Volume 3, Issue 2, August 2013 Plasma Effect on … 3/Issue 2/IJEIT1412201308_22.pdfVolume 3, Issue...
Transcript of Volume 3, Issue 2, August 2013 Plasma Effect on … 3/Issue 2/IJEIT1412201308_22.pdfVolume 3, Issue...
ISSN: 2277-3754
ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT)
Volume 3, Issue 2, August 2013
119
Abstract—A single rectangular microstrip patch antenna
operating in S band at resonance frequency near 2.15 GHz has
been studied in the existence of cold plasma as a layer covering the
patch antenna. Microwave Office Package is used to design the
rectangular microstrip antenna and to analyze some plasma
parameters at different conditions. Cavity model is also used in the
microstrip antenna to study the plasma when it is considered as a
medium between the patch and ground. Expressions of cold
plasma and their coefficients in the conditions of plasma
interaction operating microwave frequencies are investigated and
presented in details. The radiation pattern, input impedance and
resonance frequency for dominant TM01 mode are calculated for
different plasma conditions. The results presented in this research
may be useful when designing antennas in case of existing plasma
conditions in space system.
Index Terms— Cavity model, Cold Plasma, Rectangular
Microstrip Antenna, TT&C.
I. INTRODUCTION
Antennas have been an essential reciprocal device
employed in telemetry and telecomands (TT&C) space
systems. Microstrip patches are one of suitable elements for
array antennas because of their low weight, better
aerodynamic properties, easy covered by protection layer and
low fabrication cost for aerospace vehicle, like satellites and
reusable space shuttles [1], [2]. However, during re-entry
into earth's atmosphere, a plasma sheath is formed around the
vehicles. A major problem confronting the aerospace
engineers in the space mission is the estimation of the effect
of plasma on the radiation properties of an antenna mounted
on aerospace vehicles or satellites. The plasma sheath may be
seriously affects system performance. Sometimes these
conditions caused interruption of communication link
because of changing the input impedance of the antenna and
may be highly mismatch occurrence. Due to the interaction of
electromagnetic field with plasma in certain parameters value
for plasma frequency, collision frequency and plasma
thickness may be add another effect on such interruptions.
In this work a detailed theoretical formulation on the
isotropic cold plasma, which is normally occurred in space
applications and its interaction with electromagnetic radio
frequencies is presented. A rectangular microstrip antenna
operating in dominant mode TM01, is taken as an important
element in studying the plasma effects. Cavity model
analysis is taken in this report for studying some plasma
conditions on the patch antenna input impedance.
The existence of plasma near conformal microstrip
antennas in flight vehicles operates and below plasma
frequency gives special performance conditions. In
hypersonic missile flight, high temperature generation is
produced. So that, a slap of ceramic material covers the
conductive patch antenna for protection purposes. The
ceramic materials properties at X band are illustrated in Table
I. The plasma effects on receiver antenna are also taken into
account. Different computed and published results are
demonstrated and discussed to illustrate some important
parameters contribution in the antenna.
Table I: Representative values for ceramic materials at X band
Material Relative
permittivity 𝜺′ Loss tangent
𝐭𝐚𝐧 𝜹
Alumina 9.4 - 9.6 0.0001 -0.0002
Boron nitride 4.2 – 4.6 0.0001-0.0003
Beryllia 4.2 0.0005
Borosilicate glass 4.5 0.0008
Pyroceram 5.54 -5.65 0.0002
Rayceram 4.7 -4.85 0.0002
Slip cast fused silica
(SCFS) 3.30 – 3.42 0.0004
Woven (3D) quarts 3.05 – 3.1 0.001-0.005
Silicon nitride
(HPSN) 7.8 – 8.0 0.002-0.004
Silicon nitride
(RSSN) 5.6 0.0005-0.001
Nitroxyceram 5.2 0.002
Reinforced celasin 6.74 0.0009
Plasma Effect on TM01 Mode Rectangular
Microstrip Antenna for Space Telemetry and
Telecomands Subsystems Applications Abdulkareem A. A. Mohammed
1 and Dhirgham K. Naji
2
1Head of
Atmosphere and Space Science Center, Directorate of Space & Communication, Ministry of Science
and Technology, Baghdad, Iraq
2Department of Electronic and Communications Engineering, College of Engineering, Alnahrain University,
Baghdad, Iraq
E-mail: [email protected], [email protected]
ISSN: 2277-3754
ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT)
Volume 3, Issue 2, August 2013
120
II. THEORETICAL FORMATION
A. Electromagnetic Interaction with Plasma
The approach presented here follows closely the material
developed in some published texts [3-5]. By using the cold
plasma approximation, the equation of motion of an electron
mass m and charge 𝑞 in electric field of amplitude 𝐸 and
angular frequency 𝜔, with collision frequency vc acting as
damping force and when the electron velocity equal to v:
−𝑞𝐸𝑒𝑗𝜔𝑡 = 𝑚𝑑𝑣
𝑑𝑡+ 𝑚𝑣𝑐𝑣 (1)
The current density 𝐽 per unit volume is given by
𝐽 = −𝑁𝑞𝑣 (2)
The complex conductivity of the medium is equal to the ratio
of the current density to field
𝜎𝑐 =𝐽
Eejωt=
𝑁𝑞2
𝑚(vc + 𝑗𝜔) (3)
𝜎𝑐 = 𝜎 ′ − 𝑗𝜎′′ =𝑁𝑞2
𝑚휀0∙
휀0vc
𝑣𝑐2 + 𝜔2
− 𝑗𝑁𝑞2
𝑚휀0∙
휀0𝜔
𝑣𝑐2 + 𝜔2
(4)
The quantity (𝑁𝑞2 𝑚휀0) is the natural angular frequency
specific to the electrons which is given by 𝜔𝑝 = 2𝜋𝑓𝑝 . Where
𝑓𝑝 is called plasma frequency and practically defined by
𝑓𝑝 = 8970𝑁−1 2 (5)
where 𝑓𝑝 in [Hz] and N is the number of electrons per cm-3.
The collision frequency vc is given by
vc = 𝑛𝑛𝜎 𝑘𝐵𝑇𝑚 (6)
where 𝑛𝑛 is the number density of neutral species, 𝜎 is the
collision cross section, 𝑘𝐵 is the Boltzmann’s constant, and
m is the electron mass.
