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3D Printed Horn Antenna with Ceramic Implant
for Microwave Breast Imaging
Ji Wu, Rui Wu, Xiaofeng Zhang, and Fan Yang*
Shenzhen ET Medical Technology Co., Ltd.
Shenzhen, China
wuji@et-group.cn, wr@et-group.cn, zxf@et-group.cn,
yf@et-group.cn
Huihai Wang, Zhenhua Hu, Lin Sun
Shenzhen Terahertz Technology Co., Ltd.
Shenzhen, China
whh@et-group.cn, hzh@et-group.cn, sl@et-group.cn
Abstract—We propose a new type horn antenna for
microwave breast tissue imaging. It presents compact size (20mm
×20mm), stable transmission coefficients, robust fidelity (>0.9 at
100mm) while maintaining low return loss (<－14dB) across
4.1GHz to 11GHz. Using 24 such antennas we developed a
hemispherical array for the breast tumor screening. We
demonstrated the proposed array using homogeneous tissue
mimicking breast phantom with a realistic dielectric contrast of
1.2:1.
Keywords—3D printing, microwave imaging, antenna
I. INTRODUCTION
Microwave radar based imaging for breast cancer detection
has been successfully implemented by various UWB imaging
systems [1]-[3]. In these systems, antenna is a key component
to transmit UWB signals into the breast tissues and receive
their backscattered responses. A number of antennas have been
reported in [4]-[10]. Li et al proposed a ridged pyramidal horn
with very low return loss across the operating UWB bandwidth
that works in both free space and coupling liquid [4]. Gibbins
et al [5] reported a wide-slot antenna with metallic cavity that
provides a compact size and better performance than their
previous patch antenna. However, it gave relatively low level
of transmission coefficient. Balanced antipodal Vivaldi antenna
with a dielectric director was presented in [6] which improved
the directivity and gain of Vivaldi antenna. A TEM horn
coupled with high dielectric material was proposed by Amineh
et al [7] to achieve a good match with breast tissues. This
antenna can directly touch the phantom without using coupling
liquid. However, it has low efficiency and suffers from
declined fidelity at increased distance.
In this paper we present a novel horn antenna with ceramic
implant. It is fed by SMA and uses modified Vivaldi flares that
are supported by four layers of dielectric substrates. With
ceramic implant, the antenna can be used when immersed in
coupling liquid such as in systems [2], [8] or directly to contact
the breast as applied in portable imaging system [9].
II. ANTENNA GEOMETRY
The geometry of the proposed antenna is shown in Fig. 1.
The antenna is 24mm long with aperture as small as 20mm ×
20mm. Three flares are connected to partitioned horn with 6
chip resistors. Four 200 ohm resistors are used to connect the
conductor (middle layer) with horn cavity to match the 50 ohm
impedance. The horn cavity and flares are fabricated by 3D
printed using titanium alloy (Ti-6AI-4V) as shown in Fig.1 (c).
Additional two 100 ohm resistors are used to connect the two
grounds (external layers) with horn cavity for better match
according to optimized FDTD simulations. The transition parts
of the three planes have constant width of 2mm. For the
convenience in fabrication we use the straight edges in flared
sections instead of curved shapes. Ceramic implant is
fabricated by 3D printed with average dielectric contrast of 9.6
over frequency from 1 GHz to 9 GHz. Normal Olive oil with
dielectric constant 2.6 at 7GHz is used as the coupling liquid
for antenna measurement.
III. ANTENNA PERFORMANCES
Return loss (S11) is illustrated in Fig.2(a). It can be
observed that both measured and simulated S11 reach low
levels up to 11GHz and match on the main trend. The
disagreement is due to antenna fabrication, as a small gap may
exists between ceramic implant and metallic flares. The values
of S21 in Fig. 2(b) are flat and stable closely at －25dB from
(a) (b)
(c) (d)
Fig. 1 Illustration of the proposed antenna design. (a) Top view. (b) Side
uview. (c) 3D printed antenna structure. (d) 3D printed ceramic implant .
The presented work was supported by the Shenzhen Science and
Technology Innovation Committee funds under Grant
JSGG20160427105120572, Grant JSGG20170413154603151 and Grant
GJHZ20180424173554166)
x
y
z
200 ohm
resistors
11
9
13
7 5.5
100 ohm
resistors
24
3
24
9
8 20
4 5 6 7 8 9 10 11 12 13
-40
-30
-20
-10
0
Freque ncy (GHz)
S11 (dB)
Measured
Simulated
2 4 6 8 10 12 14
-60
-50
-40
-30
-20
-10
Frequency (GHz )
S21 (dB)
Simulated
Measure d
Fig.2 (a) Measured and simulated S11; (b) Measured and simulated S21.
00.5 11.5
-2
-1
0
1
2
Time (ns)
Normalized Amplitude
Observed
Ideal
Fig. 3 Normalized radiated and ideal pulses at 100mm.
4.4GHz to 11GHz which are higher than antennas reported in
[5]. Fidelity is a key factor for time-domain imaging algorithm
as it measures how accurately the pulse is transmitted and
received by the antenna. As shown in Fig. 3, little distortion is
received as the fidelity can reach 0.94 that is higher than that
reported in [7].
IV. RADAR IMAGING
Fig. 4(a) shows our imaging system with an array of 24
proposed antennas. The phantom is fabricated using silica gel
with
T
ε
=
3.25 at 7GHz. The target uses oil droplet with
T
ε
=
2.65 at 7GHz and diameter of 10mm that forms a realistic
dielectric contrast of 1.2:1. The gap between phantom and
array is filled by coupling liquid using olive oil. Synthesized
UWB pulse is calculated by inverse Fourier transform of
frequency sweep from 1 to 9GHz by vector network analyzer
(Keysight P9372A). The array is rotating at multiple angles to
generate multistatic pulses. The whole scan takes 6 mins and
the image can be reconstructed in 1 min.
Antenna excitation and other unwanted artifacts are
removed by subtracting a twin signal that is obtained by
rotating the array at 10 degree. The image reconstruction
method uses space-time beamforming [10] that is capable to
(a) (b)
Fig. 4 (a)Imaging setup for tissue mimicking phantom.(b) Reconstructed
images on the system screen of embedded targets.
suppress interference effectively provided a rich signal
acquisition. We can observe in Fig. 4(b) that the maximum
intensity is focused accurately at this low dielectric contrast
scenario with only a slight clutter appearance.
V. CONCLUSION
In this paper we design a new UWB antenna with compact
size (20mm × 20mm) and high fidelity (>0.9). We have
demonstrated the antenna is capable to image in a low
dielectric contrast scenario (1.2:1) making it a good candidate
for microwave breast screening. This antenna can be used in
both radar and tomographic imaging that is more clinically
useful.
ACKNOWLEDGMENT
Authors appreciated Dr. Ming Yan and Dr. Shuoyuan Zhou
at Department of Materials Science and Engineering, Southern
University of Science and Technology, for the fabrication of
3D printed ceramic implant and antenna structure.
REFERENCES
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