Design of Narrow -wall Slotted Waveguide Antenna with V … · 2018. 10. 19. · Abstract - Slotted...
Transcript of Design of Narrow -wall Slotted Waveguide Antenna with V … · 2018. 10. 19. · Abstract - Slotted...
Design of Narrow-wall Slotted Waveguide
Antenna with V-shaped Metal Reflector for X-
Band Radar Application
Derry Permana Yusuf, Fitri Yuli Zulkifli, and Eko Tjipto Rahardjo Antenna Propagation and Microwave Research Group, Electrical Engineering Department, Universitas Indonesia
Depok, Indonesia
Abstract - Slotted waveguide antenna with wide bandwidth
characteristics is designed at the 9.4-GHz frequency (X-band) for radar application. The antenna design consists of 200 narrow-wall slots with novel design of V-shaped metal reflector
to enhance side lobe level (SLL) and gain. New optimized slot design results in SLL of -31.9 dB. The simulation results show 36.7 dBi antenna gain and 780 MHz bandwidth (8.67-9.45 GHz)
for VSWR of 1.5.
Index Terms — slotted waveguide antenna, X-band, narrow-wall slots, high gain, metal reflector, radar
1. Introduction
Radar is essential component used for detecting hazards
(such as coastlines, islands, icebergs, other objects or ships),
and assisting the navigator in making timely decisions. The
majority of VTS services use X-band radars as a best
compromise, especially since technologies for rain clutter
suppression have been matured. Also, as a result of
production volume, X-band radars are the least expensive.
Antenna system is used on many platforms such as ships,
ports, or surveillance tower need to be high gain with tightly-
controlled beamwidths, strong, compact, lightweight and
resistant to the effects of roll and motion. [1-3]. Low side
lobe level and high efficiencies antenna performance are also
required to fulfil the VTS equipment standards. Slotted
waveguide antennas can fulfil all of these criteria. Slotted
waveguide antennas (SWAs) [4] radiate energy through slots
cut in conducting broad or narrow wall of a rectangular
waveguide. These slots introduce discontinuities in the
conductor and interrupt the current flows along the
waveguide [1]. SWAs can be realized as resonant or non-
resonant according to the wave propagation inside the
waveguide (respectively standing or traveling wave).
In this paper, a slotted waveguide antenna is designed for
operation at X-band frequency (8 to 10 GHz). Its scanning
beam requires a narrow beamwidth in the azimuth plane and
wider beamwidth in the elevation plane to compensate for
the roll of the ship [3]. The discrete Taylor distribution was
chosen for the antenna system because of its good theoretical
match to side lobe level requirement. Later, two metal sheets
as metal reflector are attached to the SWA edges to focus its
azimuth plane beam. The reflection coefficient, radiation
pattern plots, and gain results of the antenna are reported.
2. Antenna Configuration
The 3-D view of the proposed antenna configuration is
shown in Fig 1. The antenna configuration consists of narrow
wall slot waveguide with V-shaped metal reflector. The
target frequency is 9.4 GHz. The slot antenna dimension
with its parameters is shown in Fig. 2. The antenna radiates
horizontal polarization and determines the parameters w =
1.58 mm and t = 1.25 mm. The antenna also has two
independent parameters to be optimized: d (depth of the slot)
and θ (slot inclination angle).
In this work, the design criteria are specified to fulfil the
IALA V-128 Recommendations for minimum first lobe side
lobe level suppression of 26 dB and 33 dB at 10 degree or
more outside the main lobe [5]. Those requirements are
recommended for Basic level of VTS radar type. Other
parameters are also specified to be less than 22° for vertical
half-power beamwidth, less than 0.5° for horizontal half-
power beamwidth, cross-polarization < -25 dB, and front-to-
back ratio >30 dB. Similarly, 200 number of slots and
optimal slot spacing of 0.7λ are employed to achieve the
requirements of -30 dB SLL and horizontal half-power
beamwidth < 0.5°. V-shaped metal reflector is employed and
proposed as the design innovation in order to enhance the
antenna gain and achieve desired beamwidth for radiation
pattern.
By using (1):
single 2 2
180+3log 3log dBGain Gain n
(1)
Where Gainsingle is the gain of a single slot. In this paper,
gain of single antenna slot (Gainsingle) ~ 5dB, n = 200, and
Fig. 1. Full 3D view of X-band slotted waveguide antenna
with V-shaped metal reflector configuration
Fig. 2. Antenna dimension with its parameters
2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea
[ThE2-5]
265
with ϕ = 30° results in gain of 35.7 dB which is satisfied to
meet the Basic level of specifications for marine radar.