Referring to Maxwell equations the complex dielectric
constant related to conductivity by the expression
εc = 휀′ + 𝑗휀 ′′ = 휀0 +𝜎𝑐
𝑗𝜔 (7)
For convenience, two dimensionless quantities, the
normalized electron density 𝑋 and the normalized collision
frequency 𝑍 are introduced:
𝑋 = 𝜔𝑝
𝜔
2
(8𝑎)
𝑍 = 𝑣𝑐
𝜔
2
(8𝑏)
So
𝜎 ′ = 휀0𝜔𝑋𝑍
1 + 𝑍2 (9𝑎)
𝜎′′ = 휀0𝜔𝑋
1 + 𝑍2 (9𝑏)
And
Fig. 1. Real dielectric constant of plasma at different collision
frequency 𝒗𝒄.
휀′ = 휀0 1 +𝑋
1 + 𝑍2 (10𝑎)
휀′′ = 휀0𝑋
1 + 𝑍2 (10𝑏)
In the absence of any collisions 𝑍 = 0 and the relative
dielectric constant is real and equal to (1 − 𝑋). It varies with
frequency (i.e. it is dispersive medium) from (휀 = −∞) for
the lowest frequency to (휀 = 1) for high frequencies, passing
through (휀 =0) for 𝑋 = 1, Fig. 1.
In the case of plane wave, the propagation constant 𝛾 ,
wave number 𝐾 and the dielectric constant are related by the
following relationship:
𝛾 = 𝛼 + 𝑗𝛽 = 𝑗2𝜋
𝜆 εc
휀0
1 2
= 𝑗 𝐾𝜔
𝑐=
𝐾
𝑗 (11)
While the skin depth, the depth which the incident wave is
attenuated by factor (1/𝑒), of plasma media computed by:
𝑃𝑝 =1
𝛼 (12)
It is important to determine the conditions under which the
plasma can be considered as a conductor, and those under
which it can be considered a dielectric. From the ratio of
conduction current to displacement current 𝜎′ 𝜔휀′ the
nature of material can be determined. The point at which
these two currents are equal is generally considered as the
boundary between conductive media 𝜎′ 𝜔휀′ ≫ 1 and
dielectric media 𝜎′ 𝜔휀′ ≪ 1 . In the case of plasma, this
condition can be calculated as:
𝜎 ′
𝜔 휀′ =
𝑋𝑍
1 − 𝑋 + 𝑍2 (13)
ISSN: 2277-3754
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Volume 3, Issue 2, August 2013
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Fig. 2. Boundary between conducting plasma and dielectric
plasma.
Fig. 2 shows the curve representing the boundary between
conductive plasma and dielectric plasma. The behaviour of
plasma as a function of frequency, from the point of view of
refractive index, can now be described briefly. The complex
refractive index defined
𝑛 = 𝑛1 − 𝑗𝑘1 = −𝑗𝛾𝑐
𝜔= 𝐾 (14)
where 𝑛1 and 𝑘1 are the real refractive index and attenuation
index, respectively, and they defined as[3]
𝑛1 = 1
2𝑟 +
1
2 𝑟2 + 1 − 𝑟 2 ∙
𝑣𝑐
𝜔
2
1 2
1 2
(15𝑎)
𝑘1 = −1
2𝑟 +
1
2 𝑟2 + 1 − 𝑟 2 ∙
𝑣𝑐
𝜔
2
1 2
1 2
(15𝑏)
where
𝑟 = 1 −𝜔𝑝
2
𝜔2 + 𝑣𝑐2 (16)
and the dielectric constant of the plasma
εc = ε0 ∙ 𝑛2 (17)
and the intrinsic impedance of non magnetized plasma
medium is
ηc = 𝜇0
εc
(18)
In case of low loss plasma (𝑣𝑐 << 𝜔𝑝 ), three frequency
regions may be defined as follow:
Low Frequencies Case 𝜔 < 𝑣𝑐 , we observe that 𝑛1,
𝑘1 are nearly equal. Expanding in the limit (𝜔 << 𝑣𝑐 , 𝑣𝑐
2 << 𝜔𝑝2 ) , one can obtained the following
indexes equations:
𝑛1 ≈ 𝜔𝑝
2
2𝜔𝑣𝑐
1 2
1 −𝜔
2𝑣𝑐 (19𝑎)
𝑘1 ≈ 𝜔𝑝
2
2𝜔𝑣𝑐
1 2
1 +𝜔
2𝑣𝑐 (19𝑏)
Intermediate Frequencies Case (𝑣𝑐 < 𝜔 < 𝜔𝑝) . In
this region the propagate an electromagnetic wave is
forbidden due to plasma, where the waveguide below
cutoff. Expanding in the limit (𝑣𝑐2 << 𝜔2 << 𝜔𝑝
2 )
we obtained the following indexes equations:
𝑛1 ≈𝑣𝑐𝜔𝑝
2𝜔2 1 −
5𝑣𝑐2
8𝜔2+
𝜔2
2𝜔𝑝2 (20𝑎)
𝑘1 ≈𝜔𝑝
𝜔 1 −
3𝑣𝑐2
8𝜔2−
𝜔2
2𝜔𝑝2 (20𝑏)
High Frequencies Case (𝜔 >> 𝜔𝑝 ). Here, the plasma
becomes a relatively low loss dielectric. in the limit
(𝑣𝑐2 << {𝜔2 -𝜔𝑝
2} and υc2 << 𝜔2{𝜔2 -𝜔𝑝
2 }2 /𝜔𝑝
4 )
the following indexes equations are obtained:
𝑛1 ≈ 1 −𝜔2
𝜔𝑝2
1 2
(21𝑎)
𝑘1 ≈𝑣𝑐𝜔𝑝
2
2𝜔3 1 −
𝜔2
𝜔𝑝2 (21𝑏)
Note that the refractive index is quite insensitive to
collisional damping and the attenuation for the assumed
conditions.
B. Theoretical Formulation of Microstrip Antenna
A microstrip patch antenna consists of a very thin metallic
patch placed a small fraction of wavelength above a
conducting ground-plane. The patch and the ground-plane
are separated by a dielectric layer. The dielectric substrate is
usually non-magnetic and low loss material, (see Fig. 3).
Due to the simple geometry of the microstrip patch
antenna, the half-wave rectangular patch is the most
commonly used microstrip antenna. It is characterized by its
length 𝐿 , width 𝑊 and thickness ℎ . The patch is fed by
coaxial feed to excite the cavity field. The inner conductor of
the coaxial line is connected to the radiating patch while the
outer is connected to the ground-plane as shown in Figure 3.
