S-band Shorted Patch Antenna for Inter Pico Satellite Communications

Abstract

In this paper we study and evaluate shorted patch and CPW-feed square slot antennas, both of which we deem suitable for use in inter pico satellite communications in terms of gain, bandwidth and size. We have simulated both antennas in the High Frequency Structure Simulator (HFSS). Our results show that the shorted patch antenna achieves higher gain; e.g., 4.8 dBi, wider impedance bandwidth; e.g., 3.9-11.1 GHz with Voltage Standing Wave Ratio (VSWR) ≤ 2 at resonance frequencies of 4.4, 6.9 and 10.1 GHz. In addition, the Quasi Newton method is used to shift the shorted patch antenna's operating frequency to 2.45 GHz (S-band). This thus enables its use in the unlicensed ISM band without critically affecting its radiation performance. The simulated results show an impedance bandwidth of 3650 MHz (2.05-5.7 GHz) with VSWR ≤ 2 at a resonance frequency of 2.45 GHz.

Full text

S-band Shorted Patch Antenna for Inter Pico Satellite
Communications
Faisel Em Tubbal
Raad Raad
Kwan-Wu Chin
Brenden Butters
School of Electrical, Computer and Telecommunications Engineering
University of Wollongong, Northfields Ave, NSW, Australia, 2522
femt848@uowmail.edu.au, raad@uow.edu.au, Kwanwu@uow.edu.au, bab900@uowmail.edu.au.
Abstract—In this paper we study and evaluate shorted patch and
CPW-feed square slot antennas, both of which we deem suitable
for use in inter pico satellite communications in terms of gain,
bandwidth and size. We have simulated both antennas in the
High Frequency Structure Simulator (HFSS). Our results show
that the shorted patch antenna achieves higher gain; e.g., 4.8 dBi,
wider impedance bandwidth; e.g., 3.9-11.1 GHz with Voltage
Standing Wave Ratio (VSWR) ≤ 2 at resonance frequencies of
4.4, 6.9 and 10.1 GHz. In addition, the Quasi Newton method is
used to shift the shorted patch antenna’s operating frequency to
2.45 GHz (S-band). This thus enables its use in the unlicensed
ISM band without critically affecting its radiation performance.
The simulated results show an impedance bandwidth of 3650
MHz (2.05-5.7 GHz) with VSWR ≤ 2 at a resonance frequency of
2.45 GHz.
Keywords— cross link; pico-satellites; cubesat; cavity backed.
I. INTRODUCTION
Pico satellites operate at Low Earth Orbit (LEO) at altitudes
of 200 to 600 km and remain in the same orbit for a few weeks
before Earth’s weak ionosphere causes them to lose altitude.
They have a mass ranging from 0.1 to 1 kg [1]. Compared with
conventional satellites, they are an order of magnitude cheaper,
consume less power, and are easier to construct. A typical
example of pico-satellites is CubeSat, which has a weight
ranging from 1.3 to 6 kg. All cube satellites have a fixed face
size of 10cm×10cm with three different depth dimension
configurations: 10cm (1U), 20cm (2U), and 30cm (3U) [2].
Fig. 1 illustrates a typical example of a 10-cm CubeSat (1U)
with a mass of 1 kg. A key advantage of pico-sats is their
potential ability to form a collaborative swarm that covers large
geographical areas, and to increase contact time with ground
stations [3, 4].
Fig. 1. 1U cube satellite (10cm×10cm×10cm) [5]
A critical component of pico-satellites that enables
efficient swarm formation is the cross link communication
antenna [6-8]. However, the limited real estate, power (≤ 2
W), and communication opportunities (1.2 – 9.6 kbit/s) of
pico-satellites pose real challenges to any antenna designs.
Specifically, designs are required to meet the size and weight
restrictions of pico-satellites while yielding high gain with low
power consumption. The latter is particularly critical as it
reduces battery power consumption and hence, reduces the
overall battery weight and size of a pico-satellite. Moreover,
any radio used must have a low output power; e.g., 2W.
To date, existing works on antenna designs for pico
satellites include novel quad-polarization agile patch antennas
[9], low-profile circularly polarized cavity-backed antennas
using HMSIW technique [10], CPW-feed square slot antenna
with lightening-shaped feed line for broadband circularly
polarized radiation[11], and enhanced bandwidth shorted
patch antennas using folded-patch techniques [12]. All these
designs achieve gain ranging from 4 to 5 dBi, and antenna
physical size ranging from 1.8x1.5 to 6x6 cm2. Their
operating frequency range is 3 to 8.8 GHz. Amongst the many
designs, only two designs address the stated design
requirements of pico satellites; namely, [12] and [11]. In [11],
Laio and Chu propose a CPW-feed square slot antenna with
lightening-shaped feed line. The total size of the antenna is
6×6 cm2 which is fabricated on a FR4 substrate having
thickness 0.08cm. A coplanar Wave Guide (CPW) feed line
978-1-4799-7447-4/14/$31.00 ©2014 IEEE

