FYP 4th presentation

Design and Simulation of

Passive

UHF RFID Tag

Supervisor: Dr. Irfanullah

Group Members:Haroon Ahmed FA11-BEE-054Nabeel Muqarab FA11-BEE-074Rehan Zaffar FA11-BEE-087

Objectives:

• To design, simulate and fabricate

passive UHF RFID tag.

• To measure input impedance of the

fabricated tag for matching with RFID

tag IC.

Project Phases:

1. Study Phase (2 months)

2. Study and reproducing the results of already designed

RFID Tag research paper. (3 months)

3. a) Optimization of RFID tag studied in phase 2 for

implementation on FR4 substrate. (1 month)

b) Size reduction of (a). (2 months)

4. a) Fabrication and measurement of input impedance

of the RFID tag. (1.5 months)

b) Write up for the conference paper (FIT). (2 weeks)

Block Diagram:

[1] Antenna Theory and Design by Warren L. Stutzman 3rd Edition

Fig.1 Block Diagram of RFID System [1]

Passive RFID Tag System:• Reader

• Emits RF signal.

• Collects Data stored in tag.

• Tag• Converts RF signal to DC voltage

for powering up the circuitry.

• Process and returns RF signal containing identification data.

Introduction:

RFID:A radio frequency identification (RFID) system identifies an object without direct contact through digital wireless techniques.

RFID Allocated Freq. Bands [2]:

Frequency Band Name Frequencies Passive Read Distance

Low Frequency (LF) 120-140 KHz 10-120 cm

High Frequency (HF) 13.56 MHz 10-20 cm

Ultra High Frequency (UHF) 865-928 MHz Less than 10 m

Microwave (MW) 2.45 & 5.8 MHz Less than 3 m

Ultra Wideband 3.1-10.6 GHz 10 m

[2] Antenna Theory and Design by Warren L. Stutzman 3rd Edition

RFID Frequency Bands [3]• USA: 902 – 928 MHz

• China : 840.5 – 844.75 / 920.25 – 924.75 MHz

• Europe : 865- 868 MHz

[3] D. Puente, et al “Matching radio frequency identification tag compact dipole antennas to an arbitrary chip impedance” IET Microwaves, Antennas & Propagation 2008

Reproducing the results of:

S. Sajal, et al “A Low Cost Flexible Passive UHF RFID Tag for Sensing Moisture Based on Antenna Polarization”, IEEE, 2014.

Physical Structure:

.

Fig. 2. Dimension of the Antenna; a= 2 mm, b = 27.35 mm, c = 32.35 mm,d = 38 mm, e = 7.6 mm, f = 3.65 mm, g = 6 mm [4]

[4] S. Sajal et al, “A Low Cost Flexible Passive UHF RFID Tag for Sensing Moisture Based on Antenna Polarization”, IEEE, 2014

Equivalent circuit of RFID Tag IC

(Higgs 2 by Alien Technology):

.

Equivalent Impedance of RFID Tag IC:

15.44 - j151.42 ohm(867 MHz), 13.88 - j143.6 (915 MHz)

Parameters:

• 𝑓 = 915 𝑀𝐻𝑧

• Impedance of Antenna = 13.88 +j143.6

• Impedance of RFID Tag IC = 13.88 - j143.6

• Substrate: FR4 (𝜀𝑟 = 4.6), Paper (𝜀𝑟 = 2.38)

• Gap between two poles = 0.26 mm

• Substrate thickness: FR4 (1.6 mm), Paper (56 microns)

• Copper layer thickness = 32 microns

ADS Model :

Size = 0.136𝜆0 × 0.126𝜆0 (𝜆0= 0.349 m)

Simulation Results:

Scattering parameter:

FR4 SubstratePaper Substrate

Size Reduction and Impedance

Matching(Smith Chart)[5] :

For an antenna to have an admittance of 𝑌𝑎 = 𝑔𝑎 + 𝑗𝑏𝑎 and the chip admittance to be 𝑌𝑐 = 𝑔𝑐 + 𝑗𝑏𝑐 for the optimal power transfer between the antenna and tag 𝑌𝑎 = 𝑌𝑐

∗ at the design frequency

1) Making 𝑔𝑎 = 𝑔𝑐 by scaling

For 𝑔𝑎 = 𝑔𝑐 scaling factor is used

𝞺 =𝑓

𝑓0Where f is either

𝑓 = 𝑓1

Or 𝑓 = 𝑓2

If 𝑓1 < 𝑓2 𝑠𝑜 𝑓1 is chosen for more compact design.




2) Making 𝑏𝑎 = −𝑏𝑐 by short circuit stub.

To make 𝑏𝑎 = −𝑏𝑐 we select the proper value of Reactance.