A cavity model for the microstrip antennas is based on
considering close proximity between the microstrip antenna
and ground plane. So that E field has only the z component
and the H has only the xy-components in the region bounded
by the microstrip and the ground plane. The field in the
aforementioned region is independent of the z-coordinate for
all frequencies of interest. The electric current in the
microstrip must have no component normal to the edge at any
point on the edge, which implies that the tangential
component of H along the edge is negligible. Thus the region
between the microstrip and the ground plane may be treated
as a cavity bounded by a magnetic wall along the edge, and
by electric walls from above and below [6, 7].
10-2
10-1
100
101
102
10-1
100
101
102
Boundary between conducting plasma & dielectric plasma
(W/Wp)2
Vc/W Conductor plasma
Dielectric plasma
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Volume 3, Issue 2, August 2013
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Fig. 3. The rectangular microstrip geometry.
The resonance frequency of m, n order mode 𝑓𝑚𝑛 depends
on the patch size, cavity dimension, and the filling dielectric
constant [8, 9]
𝑓𝑚𝑛 ≈𝑘𝑚𝑛
2𝜋 휀𝑟 (22)
where 𝑚, 𝑛 = 0, 1, 2…
𝑘𝑚𝑛 = Wave number at m, n mode
𝑐 = Velocity of light
휀𝑟 = Relative dielectric constant
And
𝑘𝑚𝑛 ≈ 𝑚𝜋 𝑊 2 + 𝑚𝜋 𝐿 2 (23)
where
𝑊 = Width of the microstrip antenna
𝐿 = Length of the microstrip antenna
The radiating edge W, patch width, is usually chosen such
that it lies in the range (𝐿 < 𝑊 > 2𝐿), for efficient radiation.
The ratio 𝑊/𝐿 = 1.5 may give good performance according
to the side lobe appearances.
In practice the fringing effect causes the effective distance
between the radiating edges of the patch to be slightly greater
than 𝐿. Therefore, the actual value of the resonant frequency
is slightly less than 𝑓𝑟 . Taking into account the effect of
fringing field, the effective dielectric constant for TM01 mode
is derived using [9,11]
𝐿 =𝑐
2𝑓𝑟 휀𝑟
− 2∆𝑙 (24)
Hence
𝑓𝑟 𝑒𝑓𝑓 =𝑐
2 𝐿 + 2∆𝑙 휀𝑟
(25)
with
휀𝑒𝑓𝑓 =휀𝑟 + 1
2+
휀𝑟 − 1
2
1
1 + 10ℎ/𝑊 (26)
and
∆𝑙 = 0.412ℎ 휀𝑒𝑓𝑓 + 0.3 𝑊/ℎ + 0.264
휀𝑒𝑓𝑓 − 0.258 𝑊/ℎ + 0.813 (27)
where
∆𝑙 = Line extension
휀𝑒𝑓𝑓 = Effective dielectric constant
ℎ = Dielectric substrate thickness
The electric field is assumed to act entirely in the
z-direction and to be a function only of the x and y
coordinates
𝐸 = 𝑧𝐸𝑧 𝑥, 𝑦 (28)
The z-component of the electric field 𝐸𝑧 satisfies the two
dimensional form of partial differential equation, the
so-called wave equation
𝜕2𝐸𝑧
𝜕𝑥+
𝜕2𝐸𝑧
𝜕𝑦+ 𝑘2𝐸𝑧 = 0 (29)
Equation (29) cannot be solved without specifying some
boundary conditions for the patch. An obvious requirement is
that the outward current flowing on the perimeter of the patch
must be zero. It may be shown that this requirement is
approximately equivalent to
𝜕𝐸𝑧
𝜕𝑛= 0 (30)
Solving equation (29) subject to the requirement (30) and
using separation of variable, the electric field of the m and n
mode number associated with 𝑥 and 𝑦 direction in a
rectangular resonator with dimensions 𝑊 and 𝐿 can be
written in the form [9].
𝐸𝑧 = 𝐸0 cos 𝑚𝜋𝑥/𝑊 𝑛𝜋𝑦/𝐿 (31)
Now to calculate the far field, aperture model is used. The
resonator surface considered to be as a set of four slots of
width 2𝑎 [12]. By using Green's function and after many
mathematical steps, the general form of the far field for any
(𝑚, 𝑛) mode is in the following form:
𝐸 𝑟 =𝑗𝑘𝑒−𝑗𝑘𝑟
2𝜋𝑟𝐸0 𝑖𝜃 𝐸𝑥 𝜉, 𝜂 cos 𝜑 + 𝐸𝑦 𝜉, 𝜂 sin 𝜑
+ 𝑖𝜑 −𝐸𝑥 𝜉, 𝜂 sin 𝜑 cos 𝜃 + 𝐸𝑦 𝜉, 𝜂 cos 𝜑 cos 𝜃 (32)
where
𝐸𝑥 = ℎ𝐸0 −1 − −1 𝑚 ∙ 𝑗 sin 𝜉𝑊
2 + 1 − −1 𝑚 ∙
∙ cos 𝜉𝑊
2 ∙
𝐿
2𝑠𝑖𝑛𝑐 𝜉𝑎 ∙ 𝑗𝑛 ∙ 𝑠𝑖𝑛𝑐(
𝜉𝐿
2+
𝑛𝜋
2) +
−1 𝑛𝑠𝑖𝑛𝑐(𝜉𝐿
2−
𝑛𝜋
2) (33𝑎)
W
L
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𝐸𝑦 = ℎ𝐸0 −1 − −1 𝑛 ∙ 𝑗 sin 𝜉𝐿
2 + 1 − −1 𝑛 ∙
∙ cos 𝜉𝐿
2 ∙
𝑊
2𝑠𝑖𝑛𝑐 𝜉𝑎 ∙ 𝑗𝑚 ∙ 𝑠𝑖𝑛𝑐(
𝜉𝑊
2+
𝑛𝜋
2) +
−1 𝑚𝑠𝑖𝑛𝑐(𝜉𝑊
2−
𝑛𝜋
2) (33𝑏)
Then the far field components are
𝐸𝜃 =𝑗𝑘𝑒−𝑗𝑘𝑟
2𝜋𝑟 𝐸𝑥 cos 𝜑 + 𝐸𝑦 sin 𝜑 (34𝑎)
𝐸𝜑 =𝑗𝑘𝑒−𝑗𝑘𝑟
2𝜋𝑟 −𝐸𝑥 sin 𝜑 cos 𝜃 + 𝐸𝑦 cos 𝜑 cos 𝜃 (34𝑏)
with
𝜉 = 𝑘 𝑠𝑖𝑛 𝑐𝑜𝑠
= 𝑘 𝑠𝑖𝑛 𝑠𝑖𝑛
𝑘 = 2𝜋/𝜆𝑜
0 =wavelength of free space
