Skyetek SKYEMODULE M1 Design Manual

SKYEMODULE M1

ANTENNA DESIGN GUIDE

VERSION 100112

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Skyetek Inc
1525 Market St. Ste 200
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www.skyetek.com

Main 720.328.3425 Fax:[phone]

COPYRIGHT INFORMATION:

Copyright 2012 SkyeTek, Inc., 1525 Market St. Suite 200, Denver, Colorado 80202, U.S.A. All rights reserved.

Version 100112

This product or document is protected by copyright and distributed under licenses restricting its use, copying, distribution, and decompilation. No
part of this product or document may be r eproduced in any form by any means without prior written authorization of SkyeTek and its licens ors, if
any.

TECHNICAL SUPPORT AND CONTACT INFORMATI ON

SkyeTek, Inc.

1525 Market Street. Suite 200

Denver, CO 80202

http://www.skyetek.com

SALES:

[e-mail]

TECHNICAL SUPPORT:

[e-mail]

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TABLE OF CONTENTS

1 About this Document ............................................................................................... 6

1.1 Revision History ............................................................................................... 7

2 Overview .............................................................................................................. 8

2.1 Internal Antenna .............................................................................................. 9

2.2 External Antenna .............................................................................................. 9

3 Custom Antennas ...................................................................................................11

3.1 Design Procedure

............................................................................................11

3.1.1 Example 1

3.1.2 Example 2 – The Internal Antenna of the M1 ......................................................12

3.1.3 Example 3 – Copper Tape External Antenna.......................................................13

...............................................................................................12

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LIST OF FIGURES

Figure 1-1: Example Prototype Antenna .............................................................................. 6

Figure 2-1: Antenna Connector ......................................................................................... 8

Figure 2-2: The SkyeRead EA1 External Antenna .................................................................... 9

Figure 2-3: The SkyeRead EA1 Circuit ................................................................................10

Figure 3-1: Example Antenna Layout .................................................................................13

Figure 3-2: Improved Antenna with Ground Shield .................................................................14

Figure 3-3: Design antenna on metal .................................................................................15

Figure 3-4: Points A and B shown ......................................................................................15

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LIST OF TABLES

Table 1-1: Revision History .............................................................................................. 7

Table 2-1: J2 Pin Descriptions .......................................................................................... 8

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1 About this Document

The SkyeModule M1 is designed for low power RFID applications that require less than 4 inches of read
range when using the internal antenna of the M1. Alternatively, the M1 can directly drive an
external antenna to provide up to 10 inches of read range. For applications that require more than 10
inches of read range, a power amplifier can be used to drive an external antenna.

The SkyeModule M1 comes with an integrated internal antenna. The M1 will also work with standard
external antenna modules, such as the SkyeRead EA1. However, many customers will need to
design custom external antennas to best fit their specific application requirements.

SkyeTek and its partners also provide custom RFID antenna design services.

Figure 1-1: Example Prototype Antenna

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Revision

Author

Change

100112

Brad Alcorn

Releasing new format with minor edits.

1.1 Revision History

Table 1-1: Revision History

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J2

Pin

Name

Description

1

GND

Antenna Ground.

2

ANT

Antenna Output pin. ANT provides 50 ohms output for matching an
external antenna. Jumper ANT to INT to enable the on-board antenna.

3

INT

Internal Antenna pin. Jumper INT to ANT to enable the on-board
antenna. Remove the jumper between INT and ANT to disable the on­board antenna and connect an external antenna.

2 Overvi ew

This antenna design guide provides some basic theory as well as several practical examples of how
to design high performance cost effective RFID antennas for use with the SkyeTek M1 RFID reader
module.

All antenna connections are made at the Antenna Connector J2.

Figure 2-1: Antenna Connector

Table 2-1: J2 Pin Descriptions

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Using an oscilloscope, the typical waveform at ANT of the M1 can be observed. It should look like
a 13.56MHz sine wave, approximately 10Vpp. Note that typically the antenna drive signal at the ANT
pin of J2 is generated when a host first sends a tag command to the M1 in which the RF_F is set (see

SkyeTek Protocol V2 Guide for more details on RF_F).

2.1 Internal Antenna

The internal antenna of the SkyeModule M1 provides 70mm read range and 100mm x 100mm read
coverage. Connect ANT to INT to enable the internal antenna.

