Reconfigurable RFID Antennas and Applications

This paper discusses the concept of reconfigurable antennas and their applications in various fields, including RFID technology. The article covers the design of a proposed varactor-loaded antenna for RFID tags and the use of fractal antennas in multiband RFID applications.

Reconfigurable RFID antennas and applications
Name of the Student
Name of the University
Abstract- This paper has been focused on the concept of
reconfigurable antennas and its application at various
fields. There have been various development in the field
of communication. A tuning circuit including radio
frequency (RF) switch, passive components have been
integrated with antenna element with DC wires. A
varactor diode that is surface mount has been applied
with a frequency-tuning element at various places of slots
in compact antenna.
Keywords- RFID, Frequency Tuning, Reconfigurable
dipole antenna, Active Antenna
I. INTRODUCTION
Wireless communication has been enhanced by
growing rapidly in the market in recent years. The
collaboration of RFID with various technology has
been including computer technique, integrated circuit
technique and communication technique. There has
been a working range of Radio Frequency
Identification (RFID) technology that covers 13.6
MHz in high band range 100-500 KHz in the low
band range and microwave band range including 860-
960 MHz and 2.45 GHz. RFID technology has been
developing by using Radio Frequency (RF) signals
for automation in identifying objects. In RFID
systems, performance has been the maximum read
range by which RFID reader can be detected.
Therefore, the read range has been sensitive in order
to tag orientation on which tag has been placed. The
antenna helps in determining performance of tag
stuck into a object. The antenna has been determining
performance of tag stuck in the object. The tag
antenna needs to be small in size and low in profile.
The range of frequency from 120-150 KHz is used
for factory data collection and animal detection, the
range of frequency in 13.56 MHz is compatible with
smart cards and ISO compatible memory cards. The
ultra high frequency of 433 MHz is applied in
defense that has active tags in it. The microwave
range is used in WLAN and in Bluetooth standards.
The frequencies in Giga Hertz range requires either
active or semi-active tags. A Radio Frequency
Identification tag has been an antenna compromise
with microchip in a package.
II. RFID SYSTEM OVERVIEW WITH
THEORETICAL CONSIDERATION
A. Antenna equations
The communication in various microwave RFID and
passive UHF systems has been based on
backscattering. RFID tag include an antenna and
microchip that helps in sending information back to
reader and switches between two states. Signals that
RFID reader antenna receives has been forwarded
and reversed by different communication. RFID has
been using simple modulations including amplitude-
shift keying frequency shift keying and phase shift
keying.
Figure 1: Generic backscattered RFID system.
(Source: Nikitin, 2017)
The power density at distance R1 from the
transmitting antenna in the direction (θ trans , φ
trans) is:
Wtrans= {PtransGtrans(θtrans,φtrans)}/4πR2
where Ptrans is the input power of transmitting antenna
and Gtrans is the gain of transmitting reader antenna.
PtransGtrans is called reader-transmitted equivalent
isotropic radiated power (EIRP). The power received
by the RFID tag antenna is expressed by the
following antenna formula:
Ptag=WtransGtag(θtag, φtag) λ2 /4π |ρ trans.ρ tag| 2
The surface waves has been flowing on antenna can
be excited by travelling across dielectric substrate.
However, these waves have reached to edges of
substrate as reflected, diffracted and scattered. This
also help in increasing cross-coupling between array
elements. This excitation of surface waves has been a
function of εr and h. The loss in power of surface
waves has been increased with increase in thickness,
h/ λ0 of the substrate. The loss can be neglected when
h satisfies below criterion:
h /λ0 ≤ 0.3 /2π √εr
B. Varacter-loaded active compact antenna
The equivalent circuit of a rectangular microstrip
antenna has been a parallel combination of resistance

R, inductance L and capacitor C. According to modal
expansion cavity model, the values of R, L and C are
mentioned below:
C = (ε0εelω /2h) cos−2(πd/l)
L = 1 /ω2C
R = Qr /ωC
Qr = C√εr/ 4fh
Here, c is velocity of light, d is the feed-point
location, ω = 2πfr, f r is the design frequency, Qr is
the radiation quality factor, and εe is the effective
permittivity of the medium. The varacter diode when
reverse-biased.