Normalizing the input voltage at the feed point (𝑥0 , 𝑦0) to
1V, one can write
ℎ𝐸𝑧 𝑥0 , 𝑦0 = 1 (35)
Using the expression of the closed-cavity resonator model,
the maximum amplitude of the field 𝐸𝑧 is
𝐸0 = ℎ ∙ cos 𝑚𝜋𝑥0
𝑊 ∙ cos
𝑛𝜋𝑦0
𝐿
−1
(36)
where
𝐸0 = Maximum amplitude of the 𝐸𝑧 field
The input impedance of the microstrip antenna fed by a
coaxial probe is 𝑍𝑖𝑛 = 𝑅𝑖𝑛 + 𝑗𝑋𝑖𝑛 . At resonance the
impedance is purely resistive (𝑋𝑖𝑛 = 0). Then the impedance
may be represented by a parallel RLC circuit
𝑍𝑖𝑛 =𝑘
1𝑅
+ 𝑗𝜔𝑐 +1
𝑗𝜔𝐿
(37)
Where at 𝑘 = 1.5, the results give excellent agreement with
the measured and microwave office package results. The
resistance of the patch can be written as
𝑅 =𝑉2
2𝑃𝑇
(38)
where 𝑃𝑇 = 𝑃𝑟 + 𝑃𝑐 + 𝑃𝑑 (39)
𝑉 = Terminal voltage
𝑃𝑇 = Total power dissipated by the antenna
The radiated power outside the antenna surface is
𝑃𝑟 =1
2𝑍0
𝐸𝜗 2 + 𝐸𝜑 2𝑟2 sin 𝜗𝑑𝜗𝑑𝜑
𝜋 2
𝜗=0
2𝜋
𝜑=0
(40)
where
𝑍0 = Characteristic impedance of free space.
The power losses inside the dielectric is
𝑃𝑑 =𝜔0휀0휀𝑟 tan 𝛿
2 𝐸. 𝐸∗𝑑𝑣
𝑣
(41)
where
= Angular operating frequency
𝑡𝑎𝑛 =Loss tangent of the dielectric layer of the patch
The power losses inside the conductor surface of radiator and
the ground plane is
𝑃𝑐 = 2𝑅𝑠
2 𝐻𝑥
2 + 𝐻𝑥𝑦2 𝑑𝑥𝑑𝑦 (42)
where
𝑅𝑠 = 𝜔𝜇0𝜇𝑟
2𝜎 (43)
𝑅𝑠 = Surface resistance
𝐻𝑥 =𝑗
𝜔𝜇 𝜕𝐸𝑧
𝜕𝑦 (44𝑎)
𝐻𝑦 =−𝑗
𝜔𝜇 𝜕𝐸𝑧
𝜕𝑥 (44𝑏)
The inductance and the capacitance of the patch are
respectively
𝐿 =𝑅
2𝜋𝑓𝑟𝑄𝑇
(45𝑎)
and
𝐶 =𝑄𝑇
2𝜋𝑅𝑓𝑟 (45𝑏)
The total quality factor 𝑄𝑇 is
𝑄𝑇 = 𝑅 𝐿
𝐶 (46𝑎)
In other meaning
𝑄𝑇 =𝜔𝑊𝑇
𝑃𝑇
(46𝑏)
𝑊𝑇 =휀0휀𝑟
2 𝐸𝑧
2𝑑𝑣
𝑣
(47)
C. Antenna Coating Material as Plasma Protector
The existence of plasma around and above conformal
antennas may appears in flight vehicles operating at and
below about 4 Mach and missiles. A high temperature
generation in hypersonic missile may use slab of Ceramic
material on conductive patch antenna. Table 1 lists
representative values for ceramic materials [13]. Most of
these materials have suitable electrical properties for high
velocity applications. For instance, Aluminium oxide, Pyroceram and Rayceram have been widely used for space
vehicles. They are hard and have fair rain erosion resistance
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Volume 3, Issue 2, August 2013
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but are difficult to grind to shape. Pyroceram has a higher
dielectric constant than either Rayceram or alumina, which
implies tighter mechanical tolerances in manufacture.
D. Antenna Impedance of Plasma
Immersing an antenna in an ionized medium with a
refractive index different from that of the vacuum has the
effect of modifying the impedance presented by this antenna.
The input impedance of an antenna 𝑍𝑎 in a medium of index
(𝑛) to be related to the impedance of the antenna in vacuum,
at an angular frequency (𝑛𝜔).
1
𝜂𝑍0(𝜔, 휀, 𝜇) =
1
𝜂0
𝑍𝑎(𝑛𝜔, 휀, 𝜇0) (48)
In case of gaseous plasma, 𝜇 = 𝜇0 and 휀 = 𝑛2휀0 the
expression become [3].
𝑍𝑎(𝜔, 𝑛2휀0) =1
𝑛 𝑍𝑎(𝑛𝜔, 휀0) (49)
Input impedance at real refractive index plasma: In the
case where the refractive index is real (𝑋 < 1 𝑎𝑛𝑑 𝑍 ≈0),
the angular frequency 𝑛 ω is a multiple of angular
frequency ω and the impedance at this angular frequency
is accessible both to measurement and calculation.
Input impedance at complex refractive index plasma: In
the case of complex n, the frequency 𝑛𝑓 is also complex
[5]. It is, however, well defined mathematically, and if
there is an analytical formula for impedance in vacuum,
the impedance of the antenna in plasma can be deduced
from it.
E. Effect of Plasma Layer on Receiving Antenna
Noise generated by the receiver is characterized by its
noise figure, 𝑁. The ratio of the maximum available noise
power at the output of the receiver 𝑁𝑜𝑢𝑡 to the maximum
noise power that there would be if there were no noise source
other than the generator connected to the receiver input at
standard reference temperature 𝑇0 = 290 °𝐾 (i.e. 𝐺𝑘𝐵𝑇0𝐵0)
is called as noise factor [ 14 ].
𝑁𝐹 =𝑁𝑜𝑢𝑡
𝐺𝑘𝐵𝑇0𝐵0
(50)
where
𝐺 = Maximum usable power gain of the receiver.