technique is used with a fixed width of a si
n
cm and the distance of the gap between th
plane is 0.03 cm in order to achieve 50
Ω
shaped feed line and the embedded F-shap
e
enhance and enlarge the Axial Ratio (AR)
proposed antenna. More details on [11]
presented in Section III.
A key limitation to date is that no w
o
designs [12] and [11] on a common platfor
m
have studied both designs using the High F
r
Simulator (HFSS) [13] to compare their
pe
the same environment. The design of [11]
s
impedance bandwidth of 290 MHz (3.08 t
o
VSWR ≤ 2. It also achieved a simulated g
a
return losses (S
11
) of -28.6 and -19.7
frequencies 3.2 and 3.8 GHz respectively.
design of [11], the design of [12] has a muc
h
i.e., 7200 MHz (3.9 to 11.1 GHz), a higher
and a smaller antenna size; i.e., 3x3 cm
2
. H
o
in [12] does not operate in the 2.45 G
H
resonance frequencies are 4.4, 6.95 and 10.
0
bands). This is an important consideratio
n
the antennas for
p
ico satellites are designed
t
2.5 GHz unlicensed Industrial, Scientific a
n
b
and, meaning the end user is not r
e
government permit to use the antenna. To t
h
superior performance of the design reported
i
section, we first present the shorted patch a
n
and the required improvements to shift its o
p
from 4.4 GHz (C-
b
and) to 2.45 GHz
critically effecting its performance.
II.
SHORTED PATCH ANTENNA REPU
Fig. 2 shows a simulation model of
t
antenna [12]. It consists of upper and l
o
dimensions of 1.8×1.5 and 0.75×0.65 cm
2
r
e
p
atches are connected together via a folded
Also, they are connected to a 3×3 cm
2
gro
u
shorting pins and probe feed. Moreover,
short probe length, it uses the air substra
t
ramp-shaped part. This leads to a decrea
s
factor (Q) and the inductive reactance of th
e
enhancement of the bandwidth. The main
shorting pins at the edges of the upper p
a
miniaturization at wide impedance bandwid
t
centre pin at the upper patch is used to broa
d
bandwidth
b
y generating resonances at 4.4 a
n
n
gle strip; i.e., 0.42
e line and ground
Ω
matching. The
e
d slits are used to
bandwidth of the
and [12] will be
o
r
k
has compared
m
. Therefore, we
r
equency Structure
e
rformance within
s
hows a simulated
o
3.37 GHz) with
a
in of 3.8 dBi and
dB at resonance
Compared to the
h
wider bandwidth;
gain; i.e., 4.8 dBi
o
wever, the design
H
z (S-band) as its
0
5 GHz (C and X
n
because
m
ost of
t
o work in the 2.4-
n
d Medical (ISM)
e
quired obtain a
h
is end, due to the
in
[12], in the next
n
tenna design [12]
p
erating f
r
equency
(S-band) without
RPOSING
t
he shorted patch
o
wer patches with
e
spectively. These
ramp-shaped part.
u
nd plane through
in order to use a
t
e and the folded
s
e in both quality
e
probe and he
n
ce
purpose of using
a
tch is to achieve
t
h. In addition, the
d
en the impedance
n
d 6.95 GHz.
Fig. 2. Geometry of shorted patch ant
e
The aforementioned shorte
d
at 4.4 GHz. Hence a frequenc
y
patch antenna design in [12]
band (2.45 GHz). A frequenc
y
the size of the antenna. How
e
maximum size and weight of t
h
[13], the antenna was
a
Specifically, in order to optimi
z
2.45 GHz, the Quasi Newt
o
available in the simulator) [1
4
works on the basis of finding
t
cost function by varying the v
a
In our case, the decision varia
b
dimensions with range 0.6
5
(maximum). The aim is to
a
(design parameter) at opera
t
(constraint). Therefore, the Q
u
the value of return loss (S
11
)
100 times (iterations) from 0
.
and maximum step sizes of 0.
The results show that the ante
n
factor of 1.3 mm to achieve a
m
at an operating frequency of 2.
4
III.
EVA
L
A. A Comparison of Shorted
P
Square Slot Antenna
We first
p
rovide a compara
t
in terms of return loss, Voltag
e
b
andwidth, gain and antenna
s
VSWR and return loss of the
within a frequency range of 2-
operates at frequencies of 3.2
a
lower than the original sho
antenna’s resonance frequenci
e
(X-bands). We see that the s
h
e
nna [12]
d
patch antenna design operates
y
shift is required for the shorted
in order for it to operate in S-
y
shift is possible by increasing
e
ver, we are also limited by the
h
e CubeSat. Hence using HFSS
a
ppropriately re-dimensioned.
z
e for an operating frequency of
o
n method was used (this is
4
]. The Quasi Newton method
t
he minimum or maximum of a
a
riables to meet the constraints.
b
le is the length of the antenna’s
5
3 (minimum) to 1.959 mm
a
chieve a minimum return loss
t
ing frequency of 2.45 GHz
u
asi-Newton method minimizes
by varying the antenna lengths
.
653 to1.959 mm by minimum
013 and 0.13 mm respectively.
n
na size must be increased by a
m
inimum return loss of -27.6 dB
4
5 GHz.
L
UATION
P
atch Antenna and CPW-Feed
t
ive study between [11] and [12]
e
Standing Wave Ratio (VSWR),
s
ize. Fig. 3 and 4 compare the
shorted patch and slot antennas
12 GHz. The CPW-slot antenna
a
nd 3.8 GHz (S-band), which is
rted (describe in [12]) patch
e
s; i.e., 4.4, 6.9 and 10.1 GHz
h
orted patch antenna achieves a