𝑋𝑠𝑡𝑢𝑏 =1

𝑏𝑐+𝑏

𝑙 =1

𝛽𝑎𝑟𝑐𝑡𝑎𝑛

𝑋𝑠𝑡𝑢𝑏𝑍0

𝑍0 = 𝜂0𝐴

𝑍0 Characteristic impedance (for c = 1.2 mm and b = 1.5 mm ,

𝑍0 =226.5)

𝜂0 Intrinsic Impedance (377 Ohm)




• 𝐴 =2𝜋

ln(2( 1+𝐾𝑎 + 4𝐾𝑎 1 4/ 1+𝐾𝑎 − 4𝐾𝑎

1 4))

• 0 ≤ 𝐴 ≤ 1 , 0 ≤ 𝑘 ≤1

2

• 𝑘𝑎 = 1 − 𝑘2 , 𝑘 =𝑐

𝑐+2𝑏


Proposed Design

Proposed design with reduced

dimensions:

Size = 0.108𝜆0 × 0.063𝜆0 (𝜆0= 0.346 m)

Parameters:

•𝑓 = 867 𝑀𝐻𝑧

• Impedance of Antenna = 15.44 +j151.42

• Impedance of RFID Tag IC = 15.44 - j151.42

•Substrate: FR4

• Gap between two poles = 0.26 mm

• Substrate thickness = 1.6 mm

• Copper layer thickness = 32 microns

Size Comparison:

Size = 21.79 mm x 37.3 mm0.108𝜆0 × 0.063𝜆0(𝜆0= 0.346 m)

Size = 42.78 mm x 47.35 mm0.136𝜆0 × 0.126𝜆0

(𝜆0= 0.349 m)

Simulation results for proposed design:


Simulation results for proposed design :

Impedance plot:


Absolute Field patterns:

E-Plane H-Plane


Directivity and Gain patterns:


Current Distribution:

Read Range Calculation: [6]

Friis Transmission Equation

𝑃𝑟𝑃𝑡

=𝜆

4𝜋𝑅

2

𝐺𝑡𝐺𝑟 (1)

Where R is our read range.

[6] Antenna Theory Analysis and Design by Constantine A. Balanis 3rd Edition

Read Range Example:

Solution:

Equation 1 can be written as:

𝑃𝑟 = 𝐸𝐼𝑅𝑃 + 𝐺𝑟 + 20 log10𝜆

4𝜋𝑅

−13 = 36 + 1 + 20 log10𝜆

4𝜋𝑅

−50 = 20 log10𝜆

4𝜋𝑅

𝑅 = 8.7 𝑚

The RFID tag antenna can respond to -13 dBm of power. If the reader has 36 dBm EIRP

and the tag antenna has 1 dB gain, calculate the passive read distance. Assume free

space propagation conditions and a frequency of 867 MHz.

First

Measurement

Fabricated Antenna:

Antenna is fabricated on FR4 substrate from TIP.

Image Theory [7]:

The monopole antenna results from applying image theory to the dipole. If a conducting plane is placed below a single element of length L/2 carrying a current, then the combined system acts essentially identically to a dipole of length L except that the radiation takes place only in the space above the plane, so the directivity is doubled and the radiation resistance is halved(Figure 3).

Figure 3. Image theory applied to the monopole antenna

[7] ANTENNAS AND PROPAGATION FOR WIRELESS COMMUNICATION SYSTEMS2nd Edition by SIMON R. SAUNDERS

Image Theory :

• The impedance of a monopole antenna mounted vertically above an infinite ground plane is one half of that of a full dipole antenna. For a quarter-wave monopole (L= 𝜆/4 ), the impedance is half of that of a half-wave dipole.

• Theoretically, 7 times the wavelength size of the ground plane behaves almost like an infinite ground plane. For our design, at operating frequency, its dimensions are:

10 ft * 10 ft

Measurement Setup:

Measurement Setup:

Input Impedance Measurement:

• Input impedance is measured using network analyzer.

• Plot of S11 is imported to ADS.

Real Impedance Plot:

Imaginary Impedance Plot:

Comments on First Measurement Results:

• Ground plane (copper) of 10 ft x 10 ft was not available.

• So we used aluminum foil (10 ft x 5 ft) as a ground plane.

• Deviation in measured and simulated results.

Second

Measurements

Designing a Microstrip Balun [8]:

Fig.4 Microstrip Balun

[8] A Broadband unipolar Microstrip to CPS Transition 1997 Asia Pacific Microwave Conference

By changing l1 and l2 so that, l1-l2= 𝜆𝑔/4 it gives the

required results .

Antenna with Balun (ADS Model):

Antenna with Balun (Fabricated):

Top View


Bottom View


Results with Balun:


Questions

and

Answers

FYP 4th presentation

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