𝐵 =Noise equivalent bandwidth at the receiver.
𝑘𝐵 =Boltzmann constant, 1.38 ∗ 10−23 [𝐽𝐾−1].
The noise figure is the noise factor expressed in dB. If the
actual source has noise temperature of 𝑇0 at the input, the
maximum noise power at the output is given by
𝑁𝑜𝑢𝑡 = 𝐺𝑘𝐵𝑇0𝐵0 + 𝐺𝑘𝐵𝑇𝑅𝐵 (51)
which gives
𝑁𝐹 = 1 +𝑇𝑅
𝑇0
(52)
This expression only applied for particular terminating
impedance at the receiver input. All matter emits radiant
energy, when picked by an antenna; this radiation is
superimposed on the usable signal as background noise. If
𝑁0 is the power spectral density of such noise (expressed in
watt/Hz) the antenna temperature (expressed in Kelvin) is
such that:
𝑁0 = 𝑘𝐵𝑇𝐴 (53)
The antenna temperature is affected by:
The temperature and absorbance of external radiators.
The antenna gain and its orientation relative to these
external radiators.
In cascade subsystems of two stages the noise factor is related
to the noise temperatures by following formula
𝑁𝐹 = 𝑁𝐹1 +𝑁𝐹2 − 1
𝐺1
(54)
then
𝑇 = 𝑇1 +𝑇2
𝐺1
(55)
From these relationships, note that if the gain of the first
stage is sufficiently high, (particularly relevant in low-noise
receiving system were the first stage is low noise amplifier
LNA and the second stage the microwave receiver) the first
stage essentially sets the overall system noise performance.
The existence of a layer (like plasma) having power loss L
can seriously degrade system noise temperature. The system
noise temperature is
𝑇 = 𝑇𝐿𝑁𝐴 + 1 − 𝜂𝐴 𝑇0 + 𝜂𝐴 𝑇𝐴 1 − 𝐿 + 𝑇𝐿𝐿 (56)
where
𝑇𝐿𝑁𝐴 = Antenna radiation efficiency (0 ≤ 𝜂𝐴 ≤ 1)
𝑇𝐿 = Physical temperature of the plasma layer (°𝐾)
𝐿 = Noise temperature of LNA
𝜂𝐴 = Plasma power transmission loss factor (0 ≤ 𝐿 ≤ 1)
III. COMPUTATIONAL RESULT
The isotropic plasma may be considered as dielectric
media or conductive media depending on the propagating
frequency value with respect to plasma and collision
frequency. Fig. 2 represents the boundary between
conductive and dielectric plasma.
A propagating frequency 2.1 GHz is taken as interested
frequency, this frequency is used in TT&C space system, in
calculating the plasma parameters 휀′ and t𝑎𝑛𝛿 . Table II
illustrate the values at three plasma frequencies 0.5, 1.0 and 2
GHz. The contribution effect of collision frequency on these
parameters are demonstrated in the table via five values of
collision frequencies (𝑣𝑐=0, 0.2, 2.0, 4.0 and 8.0 GHz).
The skin depth parameter Pp is computed since the
plasma has conductive properties. Fig. 4 shows the variation
of Pp (m) for multi plasma frequencies (fp= 1.0, 2.0, 5, 10
and 15 GHz) since all calculations are taken in collision
frequency equal to 1 GHz. The loss parameter 𝑡𝑎𝑛𝛿 is
computed at propagating frequency 2.15 GHz for deferent
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Volume 3, Issue 2, August 2013
125
Table II: Plasma dielectric constants at 2.1 GHz at different
plasma and collision frequency.
Plasma
Frequency
[GHz]
Collision
Frequency
[GHz]
Real
relative 𝜺′
of Plasma
𝐭𝐚𝐧 𝜹 of
Plasma
0.5 0 0.9438 0
1.0 0 0.7732 0
2.0 0 0.0933 0
0.5 0.2 0.9438 0.0057
1.0 0.2 0.7753 0.0276
2.0 0.2 0.1011 0.8466
0.5 2.0 0.9703 0.0292
1.0 2.0 0.8811 0.1285
2.0 2.0 0.5240 0.8638
0.5 4.0 0.9878 0.0236
1.0 4.0 0.9500 0.0981
2.0 4.0 0.8040 0.4643
0.5 8.0 0.9963 0.014
1.0 8.0 0.9854 0.0565
2.0 8.0 0.9415 0.2366
plasma frequencies (fp= 2.0, 2.05, 2.10 and 2.125 GHz),
with respect to collision frequency as mentioned in Fig. 5.
While this 𝑡𝑎𝑛𝛿 parameter is computed, at same
propagating frequency f another plasma frequencies
(fp= 2.5, 4.0 and 8.0 GHz) as shown in Fig. 6. The absorption parameter α (Neper/m) at propagating
frequency 2.15 GHz is computed for many plasma
frequencies (fp= 2.15, 2.0, 1.5 and 1.0 GHz) with respect to
collision frequency as illustrated in Fig. 7. The absorption
parameter α (dB/m) is computed for the same variables and
drawings as in Fig. 8.
The phase constant β (radian/m) at propagating
frequency 2.15 GHz is calculated for many plasma
frequencies (fp=2.15, 2.0, 1.5, 1.0 and 0.5 GHz) with
respect to collision frequency as illustrated in Fig. 9. For a
single patch microstrip antenna, the well-known work
published by Lo [9, 11] was studied where the experimental
data of impedance locus and the radiation pattern were in
good agreement with the theory. The patch has the
dimensions of 11.43cm x 7.62cm and fed with a 50
coaxial probe at resonance frequency of 1187 MHz
operating with (0, 1) transverse magnetic TM01 mode. This
work has been investigated with the aid of MW-Office
package. The antenna was simulated in such a way that the
package conditions were: (a) the number of divisions=64,
(b) the division cell size was x=0.714cm, y=0.476cm, and
(c) the top dielectric layer of the enclosure was set to have
the properties of air with 2 cm in thickness; the antenna was
Fig. 4. The computational skin depth at different plasma
frequency.
Fig. 5. The tan loss of plasma as a function of collision frequency
for plasma frequencies blow and near propagating frequency
2.15 GHz.
fed with excitation port of 50 . There is good agreement
between the computed and the published results [6]. The
radiation pattern for both E and E in the same operating
(0, 1) mode has been computed for each of the two cuts,
=0 Fig. 9(a) and =90 Fig. 9(b). It is seen that there is
excellent agreement between the published radiation
patterns of the two cuts one as shown in Fig. 9(c) and Fig.