C. Tag antenna structure
This study has been simulated on an FR4 substrate
having relative permittivity of 4.6, width of 1.6 mm
and dimensions of 103*33mm2. This antenna consists
of loop for feeding and meandered dipole. There has
been a proposed RFID diagram, given below:
Figure 2: Schematic of the proposed varactor-
loaded antenna for RFID tag
(Source: Amendola et al. 2018)
The fractal dipole antenna has a rectangular compact
shape and pair of meander patches with a metal
length of 23 mm and a width of 1 mm. There has
been an end gap distance of 2 mm between meander
patch end and microstrip line. The optimal
dimensions of the proposed antenna are W1 = 33
mm, L1 = 41.5 mm, W2 = 3 mm, W3 = 2 mm, L2 =
9.3 mm, L3 = 23 mm, and L4 = 15.2 mm. The
dimensions of the antenna were first studied with
AWR Microwave Office simulation electromagnetic
software and then verified by the experiment.
Figure 3: Radiation pattern comparisons of
proposed antenna: a) radiation patterns of
proposed antenna with all varactors OFF at 2.4
GHz, b) radiation patterns of proposed antenna
with all varactors ON at 2.4 GHz
(Source: Ji et al. 2016)
The authority IEEE meaning of a radio wire as given
by Stutzman Microstrip radio wires are notable for
their highlights, for example, low profile, light
weight, minimal effort, comparability to planar and
non-planar surfaces, inflexible, and simple
establishment. They are most normally fused into
portable, specialized gadgets due to minimal effort
and flexible structures. An accentuation has been
given in microstrip radio wire and reconfigurable
gap, with the end goal to accomplish different octave
tunability. Reconfigurable multiband space radio
wires are accepting a considerable measure of
consideration of late because of the development of
RF-MEMS switches (Chen & Wong 2018).
Regularly microstrip radio wires are additionally
alluded to as fix reception apparatuses (Ji et al. 2016).
The element of self-comparability of a fractal
recieving wire can likewise give a premise to the plan
of various recurrence radio wires. These reception
apparatuses have the preferred standpoint that they
emanate comparable examples in an assortment of
recurrence groups. The significant antecedent is the
broadly examined Sierpinski gasket. The different
fractals shape that gang self-likeness have been
connected to multi-band or scaled down radio wire
structure. There are numerous fractal geometries, for
example, Sierpinski gasket, Sierpinski cover, Koch
Island, Hilbert bend and Minskowsi and so on has
been utilized in fractal radio wires. Reconfigurable
antenna has been demonstrated in various research
papers in the way to switching from single band to
narrow band. The range of frequency from 120-150
KHz is used for factory data collection and animal
detection, the range of frequency in 13.56 MHz is
compatible with smart cards and ISO compatible
memory cards. The ultra high frequency of 433 MHz
is applied in defense that has active tags in it. The

microwave range is used in WLAN and in Bluetooth
standards. These antennas have been helping in
switching the ireless signals into proper wavelength
for clear and concise communication. These
antennas have been helping in enhancing the several
telecommunication fields in the market. The use of
antenna has been creating a revolution in the
telecommunication system. The RFID antennas have
been designed with multiband antenna for RFID
applications for applicable for several standards.
A few strategies were drawn closer in structure the
multifrequency from a solitary radio wire
(Narbudowicz, Ammann & Heberling 2016). To
track the tags attached to objects radio frequency
identification use electromagnetic fields. The
majority of RFID receiving wires were intended to
work at least one recurrence groups, Low Frequency,
Ultra High Frequency, High Frequency and
Microwave. Every one of recurrence groups has their
own favorable circumstances. Accordingly, the desire
of multiband RFID reception apparatuses is getting to
be distinctive. RFID find application in various
sectors including automobile industry. Therefore,
there are numerous papers were structured a
multiband recieving wire for RFID applications
which was pertinent for a few guidelines. Because of
various overall controls, the recurrence groups have
unique areas in the range.
