Low Side Lobe Omnidirectional Cylindrical Conformal X-Bnad Microstrip Antenna Design Mohammad-Reza Nickpay Tehran Regional Electric Co

Low Side Lobe Omnidirectional Cylindrical Conformal
X-Bnad Microstrip Antenna Design
Mohammad-Reza Nickpay
Tehran Regional Electric Co.

[email protected]
Abstract—An X-Band cylindrical conformal low side lobe level omnidirectional array is designed in this paper. The radius of the cylinder is 30 mm. The Dolph-Chebychev distribution method has been applied to design seven elements subarray to lower the side lobes. The designed antenna array is composed by circular array of 16 subarrays to cylindrical shape to obtain smooth radiation pattern. The simulation results show that the first side lobe level is -21.8 dB, antenna gain is 10dB, and the relative bandwidth is 2%.

Keywords-component; conformal microstrip antenna; cylindrical microstrip array antenna; omnidirectional; low side lobe level, X-Bnad.

Introduction
Microstrip antenna has many advantages, such as small size, light weight, low profile, and so that is comfortable to planar and nonplanar surfaces. The cylindrical geometry is a sample of nonplanar surfaces which can offer desirable antenna characteristics that is not provided by planar antenna. The microstrip conformal antenna is widely used in satellite communications, radar, weapons and missile telemetry 1-4. A conformal antenna is designed to adopt some prescribed shape, example is a flat curving antenna which is mounted on or embedded on a curved surface. The shape can be a part of aircraft, missiles, and other high speed vehicle.

The communication and telemetry system of aircraft such as Unmanned Aerial Vehicle (UAV) require antenna which have high gain, omnidirectional and light weight. Omnidirectional and 360° coverage needs in the roll of the UAV. Full coverage in the roll plane of the UAV is obtained by using circular array configuration of antenna, according to this view it is studied by many research groups. A type of multi-layer microstrip array antenna presented in 5 can radiate a 360° omnidirectional pattern, and can reach high gain more than 9 dBi of peak gain. Another microstrip antenna for use in UAV was presented in 6. A 32 GHz cylindrical conformal omnidirectional millimeter wave antenna array was studied in 7.

In some precise applications, antennas are required to have low side lobes. In this paper, seven elements subarray has been presented. The cylindrical conformal antenna array includes 16 subarrays to obtain completely smooth radiation pattern. The simulation results show this X-Band cylindrical conformal omnidirectional antenna has good performance.

LOW SIDE LOBE ANTENNA ARRAY
First, The series-fed taper antenna array shown in Fig.1 is the one as in 8, which was used as the starting point of the present work. The array mounted on the top of a grounded dielectric substrate of thickness h = 1.57 mm and a relative dielectric 2.33 constant. With end-fed arrays, the elements nearest the feed couple only a small amount of power and therefore must be fairly narrow. The feed line must be small compared to the narrowest patch. In this case, a 50 ? line will be used. The line width is 0.7 mm that is considerably smaller than the square patch width. The radiating patches themselves are resonant so that the input line to a patch is matched. In the simple transmission line model of a patch, this corresponds to a length of 0.5?g. Because the amplitude and phase of the radiated fields at each patch are determined by the cumulative transmission characteristics of the preceding patches on the line, the transmission characteristics of the patches must be determined accurately in order to achieve a desired amplitude and phase distributions of radiating currents along the array 9.

According to the Dolph-Chebyshev method, power distributions of the elements are shown in Table 1.Values of power amplitude have been calculated for -30 dB side lobe level in theory, so that the maximum value of SLL in reality be -20 dB. The series-fed taper antenna array is designed and shown in Fig. 1. The detailed geometrical parameters are listed in Table 2.

Table 1. The power distributions of seven elements Dolph-Chebyshev array
Element 1 2 3 4 5 6 7
Power Amplitude 0.26 0.56 0.87 1 0.87 0.56 0.26

Fig. 1. Configurations of the single antenna array.

Table 2. Array geometric parameters
Size (mm)

No. i Patch
Width
(W?i) Patch
Length
(L?i) Line
Width
(Wi) Line
Length
(Li)
1 4.17 9.74 0.67 11
2 6.7 9.55 0.67 11
3 8.36 9.41 0.67 11
4 8.98 9.31 0.67 11
5 8.36 9.41 0.67 11
6 6.7 9.55 0.67 11
7 4.17 9.74 0.67 Using CST Microwave Studio, the S-parameters of the series-fed taper antenna array is calculated as depicted in Fig. 2. As illustrated, series-fed taper antenna array shows resonance at 9.7 GHz and a bandwidth of 200 MHz.

The radiation pattern of the antenna array is shown in Fig 3. It shows that maximum gain is 15.5 dB, the first side lobe level is -21.8 dB and half power beamwidth (HPBW) is 11.4? in E-plane. Fig.4 shows that the HPBW is 82? in H-plane.

Fig. 2. Full-wave simulated S-parameters of the series-fed taper antenna array.

Fig. 3. E-plane radiation pattern of series-fed taper antenna array.

Fig. 4. H-plane radiation pattern of series-fed taper antenna array.