9(f), respectively.
Accordingly, the MW-Office package is used to design
rectangular microstrip patch antenna of dimensions of 4.96
cm x 3.3 cm printed on dielectric substrate (εr=4.45 and
𝑡𝑎𝑛𝛿 =0.0005) of thickness 1.6 mm and fed with a 50
coaxial probe at resonance frequency of 2.15 GHz operating
with (0, 1) transverse magnetic mode TM01. Some antenna
characteristics, the input impedance, VSWR and radiation
pattern are shown in Fig. 10.
For space application when cold plasma is generated
around spacecraft or space launcher the GPS or TT&C
antenna required ceramic cover to protect the conformal
antenna. A ceramic layer of 1 and 2 mm is tested when it
support directly above the patch antenna. The input
impedance of TM01 mode single rectangular patch operating
108
109
1010
1011
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0Attenuation by collissional absorbtion at radiating Freq =2.15GHz
Collision Frequency,Hz
tan d
elta
plasma frequency
=2.0GHz
=2.05 GHz
=2.10 GHz
=2.125GHz
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Volume 3, Issue 2, August 2013
126
0
-45
-90
-135
180
135
90
45
Mag Max
1
Mag Min
0
0.25
Per Div
E_Theta[0,1] E_Theta[90,1]
0
-45
-90
-135
180
135
90
45
Mag Max
1
Mag Min
0
0.25
Per Div
E_Phi[0,1] E_Phi[90,1]
Fig. 6. The tan loss of plasma as a function of collision frequency
for plasma frequencies above propagating frequency 2.15 GHz.
Fig. 7. Absorption coefficient as a function of collision
frequency for plasma frequencies above propagating
frequency 2.15 GHz.
Fig. 8. Phase shift in plasma as a function of collision frequency
for plasma frequencies below propagating frequency 2.15 GHz.
(a) (b)
(c) (d)
Fig. 9. Radiation patterns (E ( =90) and E ( =0)) for
published [12] and calculated results for TM01 mode of a
rectangular microstrip antenna with W=11.43 cm, L=7.62 cm
operating at resonance frequency 1.187GHz. (a) Published E,
(b) calculated E, (c) published E and (d) calculated E .
(a) (b)
(c) (d) Fig. 10. The input impedance (a), VSWR (b) and radiation
pattern E- and H-plane (c) and (d) of TM01 mode single
rectangular patch operating 2.15 GHz resonance frequency,
(patch size 4.96 cm x 3.3 cm, substrate thickness=1.6 mm,
𝜺𝒓=4.45 and 𝒕𝒂𝒏𝜹=0.0005).
at 2.15 GHz resonance frequency, (patch size
4.96 cm×3.3 cm, substrate thickness=1.6 mm, 휀𝑟=4.45 and
𝑡𝑎𝑛𝛿 =0.0005), and when the patch is covered ceramic
layer of 휀𝑟 =5.2 and 𝑡𝑎𝑛𝛿 =0.002 for thickness. Results
illustrates that there is no big changes with essential antenna
as shown in Fig. 11.
108
109
1010
1011
-80
-60
-40
-20
0
20
40
60
80
100Attenuation by collissional absorbtion at radiating Freq =2.15GHz
Collision Frequency,Hz
tan d
elta
Plasma frequency
=2.5 GHz
=4.0 GHz
=8.0 GHz
108
109
1010
1011
0
2
4
6
8
10
12
14
16Attenuation by collissional absorbtion at radiating Freq =2.15GHz
Collision Frequency,Hz
Alp
h [
neper/
mete
r]
Plasma Frequency
=2.15 GHz
=2.00 GHz
=1.50 GHz
=1.00 GHz
108
109
1010
1011
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5Attenuation by collissional absorbtion at radiating Freq =2.15GHz
Collision Frequency,Hz
Beta
[ra
d/m
ete
r]
Plasma frequency
=2.15 GHz
=2.00 Ghz
=1.50 GHz
=1.00 GHz
=0.50 Ghz
2 2.05 2.1 2.15 2.2
Frequency (GHz)
-20
0
20
40
60
Re
al
an
d I
ma
gin
ary
of
Z (
oh
m)
Re(Z[1,1]) ~
Im(Z[1,1]) ~
2 2.05 2.1 2.15 2.2
Frequency (GHz)
0
2
4
6
8
10
12
14
16
18
20
VS
WR
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Volume 3, Issue 2, August 2013
127
2 2.05 2.1 2.15 2.2
Frequency (GHz)
-20
0
20
40
60
Re
al
an
d I
ma
gin
ary
of
Z (
oh
m)
Re(Z[1,1]) ~
Im(Z[1,1]) ~
2 2.05 2.1 2.15 2.2
Frequency (GHz)
-10
0
10
20
30
Re
al
an
d I
ma
gin
ary
of
Z (
oh
m)
Re(Z[1,1]) ~
Im(Z[1,1]) ~
2 2.05 2.1 2.15 2.2
Frequency (GHz)
-20
-10
0
10
20
30
Re
al
an
d I
ma
gin
ary
of
Z (
oh
m)
Re(Z[1,1]) ~
Im(Z[1,1]) ~
(a) (b) (c) Fig. 11. The input impedance of TM01 mode single rectangular
patch operating 2.15 GHz resonance frequency, (patch size 4.96
cm x 3.3 cm, substrate thickness=1.6 mm, 𝜺𝒓=4.45 and
𝒕𝒂𝒏𝜹=0.0005), and when the patch is covered ceramic layer of
𝜺𝒓=5.2 and 𝒕𝒂𝒏𝜹=0.002 for thickness (a) 1mm, (b) 2mm and (c)
3mm.
