Not connected
Power supply ground
Power supply (3.3 V)
13394-012
The EVAL-ADF7242-PMDZ is a Pmod form factor based on
Pmod interface specifications from Digilent. Table 3 details the
standard pinouts for a 12-pin connector.
Table 3. Pmod Interface Connector (P1) Signal Descriptions
(SPI Communications)
Figure 12. EVAL-ADF7242-PMDZ Board Layout Highlighting the Chip Antenna Placement
Rev. 0 | Page 7 of 10
AN-1370
Application Note
PCB LAYOUT CONSIDERATIONS
PCB LAYOUT SIMULATIONS
For optimum performance between the RF path and the chip
antenna, consider the following when designing the PCB layout:
When designing an RF PCB layout, use simulations to validate
that the PCB layout does not affect the performance of the RF
path. The use of the pi-matching circuit on the actual evaluation
board is necessary to match the PCB trace to 50 Ω, which is the
center of the Smith chart at the desired frequency.






The PCB layout simulation used the Keysight Advanced Design
System (ADS) simulation tool to completely characterize and
optimize the PCB design. The simulation occurs from the RF
differential ports of the ADF7242 up to the chip antenna.
Figure 14 shows the simulation equivalent schematic set up.
Each block in the schematic contains the extracted S-parameter
file for each trace shown in Figure 15 to Figure 17 using the
ADS simulation tool. Also included in the schematic is the
S-parameter file of each RF front-end component used, taken
from manufacturers of the specific components.
Figure 13 shows the FR-4 substrate material of the EVALADF7242-PMDZ PCB evaluation board.
ETCH TOP
FR-4
16.93mil
16.93mil
DRILL THROUGH
DRILL 1 AND DRILL 2
0mil
Figure 13. EVAL-ADF7242-PMDZ Substrate Material
Figure 14. Simulation Equivalent Schematic
Rev. 0 | Page 8 of 10
AIR
13394-014

The EVAL-ADF7242-PMDZ uses a balun filter for
impedance matching and the conversion function from
single-ended to differential. The balun requires vias at its
ground pins.
Ground the stitching around the edges of the board to
eliminate coupling and slot radiation.
Place the regulator capacitors and decoupling capacitors as
close as possible to the transceiver IC.
Design the PCB traces carefully to match the 50 Ω
impedance of the antenna. The impedance of the PCB
traces depends on the dielectric constant of the PCB
material, trace width, and the height above the ground plane.
The chip antenna must be free from the surrounding
ground planes at the distance specified on the
2450AT18A100 chip antenna data sheet.
Ensure that the PCB trace from the balun to the antenna is
as short as possible.
Place the pi-matching circuit at a close proximity and
specific distance to the chip antenna.
Properly mount the chip antenna as specified on the
2450AT18A100 chip antenna data sheet.
13394-013

Application Note
AN-1370
PCB LAYOUT SIMULATION RESULTS
Figure 18 and Figure 19 show the results from simulations
performed on the ADS. The S-parameters describe the
performance of the RF path in terms of the power transfer,
gain, losses, and frequency response.
0
M1
S11 (dB)
–20
M1
FREQUENCY = 2.400GHz
S11 (dB) = –18.139
–40
13394-015
–60
13394-018
–80
Figure 15. Trace from Decoupling Capacitor to Balun Balanced Port
–100
0
1
2
3
4
5
6
7
8
9
10
FREQUENCY (GHz)
Figure 18. Return Loss
Return loss characterizes the amount of power reflected from
the feed line and is a commonly valued parameter for the antenna.
It is usually displayed as S11 in dB. Figure 19 indicates that the RF
radiates at 2.400 GHz, with S11 = −18.139 dB. It is more efficient
than the acceptable return loss of −10 dB to −15 dB and reflects
only 1.58% of the power.
0
M2
13394-016
–0.2
M2
FREQUENCY = 2.400GHz
S21(dB) = –0.084
–0.4
S21(dB)
Figure 16. Trace from Balun Unbalanced Port to Matching Circuit
–0.6
–0.8
–1.2
13394-019
–1.0
0
1
2
3
4
5
6
7
8
9
10
FREQUENCY (GHz)
Figure 19. Insertion Loss
13394-017
Acceptable insertion loss for the PCB layout is less than 1 dB.
Maximize the allowable insertion loss of the PCB to optimize
the RF performance. Figure 19 indicates that an insertion loss of
−0.084 dB has a minimal effect on the power transferred.
Figure 17. Trace from Matching Circuit to Chip Antenna
Rev. 0 | Page 9 of 10
AN-1370
Application Note
Figure 20 shows the corresponding impedance measurements at
the feed line of the antenna. The impedance plot on the Smith
chart helps determine the tuning necessary to improve the
antenna performance at the desired operating frequency.
1.0
2.0
0.5
0.2
M3
FREQUENCY = 2.400GHz
S11(dB) = 0.124/75.511
IMPEDANCE = 51.641 + j12.582
5.0
S11
0.5
0
1.0
2.0
5.0 10.0
20.0
2450AT18A100 Data Sheet. Mini 2.45 GHz Antenna. Johanson
Technology, Inc., 2014.
–20.0
–10.0
–0.2
JTI Chip Antenna Mounting and Tuning Techniques, Johanson
Technology, Inc.
–5.0
–0.5
The design and implementation of the EVAL-ADF7242-PMDZ
using a chip antenna was verified by the use of the ADS simulation
tool. It is important to determine the RF parameters needed in
the simulation, such as return loss, insertion loss, and impedance
of the PCB layout, because these parameters greatly impact the
actual RF performance of the evaluation board. Proper design
of the PCB layout and the RF component results in optimum
performance for both the ADF7242 and the 2450AT18A100
chip antenna.
REFERENCES
10.0
M3
CONCLUSION
–1.0
FREQUENCY
(0GHz TO 10GHz)
13394-020
–2.0
Figure 20. Corresponding Impedance Measurements
©2015 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
AN13394-0-11/15(0)
Rev. 0 | Page 10 of 10
Similar pages