Second dipole arm has been associated with ground.
For this proposed receiving wire, ground plane are
not required. The last measurements of improved
dipole stacked with Cshaped fix structure is appeared
on Table I. The tags can be either active or passive.
Encoded radio signal is transmitted through RFID
reader. The message is received by the tag and then
responds to the identification as well as other
information. A passive tag is cheaper than active as it
does not use any battery. The type of reader and tag
classifies RFID systems. There are two types of tag
like active reader active tag and active reader passive
tag. The improvement is finished by two sections.
For a solitary band, hypothesis of dipole receiving
wire is connected by differing the parameters of L1,
W1, L2 also, W2. For the double band frequencies,
the C-molded fix structure is broke down for
parameters a, b, c and d as clarified partially c. The
space measurement (a mm × b mm) is caused the
recurrence of full and data transfer capacity for upper
band. The examination is done inside the scope of 5
mm ≤ a ≤ 13 mm and 13mm ≤ b ≤ 19 mm. The lower
band is performed relies upon length of dipole and
extent of rectangular fix (c mm × d mm). The scope
of length, c is broke down from 19 mm to 27 mm and
for the length of d, from 18 mm to 22 mm.
III. ANTENNA DESIGN
RFID with passive tags use induced antenna for
voltage operation. The AC voltage that is supplied to
the RFID antenna is rectified by full wave rectifiers
to provide DC voltage. The wavelength of frequency
having value of 13.56 MHz is 22.12 meters. As a
result a true antenna cannot be formed for RFID
antennas. The proposed radio wire is planned on a
Fire Retardant-4 board (FR4) with the measurement
of 90 × 25 mm2 in size which has a relative dielectric
steady of εr = 4.7 with digression loss of 0.019 and it
has a 1.6 mm substrate thickness furthermore, a 0.035
mm copper thickness (Fu & Yang, 2015). A planar
dipole recieving wire is structured as essential
receiving wire reverberating as lower band with
omni-directional radiation design.
The proposed rectangular fix (c × d) as a transmitting
component is intended to be stacked with dipole
radio wire in supporting solid flows and radiation at
reverberation. As appeared in Fig. 1, structure of C-
molded fix is portrayed where an is space width, b is
the opening length, c is the length of the rectangular
fix and d is the length of the rectangular fix. The
consolidated structure of C-formed patches radio
wire what's more, the dipole radio wire at both length
components is observed to be resounding at double
band. The examination of the arrival misfortune
bends when a is shifted is appeared in Fig. 3. The
rectangular fix 19 × 22 mm2 is stacked with dipole
radio wire (when a = 0), just a solitary reverberation
recurrence is performed at 1 GHz. In this manner, as
the estimation of an is shifted in the range, 5 mm ≤ a
≤ 13 mm, the scope of lower recurrence is diminished
from 0.951 GHz to 0.885 GHz and the scope of upper
recurrence is expanded from 2.367 GHz to 2.499
GHz. Besides the investigation of space length is
finished by fluctuated by the scope of 13mm ≤ b ≤ 19
mm as residual the estimation of a = 9 mm, c = 19
mm and d = 22 mm. By changing the measurement of
significant worth b, the bandwith for upper band are
affected and the bandwith of lower band is stay
consistent (Ullah et al., 2018). At point when the
opening length is decreased, the execution of data
transmission and recurrence resounding are changed.
However, data transmission of lower recurrence very
little changes, nearly 80 MHz when the estimation of
b is expanded by 13 mm, 15 mm, 17 mm and 19 mm.