CYLINDERICAL CONFORMAL OMNIDIRECTIONAL MICROSTRIP ANTENNA ARRAY
A circular antenna array must be designed in order to achieve an omnidirectional and high gain pattern to meet the demand of long distance for aerospace communication. Based on the seven elements Dolph-Chebyshev distribution array regarded as subarray, a cylindrical conformal antenna is designed to achieve omnidirectional radiation. Assume that the carrier is a cylinder, and the cylinder radius is 30 mm. In order to get smooth radiation pattern, 16 Dolph-Chebyshev distribution subarrays are united. The configuration of cylindrical conformal antenna array is shown in Fig.5.

Fig. 5. Configuration of the cylindrical conformal antenna array.
The cylindrical structure of Fig. 5 have been modeled through CST Microwave Studio. Cylinder with radius 30 mm have been analyzed. The radiation pattern of the antenna array is shown in Fig. 6, 7. The result in Fig.6 indicates that proposed antenna array produced omnidirectional radiation pattern with gain of 10 dB. In Fig.7 result indicates that the maximum gain difference between Point 1 and Point 2 is 1.42 dB (Point A is 10.05 and Point B is 8.63 dB), showing complete omnidirectional radiation and minimum distortion in radiation pattern.

Fig. 6. The Polar radiation pattern of the omnidirectional antenna array.

Fig. 7. The Cartesian radiation pattern of the omnidirectional antenna array.

Microstrip POWER DIVIDER FEEDING NETWORK
There is one feed point in this omnidirectional antenna array. The power divider feeding network must feed 16 subarrays. The configuration of the 1:16 Wilkinson power divider feeding network is shown in Fig.8. The Wilkinson power divider mounted on the top of a grounded dielectric substrate of thickness h = 0.76 mm and a high relative dielectric 9.9 constant to reduction dimensions of the power divider. The return loss of the feeding network is shown in Fig. 9. The simulation result shows that the impedance matching is proper in frequency band of 9.1 – 10.05 GHz.

Fig 8. The configuration of the 1:16 Wilkinson power divider.

Fig 9. The S11 of the 1:16 Wilkinson power divider.

CONCLUSION
The Dolph-Chebyshev distribution method can lower the side lobes of the microstrip series-fed antenna array. The first side lobe level can reach -21.8 dB, which is much lower than the ordinary series-fed antenna array. The cylindrical conformal omnidirectional antenna array includes 16 subarrays when the cylinder radius is 30 mm. The microstrip Wilkinson power divider feeding network can be used to feed the antenna array. The measurement results show this 9.7 GHz cylindrical conformal omnidirectional antenna has good performance, and the relative bandwidth and the gain of the conformal antenna array are 2% and 10 dB, respectively.

References
V. Jaeck, L. Bernard, Member IEEE, K. Mahdjoubi, R. Sauleau, Senior Member IEEE, S. Collardey, P. Pouliguen, P. Potier : ‘A Conical Patch Antenna Array for Agile Point to-Point Communications in the 5.2-GHz Band,’  IEEE Antennas and Wireless Propagation Letters.

He Zhu, Xianling Liang, Member, IEEE, Sheng Ye, Ronghong Jin, Senior Member, IEEE, Junping Geng, Member, IEEE : ‘A Cylindrically Conformal Array with Enhanced Axial Radiation,’ IEEE Antennas and Wireless Propagation Letters.

Diana Verónica Navarro-Méndez; Hon Ching Moy-Li; Luis Fernando Carrrera-Suárez; Miguel Ferrando-Bataller; Mariano Baquero-Escudero: ‘Antenna arrays for unmanned aerial vehicle,’ 2015 9th European Conference on Antennas and Propagation (EuCAP).

Pattapong Sripho; Suriya Duangsi; Marinda Hongthong : ‘Comparison of antenna for DTI rocket telemetry system,’ 2016 Second Asian Conference on Defence Technology (ACDT).

M. Dogan, and F. Ustuner : ‘A Telemetry Antenna System for Unmanned Air Vehicles,’ Progress In Electromagnetics Research Symposium Proceedings, Cambridge, USA, July 5–8, 2010
Chien-Chun Hung, Yao-Jen Teng, Yung-Sheng Tien, Yu-Tsung Tsai : ‘Development of Low-Profile Antenna for Mini. UAV with Reconnaissance Mission,’ World Academy of Science, Engineering and Technology International Journal of Mechanical, Aerospace, Industrial, Mechatronic and Manufacturing Engineering Vol:6, No:5, 2012.

Jingping Liu; Ning Mu; Fang Lv; Huichang Zhao; Qian Wang; Ying Wang : ‘Low side lobe cylinder conformal omnidirectional millimeter wave microstrip antenna design,’ 2016 46th European Microwave Conference (EuMC).

Sainati,R. A., CAD of Microstrip Antennas for Wireless Applications,Artec h House,Boston,London,1996.

Tao Yuan; Ning Yuan; Le-Wei Li :’ A Novel Series-Fed Taper Antenna Array Design,’ IEEE Antennas and Wireless Propagation Letter.