wider bandwidth than the CPW-slot antenna at VSWR ≤ 2.
Moreover, as shown in Table I, the shorted patch antenna has a
smaller size, and a higher gain. This is important for pico-
satellites as it provides more space for solar cells and the higher
gain provides longer communication distance and therefore
decreases the number of pico-sats used in a swarm.
Fig. 3. VSWR of shorted patch and CPW-Fed slot antennas
Fig. 4. Return loss of shorted patch and CPW slot antennas
TABLE I. A COMPARISON OF SHORTED PATCH AND SLOT
ANTENNAS
Frequencies
[GHz]
VSWR
[dB]
BW
[GHz]
Gain
[dB]
Size
[cm2]
Shorted
Patch
Antenna[12]
4.4, 6.9 and
10.1
1.11,
1.25
and
1.13
3.9-
11.1
4.8 3×3
CPW-Fed
Square Slot
Antenna[11]
3.2 and 3.8 0.64
and 1.8
3.05-
3.39
3.8 6×6
B. Re-dimensioning of The Shorted Patch and CPW-Fed
Square Antennas
We now show the results for the re-dimensioned antennas.
Fig. 5 and 6 show the VSWR and return losses of the 4.4 and
2.45 GHz shorted patch antennas. We see that the resonance
frequency of both modified antennas has been shifted to 2.45
GHz. The new antennas have only one resonance frequency at
2.45 GHz. As shown in Fig. 5, the re-dimensioned shorted
patch antenna achieves an impedance bandwidth of 3650 MHz
(2.05-5.7 GHz) with VSWR ≤ 2 while the re-dimensioned
CPW-fed square slot antenna achieves smaller bandwidth of
450 MHz (2.25-2.70 GHz) with VSWR ≤ 2. The simulated
return loss curves are shown in Fig. 6. Hence, the re-
dimensioned shorted patch and CPW-fed square slot antennas
have return losses of -27.6 and -25.13 dB respecteively.
Critically, this is simliar to the return loss of the original
designs of [12] and [11] at 4.4 and 3.2 GHz respecively.
Compared with the re-dimensioned CPW-fed square slot
antenna, as set out in Table II, the re-dimensioned shorted
patch antenna has a higher gain and wider bandwidth.
Therefore, the re-dimensioned shorted patch antenna is more
suitable for inter pico satellite communications that works at
S-band; e.g., 2.45 GHz. The main limitation of this
improvement is the reduced gain. However, it still meets the
antenna design requirements for inter pico satellite
communications. An immediate future work is to apply gain
enhancement techniques such as the cavity-backed model of
[15] to increase directivity and improve gain.
Fig. 5. VSWR of shorted patch and CPW-fed slot antennas
Fig. 6. Return loss of shorted patch and CPW-fed slot antennas
Figs. 7 and 8 show the simulated radiation patterns of the
re-dimensioned shorted patch and CPW-Fed square slot
antennas. Fig. 7 shows that the radiation pattern of shorted

patch is more uniform than that of CPW-Fed square slot
antenna.
Fig. 7. Total Gain of re-dimensioned shorted patch antenna at 2.45 GHz
Fig. 8. Total gain of re-dimensioned CPW-fed slot antenna at 2.45 GHz
TABLE II. RETURN LOSS, VSWR, BW, GAIN AND SIZE
Frequencies
(GHz)
VSWR
(dB)
BW
(GHz)
Gain
(dB)
Size
(cm2)
Shorted Patch
Antenna
4.4, 6.9 and
10.1
1.11, 1.25
and 1.13
3.9-11.1 4.8 3×3
Modified
Shorted Patch
Antenna
2.45 1.38 2.05-5.7 3.51 8.3×8.3
Modified
CPW-Fed Slot
Antenna
2.45 0.96 2.25-2.7 1.53 7.5×7.5
IV. CONCLUSION
We have presented an improved shorted patch antenna for
inter pico satellite communications. Specifically, we have
used the quasi Newton algorithm technique to shift the
operating frequency from C-band (4.4 GHz) to S-band (2.45
GHz) without critically affecting the shorted patch antenna’s
radiation performance. This improved shorted patch antenna
has a resonance frequency of 2.45 GHz, and operates with a
bandwidth from 2.05 to 5.7 GHz at VSWR ≤ 2 and provides a
gain of 3.51 dB.
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