Then again, the thunderous recurrence of upper band
is raised to higher recurrence as the estimation of b is
diminished. The induced voltage in an antenna is
governed by Faraday’s law. . The range of frequency
from 120-150 KHz is used for factory data collection
and animal detection, the range of frequency in 13.56
MHz is compatible with smart cards and ISO

compatible memory cards. The ultra high frequency
of 433 MHz is applied in defense that has active tags
in it. The microwave range is used in WLAN and in
Bluetooth standards. The diameter of reader coil, the
B-field, the number of turns and the DC resistance
can be calculated. The inductance of the various coils
used in the antenna should be calculated. All the
calculation is done following certain formula.
Accordingly, the length space measurement is caused
the recurrence of thunderous and bandwidth for upper
band is changed. As appeared in Fig. 4, the upper
recurrence can be balanced at the point when
estimation of d is differed between the range 18 mm
≤ d ≤ 22 mm by residual the estimation of a = 9 mm,
b = 19 mm and c = 19 mm to play out a required
upper recurrence. In any case, the length of dipole
arms must be stayed as 44.5 mm. As the estimation
of d expanding, the lower recurrence resounding is
somewhat diminished from 0.921 GHz to 0.885 GHz
with the little contrasts of changes that are around
3%. At long last, the investigation of c estimation of
C-formed patches which is caused the resounding
recurrence of lower band affected. The width of
rectangular fix is changed between the range, 19 mm
≤ c ≤ 27 mm. There has been a working range of
Radio Frequency Identification (RFID) technology
that covers 13.6 MHz in high band range 100-500
KHz in the low band range and microwave band
range including 860-960 MHz and 2.45 GHz. RFID
technology has been developing by using Radio
Frequency (RF) signals for automation in identifying
objects. Subsequently, the lower recurrence is
diminished from 0.89 GHz to 0.81 GHz as the
estimation of c is expanded inside the range. The
level of the distinctions of lower recurrence is
relatively 2.3 % when the c is balanced with 19 mm,
21 mm, 23 mm, 25 mm and 27 mm (Rezvani &
Zehforoosh, 2017). In any case the level of contrasts
for upper recurrence is little, 0.3 % where recurrence
run is from 2.466 GHz to 2.493 GHz. In working as a
reconfigurable multiband recieving wire, the switch
is put in the middle of dipole arm and the C-molded
fix recieving wire for the two components
(ElMahgoub, 2016). To work MEMs switch
legitimately, the source what's more, deplete of the
switch ought to keep up voltage 0 V. The coordinate
incorporation of dc predisposition line is intended to
incite the switch and the fix radio wire is associated
with dc ground plane to have the dc coherence. At the
point when the turn is OFF at voltage 0 V, a dipole
reception apparatus is worked as a solitary band. At
the point when the switch is ON, the immediate
current way is made over the hole between the two
patches which is reverberating a lower and upper
recurrence.
IV. CONCLUSION
A minimized dipole reception apparatus was created
and could accomplish a wide data transfer capacity
and viable radiation design over the whole working
band. From the examination of the RFID label
reception apparatuses, it has been discovered that the
feed structure, conservativeness strongly affected the
reception apparatus' working data transmission and
radiation design. There has been a working range of
Radio Frequency Identification (RFID) technology
that covers 13.6 MHz in high band range 100-500
KHz in the low band range and microwave band
range including 860-960 MHz and 2.45 GHz. RFID
technology has been developing by using Radio
Frequency (RF) signals for automation in identifying
objects. Reproduction and estimation results
demonstrated it by picking a fractal shape and a metal
wander fix, tuning their measurements, working
transmission capacity was 12% and stable radiation
examples could be gotten. The label reception
apparatus reaction was estimated as – 65.56 dB at the
2.42 GHz ISM band while the reference recieving
wire reaction was estimated as – 68.07 dB at 2.46
GHz. Moreover, a novel recurrence technique for
minimal dipole reception apparatuses was proposed
and approved through reasonable estimations.
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