2.2 External Antenna

Figure 2-2: The SkyeRead EA1 External Antenna

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Figure 2-3: The SkyeRead EA1 Circuit

In the figure above, inductor L1 is the physical antenna loop.

Zp forms a resonant circuit tuned at

13.56MHz, so there is an amplification of the ANT signal at B. You can measure and compare the
amplitudes of the sine waves at points A and B as you first adjust C3 to get a maximum amplitude
on the signal at B, and then adjust C4 to further maximize the amplitude of the signal at B.

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3 Custom Antennas

Inductive loop RFID antennas can be made from any electrically conducive material such as tape,
wire, or tubing. The basic requirement is that the antenna is a “loop” with one or more turns. As a
general rule, circular and square antenna loops are optimal geometries. The length to width ratio of a
rectangular antenna should not exceed about 3:1. You can design a custom antenna to provide more
read range and more read coverage than you can get from the internal antenna of the M1.

L1 is the RFID loop antenna. The antenna can be made from wire, copper tape, copper tubing, or
other conductive materials.

ANT has a typical output impedance of 50-ohm at 13.56MHz. The external antenna should be
matched to this 50-ohm output drive impedance. The series capacitance Zs provides the matching
adjustment.

3.1 Design Procedure

The following antenna design procedure can be used. Start with a measured or calculated
inductance for L1, then calculate the capacitor values, then measure and adjust for optimal
performance.

1. Determine the inductance of L1.

a. Build and measure the inductance of L1.
b. Design and calculate the inductance of L1.

2. Determine the capacitance Cp. Pick appropriate values for C2 and C3 .

3. Determine the capacitance Cs for matching the M1 output impedance to the antenna input
impedance. Pick appropriate values for C1 and C4.

The resonant frequency of the parallel impedance Zp circuit is governed by the following equation

where,

L1 is the inductance of the antenna loop

R4 is ignored Cp = C2 || C3 ƒ = 13.56MHz is the desired resonant frequency.

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3.1.1 Example 1

Here are the component values of the SkyeRead EA1 external antenna:

C1 = 22pF 0805 ceramic chip capacitor DigiKey p/n PCC220CNCT-ND

C4 = 3 to 10pF variable capacitor DigiKey p/n SG1015-ND

C2 = 100pF 0805 ceramic chip capacitor DigiKey p/n PCC101CGCT-ND

C3 = not present

R4 is not present

L1 = 1.05uH is the loop inductance of the 2-turn PCB antenna trace approximately 95mm x 95mm.

3.1.2 Example 2 – The Internal Antenna of the M1

For the internal antenna of the M1, the component values are as follows:

C1 = 0 ohm resistor

C4 = ___

C2 = 1000pF 0805 NPO ceramic chip capacitor DigiKey p/n PCC101CGCT-ND

C3 = ___

R4 = ___

L1 = 15-nH is the loop inductance of the single-turn PCB antenna trace

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3.1.3 Example 3 – Copper Tape External Antenna

Figure 3-1: Example Antenna Layout

L1 is 1-turn rectangle loop copper tape

X = 170mm

Y = 30mm

W = 10mm

C1 = 47pF dipped mica capacitor

C4 = ___

C2 = 800pF dipped mica capacitor (470||330)

C3 = ___

R4 = ___

While monitoring A and B with an oscilloscope, you will see how this antenna is susceptible to detuning
from mounting on metal and even from the presence of one or more tags. In order to design the
antenna so that you could mount it onto either metal or non-metal and see similar performance, the
antenna can be designed with a ground ring or a shield on a top and bottom layer. The next example
shows a ground ring around the antenna. See the following drawing and picture.

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Figure 3-2: Improved Antenna with Ground Shield

X = 170mm

Y = 30mm

W = 10mm

C1 = 220pF dipped in mica capacitor

C4 = ___

C2 = 1810pF dipped mica capacitor (470||560||560||220)

C3 = ___

R4 is not present

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Figure 3-3: Design antenna on metal

Figure 3-4: Points A and B shown

The following pictures are examples of how to build a prototype antenna. If you will mount the
antenna on metal, then you should design the antenna on metal as shown in Figure 3-3.