3. Antenna Synthesis
A finite percentage of the input power is basically
dissipated into its equivalent circuit and the load with Yn =
Gn + jBn, where Yn, Gn, and Bn represent admittance,
conductance, and susceptance, respectively [4] [6].
Resonant conductance would play important part of the
design of waveguide array antenna. Considering each slot
excitation, the synthesis continues by evaluation of required
admittance. The nth slot normalized resonant conductance gn.
The nth slot normalized resonant conductance gn, can be
written as (2) 2
2
1
nn N
i
i
ag
a
1,2,...,n N (2)
TABLE I
Antenna Parameters Summary
Other slot parameters such as depth of the slot d and the
inclined angle θ of each individual slot must be selected so
that the desired electric field distribution generated in the
linear array would match the Taylor aperture field
distribution. Those specified parameters d and θ were then
simulated using EM software tools. In the resonant condition,
the admittance of the aperture is a real number, while the
susceptance as imaginary part is zero. Thus, we assume
quadratic relation with the form d and θ = Xgn2+Ygn+Z. The
coefficients X, Y, and Z were determined by least squared
method by fitting quadratic polynomial to the data of
simulation. Table 1 summarizes final parameters of the
antenna.
4. Analysis and Simulated Results
The simulated results show good radiation pattern and
excellent performance. The radiation pattern of the
constructed two hundred slots gives a horizontal half-power
beamwidth of 0.4° and a vertical half power beamwidth of
18.5°. The bandwidths for the antenna is 8.6% for 200-
elements (8.67GHz-9.45GHz) with VSWR of 1.5. Fig. 3
shows the antenna gain and cross polarization level of the
full-array antenna at the desired frequency. The antenna’s
maximum gain at the main lobe is 36.7 dBi at 9.4 GHz (200-
elements), and 36.6 dBi at 9.35 GHz (200-elements)
respectively.
The Front to back ratio are 59.84dB at 9.4 GHz, and
61.09dB at 9.35 GHz, respectively. When the θ=0°, the
cross-polarization level is suppressed below -28 dB in all
angles of ϕ. The width of the radiating slots is the key
parameter of the cross-polarization. However, it also affects
the bandwidth.
5. Conclusion
The antenna radiation characteristics of the slotted
waveguide array antennas with the feature of low SLL and
low beamwidth are designed and simulated. The antenna is
designed for X-band at 9.4 GHz. V-shaped metal reflector
was included as design innovation to improve the antenna
gain and to achieve antenna beamwidth requirement. The
bandwidths at 9.4 GHz are approximately 780 MHz. At the
desired frequency, 36.7 dBi gain with more than 80%
antenna efficiency for full array antenna (200 elements) are
achieved.
References
[1] R. K. Enjiu, M. B. Perotoni, “Slotted Waveguide Antenna Design
Using 3D EM Simulation,” Microwave Journal., July 2013. [2] E. T. Rahardjo, D. P. Yusuf, Basari, F. Y. Zulkifli, “Microstrip Array
Antenna for X-band Radar Application,” Proc. APMC 2015, Nanjing,
China, 2015 [3] Moh. Amanta K. S. Lubis, D. P. Yusuf, C. Apriono, and E. T.
Rahardjo, “The Effect of Flange Connectors on The Radiation Performance of Narrow Wall Slotted Waveguide Antenna at X-Band
Frequency,” Proc. ISAP 2017, Phuket, Thailand, 2017.
[4] Gilbert, R. A., “Waveguide slot antenna arrays," Antenna Engineering Handbook, 4th Edition, J. L. Volakis, Ed., McGraw-Hill,
2007. [5] IALA Recommendation V-128 On Operational and Technical
Performance Requirements for VTS Equipment, Association of
Internationale de Signalisation Maritime Edition 3.0., Jun. 2007. [6] Jasik, H. and R. C. Johnson (1984). Antenna Engineering Handbook.
Second Edition. McGraw-Hill, New York.
n an gn θ (o) d (mm)
1 0.03 0.000023 6.157 2.521
2 0.03 0.000023 6.157 2.521
3 0.03 0.000023 6.157 2.521
4 0.04 0.000042 6.16 2.521
5 0.04 0.000042 6.16 2.521
… … … … …
200 0.03 0.000023 6.157 2.521
Fig. 3. Radiation Characteristics of the Slotted Waveguide Antenna with V-shaped reflector
2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea
266