Design of Narrow -wall Slotted Waveguide Antenna with V … · 2018. 10. 19. · Abstract - Slotted waveguide antenna with wide bandwidth characteristics is designed at the 9.4 -GHz

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]

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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

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