Matching Techniques for Miniaturized UHF

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27 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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1

Matching Techniques for Miniaturized UHF
RFID Loop Antennas

Sawaya Lab

M2 Ozawa Kazuhiro

Sawaya
-
Chen Lab.

2

I. INTRODUCTION


UHF(0.9085
-
0.914 GHz) RFID antenna research in Korea


One of the design considerations is antenna
size reduction
.



But, the input impedance of a reduced size antenna is highly
reactive.


Highly reactive becomes troublesome in the antenna design.




In this paper,
two matching techniques

have been proposed.

Sawaya
-
Chen Lab.

3

II. LOOP ANTENNA SIZE REDUCTION
TECHNIQUES


Conventional loop antenna


Total loop length is one
-
wavelength
or even multiple of one
-
wavelength.
→ It resonates.


Total loop length is half
-
wavelength.
→ Its input impedance is quite
reactive.


The small antenna design


Both the input resistance and the
reactance should be appropriately
designed.

The Proposed loop
antenna size (
l
=330mm)

Sawaya
-
Chen Lab.

4

II. LOOP ANTENNA SIZE REDUCTION
TECHNIQUES

Type
-
1


Using dual
-
resonance mode
inside a loop antenna.


With second resonance mode,
the required bandwidth can be
obtained.

Sawaya
-
Chen Lab.

5


Dual
-
resonance mode


The capacitive loading or inductive loading. →
increase electrical length

of an antenna.


Half
-
wavelength dipole antenna inside a loop antenna.



Retuning frequency


A parasitic patch has effect on
lowering its resonance frequency
.

II. LOOP ANTENNA SIZE REDUCTION
TECHNIQUES

Type
-
1

Sawaya
-
Chen Lab.

6


The locus is marked from 0.8 to 1.0 GHz in the simulation.


It goes through the center of the smith chart.

II. LOOP ANTENNA SIZE REDUCTION
TECHNIQUES

Type
-
1

Substrate thickness

0.787 mm

Dielectric constant
e
re

2.2

Impedance locus in the smith chart.

Simulation

Sawaya
-
Chen Lab.

7

Type
-
2

II. LOOP ANTENNA SIZE REDUCTION
TECHNIQUES


Using folded dipole loop antenna.

Sawaya
-
Chen Lab.

8

II. LOOP ANTENNA SIZE REDUCTION
TECHNIQUES


The half
-
wavelength folded dipole antenna.


The input resistance can be increased by the parasitic
element.




Z
D

is the input impedance of the single dipole


The term
a

depends on the widths of the driven element
and parasitic element or the spacing between these two
elements.


Fine frequency tuning.


A capacitive loading is added inside the folded dipole loop
antenna.

Type
-
2

D
IN
Z
Z
2
)
1
(
a


Sawaya
-
Chen Lab.

9


The smith chart locus follows 50 ohm line.


It resonates at 0.912 GHz.

Substrate thickness

0.787 mm

Dielectric constant
e
re

2.2

Type
-
2

II. LOOP ANTENNA SIZE REDUCTION
TECHNIQUES

Impedance locus in the smith chart.

Simulation

Sawaya
-
Chen Lab.

10

III. RESULTS


Fabricated antennas

Sawaya
-
Chen Lab.

11

III. RESULTS


The simulated radiation efficiencies
are 0.42(Type
-
1) and 0.93(Type
-
2).


Type
-
1 antenna : the loading
effects can cause low radiation
efficiency.

Sawaya
-
Chen Lab.

12

IV. CONCLUSION


Two matching techniques are proposed.


Type
-
1

: Dual resonance modes are created inside loop antenna.


First resonance mode : inductive and capacitive loading.


Second resonance mode : a dipole antenna inside the loop.


Type
-
2

: The folded dipole loop is formed with the capacitive
loading.


Folded dipole : increase the input resistance.


Capacitive loading : lower the resonance frequency.




Both the proposed techniques are suitable for matching small
loop antenna.


They realized
80% size reduction
.