(a) (b)
(c) (d) Fig. 12. The input impedance of TMo1 mode single rectangular
patch operating 2.15 GHz resonance frequency, (patch size 4.96
cm x 3.3 cm, substrate thickness=1.6 mm, 𝜺𝒓=4.45 and
tanδ=0.0005) with thin air layer of thickness=5 mm at (a)
𝒕𝒂𝒏𝜹=0, (b) 𝒕𝒂𝒏𝜹=0.005, (c) 𝒕𝒂𝒏𝜹=0.05 and (d) 𝒕𝒂𝒏𝜹=0.5
To explain the effect of dielectric plasma existence near
patch antenna, we simulate this plasma as a thin air layer has
a dielectric constant contain an imaginary part correspond to
the collision frequency in plasma conditions. The input
impedance of TM01 mode of single rectangular patch
operating at 2.15 GHz resonance frequency, (patch size of
4.96𝑐𝑚 × 3.3 𝑐𝑚, substrate thickness=1.6 mm, 휀𝑟 =4.45 and 𝑡𝑎𝑛𝛿 =0.0005) with thin air layer of thickness=5
mm at tanδ=0, 0.005, 0.05 and 0.5 is shown in Fig. 12. A
high collision simulated plasma (𝑡𝑎𝑛𝛿 = 0.5) is taken in
two different thicknesses 5.0 mm and 10 mm to compute the
input impedance of the antenna. Results are shown in Fig.
13 which shows that the high thickness gives very little
differences in both resistive and reactive element. Another procedure of simulation is used to study the
plasma effect on microstrip antenna. By designing TM01
mode single rectangular patch operating at 2.15 GHz
resonance frequency when the dielectric substrate is air (
dielectric plasma) has a sensitive loss factor (collision
frequency). Computations are done for 𝑡𝑎𝑛𝛿 = 0, 0.005,
0.05 and 0.5. At resonance patch size 10.46 𝑐𝑚 𝑥 6.97 𝑐𝑚
for air substrate thickness=1.6 mm. The input impedance cal
(a) (b) Fig. 13. The input impedance of TMo1 mode single rectangular
patch operating 2.15 GHz resonance frequency, (patch size
4.96 cm x 3.3 cm, substrate thickness=1.6 mm, 𝜺𝒓=4.45 and
tanδ=0.0005) with thin air layer of 𝒕𝒂𝒏𝜹=0.5 thickness (a) 5 mm
and (b) 10 mm.
(a) (b)
(c) (d) Fig.14. The smith chart input impedance of TM01 mode single
rectangular patch designed to operating at 2.15 GHz resonance
frequency, (patch size 10.46 cm x 6.97 cm, substrate
thickness=1.6 mm, 𝜺𝒓=1 and (a) 𝒕𝒂𝒏δ=0, (b) 𝒕𝒂𝒏𝜹=0.005, (c)
𝒕𝒂𝒏δ=0.05 and (d) 𝒕𝒂𝒏𝜹=0.5).
culations are illustrated in Fig. 14. Results shows that the
t𝑎𝑛𝛿 increases highly affect the values of both the reactive
and resistive impedance. The effect amount is clearly
explained in Fig. 14(b).
Because of the MW-Office package limitations on taking
substrate of dielectric constant (휀𝑟 < 1), a cavity model is
used. A MATLAB algorithm is programmed according to
the theory that mentioned in the previous section. The input
impedance of TM01 mode of single rectangular patch
designed to operating at 2.15 GHz resonance frequency,
(patch size of 10.46𝑐𝑚 × 6.97 𝑐𝑚, substrate thickness=1.6
mm, tanδ=0.0005) at different plasma simulated values of
휀𝑟=1, 0.8, 0.6, 0.4, 0.2, 0.1 and 0.05 are computed and
demonstrated in Fig. 15. An important mentioned result for
this trial is the bandwidth enhancement with the lower
dielectric value is achieved.
0 1.0
1.0
-1.0
10.0
10.0
-10.0
5.0
5.0
-5.0
2.0
2.0
-2.0
3.0
3.0
-3.0
4.0
4.0
-4.0
0.2
0.2
-0.2
0.4
0.4
-0.4
0.6
0.6
-0.6
0.8
0.8
-0.8
Swp Max
2.2GHz
Swp Min
1.9GHz
0 1.0
1.0
-1.0
10.0
10.0
-10.0
5.0
5.0
-5.0
2.0
2.0
-2.0
3.0
3.0
-3.0
4.0
4.0
-4.0
0.2
0.2
-0.2
0.4
0.4
-0.4
0.6
0.6
-0.6
0.8
0.8
-0.8
Swp Max
2.2GHz
Swp Min
1.9GHz
0 1.0
1.0
-1.0
10.0
10.0
-10.0
5.0
5.0
-5.0
2.0
2.0
-2.0
3.0
3.0
-3.0
4.0
4.0
-4.0
0.2
0.2
-0.2
0.4
0.4
-0.4
0.6
0.6
-0.6
0.8
0.8
-0.8
Swp Max
2.2GHz
Swp Min
1.9GHz
0 1.0
1.0
-1.0
10.0
10.0
-10.0
5.0
5.0
-5.0
2.0
2.0
-2.0
3.0
3.0
-3.0
4.0
4.0
-4.0
0.2
0.2
-0.2
0.4
0.4
-0.4
0.6
0.6
-0.6
0.8
0.8
-0.8
Swp Max
2.2GHz
Swp Min
1.9GHz
0 1.0
1.0
-1.0
10.0
10.0
-10.0
5.0
5.0
-5.0
2.0
2.0
-2.0
3.0
3.0
-3.0
4.0
4.0
-4.0
0.2
0.2
-0.2
0.4
0.4
-0.4
0.6
0.6
-0.6
0.8
0.8
-0.8
Swp Max
2.1GHz
Swp Min
1.95GHz
0 1.0
1.0
-1.0
10.0
10.0
-10.0
5.0
5.0
-5.0
2.0
2.0
-2.0
3.0
3.0
-3.0
4.0
4.0
-4.0
0.2
0.2
-0.2
0.4
0.4
-0.4
0.6
0.6
-0.6
0.8
0.8
-0.8
Swp Max
2.1GHz
Swp Min
1.95GHz
0 1.0
1.0
-1.0
10.0
10.0
-10.0
5.0
5.0
-5.0
2.0
2.0
-2.0
3.0
3.0
-3.0
4.0
4.0
-4.0
0.2
0.2
-0.2
0.4
0.4
-0.4
0.6
0.6
-0.6
0.8
0.8
-0.8
Swp Max
2.1GHz
Swp Min
1.95GHz
2 2.05 2.1 2.15 2.2
Frequency (GHz)
-10
0
10
20
30
Re
al
an
d I
ma
gin
ary
of
Z (
oh
m)
Re(Z[1,1]) ~
Im(Z[1,1]) ~
2 2.05 2.1 2.15 2.2
Frequency (GHz)
-20
0
20
40
60
Re
al
an
d I
ma
gin
ary
of
Z (
oh
m)
Re(Z[1,1]) ~
Im(Z[1,1]) ~
2 2.05 2.1 2.15 2.2
Frequency (GHz)
-20
0
20
40
60
Re
al
an
d I
ma
gin
ary
of
Z (
oh
m)
Re(Z[1,1]) ~
Im(Z[1,1]) ~
ISSN: 2277-3754
ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT)
Volume 3, Issue 2, August 2013
128
(a)
(b)
Fig. 15. The input resistance (a) and input reactance (b) of TM01
mode of single rectangular patch designed to operate at 2.15
GHz resonance frequency, (patch size of 10.46cm x 6.97 cm,
substrate thickness=1.6 mm, 𝒕𝒂𝒏𝜹 =0.0005) for different
plasma simulated values of 𝜺𝒓=1, 0.8, 0.6, 0.4, 0.2, 0.1 and 0.05.
