2018 International Symposium on Antennas and Propagation (ISAP 2018) [ThE2-5] October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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 match to side lobe level requirement. Later, two metal sheets characteristics is designed at the 9.4-GHz frequency (X-band) as metal reflector are attached to the SWA edges to focus its for radar application. The antenna design consists of 200 narrow-wall slots with novel design of V-shaped metal reflector azimuth plane beam. The reflection coefficient, radiation to enhance side lobe level (SLL) and gain. New optimized slot pattern plots, and gain results of the antenna are reported. 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. 2. Antenna Configuration Index Terms — slotted waveguide antenna, X-band, narrow- The 3-D view of the proposed antenna configuration is wall slots, high gain, metal reflector, radar 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 1. Introduction with its parameters is shown in Fig. 2. The antenna radiates Radar is essential component used for detecting hazards horizontal polarization and determines the parameters w = (such as coastlines, islands, icebergs, other objects or ships), 1.58 mm and t = 1.25 mm. The antenna also has two and assisting the navigator in making timely decisions. The independent parameters to be optimized: d (depth of the slot) majority of VTS services use X-band radars as a best and θ (slot inclination angle). compromise, especially since technologies for rain clutter In this work, the design criteria are specified to fulfil the suppression have been matured. Also, as a result of IALA V-128 Recommendations for minimum first lobe side production volume, X-band radars are the least expensive. lobe level suppression of 26 dB and 33 dB at 10 degree or Antenna system is used on many platforms such as ships, more outside the main lobe [5]. Those requirements are ports, or surveillance tower need to be high gain with tightly- recommended for Basic level of VTS radar type. Other controlled beamwidths, strong, compact, lightweight and parameters are also specified to be less than 22° for vertical resistant to the effects of roll and motion. [1-3]. Low side half-power beamwidth, less than 0.5° for horizontal half- lobe level and high efficiencies antenna performance are also power beamwidth, cross-polarization < -25 dB, and front-to- required to fulfil the VTS equipment standards. Slotted back ratio >30 dB. Similarly, 200 number of slots and waveguide antennas can fulfil all of these criteria. Slotted optimal slot spacing of 0.7λ are employed to achieve the waveguide antennas (SWAs) [4] radiate energy through slots requirements of -30 dB SLL and horizontal half-power cut in conducting broad or narrow wall of a rectangular beamwidth < 0.5°. V-shaped metal reflector is employed and waveguide. These slots introduce discontinuities in the proposed as the design innovation in order to enhance the conductor and interrupt the current flows along the antenna gain and achieve desired beamwidth for radiation waveguide [1]. SWAs can be realized as resonant or non- pattern. resonant according to the wave propagation inside the By using (1): waveguide (respectively standing or traveling wave). 180 (1) Gain Gainsingle+3log 2 n 3log2   dB  In this paper, a slotted waveguide antenna is designed for  operation at X-band frequency (8 to 10 GHz). Its scanning Where Gainsingle is the gain of a single slot. In this paper, beam requires a narrow beamwidth in the azimuth plane and gain of single antenna slot (Gainsingle) ~ 5dB, n = 200, 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

Fig. 1. Full 3D view of X-band slotted waveguide antenna Fig. 2. Antenna dimension with its parameters with V-shaped metal reflector configuration

265 2018 International Symposium on Antennas and Propagation (ISAP 2018) October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea with ϕ = 30° results in gain of 35.7 dB which is satisfied to 4. Analysis and Simulated Results meet the Basic level of specifications for marine radar. The simulated results show good radiation pattern and excellent performance. The radiation pattern of the 3. Antenna Synthesis constructed two hundred slots gives a horizontal half-power A finite percentage of the input power is basically beamwidth of 0.4° and a vertical half power beamwidth of 18.5°. The bandwidths for the antenna is 8.6% for 200- dissipated into its equivalent circuit and the load with Yn = elements (8.67GHz-9.45GHz) with VSWR of 1.5. Fig. 3 Gn + jBn, where Yn, Gn, and Bn represent admittance, conductance, and susceptance, respectively [4] [6]. shows the antenna gain and cross polarization level of the Resonant conductance would play important part of the full-array antenna at the desired frequency. The antenna’s design of waveguide array antenna. Considering each slot maximum gain at the main lobe is 36.7 dBi at 9.4 GHz (200- excitation, the synthesis continues by evaluation of required elements), and 36.6 dBi at 9.35 GHz (200-elements) th respectively. admittance. The n slot normalized resonant conductance gn. th The Front to back ratio are 59.84dB at 9.4 GHz, and The n slot normalized resonant conductance gn, can be written as (2) 61.09dB at 9.35 GHz, respectively. When the θ=0°, the cross-polarization level is suppressed below -28 dB in all a 2 n nN 1,2 ,. . . , (2) angles of ϕ. The width of the radiating slots is the key gn  N 2 parameter of the cross-polarization. However, it also affects ai i1 the bandwidth.

TABLE I 5. Conclusion Antenna Parameters Summary The antenna radiation characteristics of the slotted o n an gn θ ( ) d (mm) waveguide array antennas with the feature of low SLL and low beamwidth are designed and simulated. The antenna is 1 0.03 0.000023 6.157 2.521 designed for X-band at 9.4 GHz. V-shaped metal reflector 2 0.03 0.000023 6.157 2.521 was included as design innovation to improve the antenna 3 0.03 0.000023 6.157 2.521 gain and to achieve antenna beamwidth requirement. The bandwidths at 9.4 GHz are approximately 780 MHz. At the 4 0.04 0.000042 6.16 2.521 desired frequency, 36.7 dBi gain with more than 80% 5 0.04 0.000042 6.16 2.521 antenna efficiency for full array antenna (200 elements) are achieved. … … … … … 200 0.03 0.000023 6.157 2.521 References

Other slot parameters such as depth of the slot d and the [1] R. K. Enjiu, M. B. Perotoni, “Slotted Waveguide Antenna Design Using 3D EM Simulation,” Microwave Journal., July 2013. inclined angle θ of each individual slot must be selected so [2] E. T. Rahardjo, D. P. Yusuf, Basari, F. Y. Zulkifli, “Microstrip Array that the desired electric field distribution generated in the Antenna for X-band Radar Application,” Proc. APMC 2015, Nanjing, linear array would match the Taylor aperture field China, 2015 [3] Moh. Amanta K. S. Lubis, D. P. Yusuf, C. Apriono, and E. T. distribution. Those specified parameters d and θ were then Rahardjo, “The Effect of Flange Connectors on The Radiation simulated using EM software tools. In the resonant condition, Performance of Narrow Wall Slotted Waveguide Antenna at X-Band the admittance of the aperture is a real number, while the Frequency,” Proc. ISAP 2017, Phuket, Thailand, 2017. [4] Gilbert, R. A., “Waveguide slot antenna arrays," Antenna susceptance as imaginary part is zero. Thus, we assume Engineering Handbook, 4th Edition, J. L. Volakis, Ed., McGraw-Hill, 2 quadratic relation with the form d and θ = Xgn +Ygn+Z. The 2007. coefficients X, Y, and Z were determined by least squared [5] IALA Recommendation V-128 On Operational and Technical method by fitting quadratic polynomial to the data of Performance Requirements for VTS Equipment, Association of Internationale de Signalisation Maritime Edition 3.0., Jun. 2007. simulation. Table 1 summarizes final parameters of the [6] Jasik, H. and R. C. Johnson (1984). Antenna Engineering Handbook. antenna. Second Edition. McGraw-Hill, New York.

Fig. 3. Radiation Characteristics of the Slotted Waveguide Antenna with V-shaped reflector

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