IV. CONCLUSION
The plasma generation around antenna in space system is an
important subject must be considered in primary design
stages. Normal system measurements are taken in the
laboratory and may be a free space atmosphere is available
to adjust and tuning the front end of the antenna. In plasma
condition this adjustment is not enough since the plasma
change the input impedance. So that we suggest two
antennas system must be used as a redundancy system to
overcome such problem. The existence of collision plasma
absorbs microwave energy depending on plasma thickness
and density distribution. The plasma effects open very
important window on TT&C and GPS antennas which now
a days are widely used. Finally this report give the essential
windows in plasma affect on antenna system for continuous
researches in different actual importance in this field.
REFERENCES
[1] K.-F. Lee, and K.-F. Tong, "Microstrip patch antennas-basic
characteristics and some recent advances", Proceedings of the
IEEE, Vol. 100, No. 7, July 2012.
[2] D. Guha and Yahia M. M. Antar, Microstrip and Printed
Antennas New Trends, Techniques and Applications, New
York; John Wiley & Sons, Ltd, 2011.
[3] Chen, F.F., Introduction to plasma physics, Plenum press, New
York, 1974.
[4] Frankel D.S., et al "Re entry plasma induced pseudo range and
attenuation effects in a GPS simulator", SPIE defense and
security symposium, Orlando, FL, SPIE proceeding 5420
(12-16 April 2004). Downloaded from the physical science
incorporation library.
[5] Drabowitch, S. and Anaconna C. "Antennas Volum2
Applications", Hemisphere publishing corporation, 1988.
[6] Y. T. Lo, D. Solomon and W. F. Richards “Theory and
experiment on microstrip antennas,” IEEE Trans. on Antennas
and Propag., vol. AP 27, no. 2, pp. 137-145, 1979.
[7] I.J. Bahl and P. Bhartia, Microstrip Antennas, Artech House,
Inc. printed and bound in the U.S. A, 1980.
[8] Andersg G. Derneryd, and Anders G. Lind, “Extended analysis
of rectangular microstrip resonator antennas”, IEEE Trans. on
Antennas and Propag., vol. AP-27, no.6, pp. 846-849, Nov.
1979.
[9] J. R. James and P. S. Hall, “Handbook of Microstrip
Antennas,” Peter Peregrinus Ltd, London, 1989.
[10] Gildas P. Gauthier and Gabriel M. Rebeiz, “Microstrip
antennas on synthesized low dielectric-constant substrates,”
IEEE Trans. on Antennas and Propag., vol. 45, no. 8, pp.
1310-1313, Aug. 1997.
[11] Keith R. Carver and James W. Mink, “Microstrip antenna
technology,” IEEE Trans. on Antennas and Propag.", vol.
AP-29, no.1, pp. 2-23, 1981.
[12] P. Hammer, D. Van Bouchaute, D. Verschraeven, and A. Van
De Capelle. "A model for calculating the radiation field of
microstrip antennas", IEEE Trans. on Antennas and Propag.,
vol. 27, no.2, pp 267-270, Mar. 1979.
[13] Kokako, D.J. "Analysis of radome-enclosed antennas" Artech
house, 1997.
[14] Maral,G. and Bousquat, M. "Satellite Communications
Systems ", John Wiley & Sons, 1980.
AUTHOR BIOGRAPHY
Abdulkareem A. A. Mohammed was born in AL
Nassiria, Iraq, in 1958. He received his BSc in electrical engineering (1980) from Sulaimania
University, Sulaimania, Iraq, postgraduate diploma
in communications (1982) and MSc in communication (1984) from the University of
Technology, Baghdad, Iraq. From 1984 to 1988 he
was working with the Electromagnetic Wave Propagation Department, Space and Astronomy
Research Center, Scientific Research Council,
Baghdad, Iraq. From 1988 to 1993 he was working with the Space
Technology Department, Space Research Center, Baghdad, Iraq. On 1994,
he joined the Physics department, college of science, Saddam University,
Baghdad, Iraq where he obtained his PhD (1997) in electromagnetic, microstrip microwave antennas. From 1997 to 2003 he was working with the
1.5 2 2.5 3
x 109
-30
-20
-10
0
10
20
30Rectanguler microstrip antenna of plasma substrate
F(Hz)
Input
reacta
nce
Apsr=0.05
=0.10
=0.20
=0.40
=0.60
=0.80
=1.00
1.5 2 2.5 3
x 109
0
10
20
30
40
50
60Rectanguler microstrip antenna of plasma substrate
F(Hz)
Input
resis
tance
Apsr=0.05
=0.1
=0.2
=0.4
=0.6
=0.8
=1.0
ISSN: 2277-3754
ISO 9001:2008 Certified International Journal of Engineering and Innovative Technology (IJEIT)
Volume 3, Issue 2, August 2013
129
Al-Battany Space Directorate as a researcher and head of group in the field
of microwave system. Since 2004 he is the head of Space and Atmosphere
Research Center in Iraqi ministry of science and technology. Now he leads group of atmosphere remote sensing for dust storm monitoring and detection
by using different space tools. Since January 2011 he joined a post doctorate
in Systems Engineering Department, University Arkansas at Little Rock in the field of dust storm monitoring.
Dhirgham K. Naji was born in AL Nassiria, Iraq, in 1973. He received his BSc degree in Electrical
Engineering from Baghdad University, Baghdad,
Iraq, in 1995, and MSc degree in Communications Engineering from Baghdad University, Baghdad,
Iraq, in 1998, and PhD degree in Modern
Communications Engineering from Alnahrain University, Baghdad, Iraq, in 2013. His current
research interests include fractal antennas, RFID
antenna miniaturization and Electromagnetic optimization.