Spiral Microstrip Antenna

Spiral Microstrip Antenna Dinísio Raony Ribeiro, Leonardo Augusto de Santana, Marlen Carneiro Alves, José Felipe Almeida Amazon Studies Institute (IESAM), Belém, PA, Brazil Carlos Leonidas da S.S. Sobrinho Depto of Elect. and Comp. Eng., Federal University of Pará (UFPA), Belém, PA, Brazil [email protected], [email protected], [email protected], [email protected], [email protected] Abstract — This paper deals with a microstrip antenna that has a spiral geometry rectangular form. This antenna form is based on the analysis of a spiral monopole. Through such configuration, it is possible to obtain a wider bandwidth operation. In addition, a considerable bandwidth in this type of microstrip is verified. Index Terms — Bandwidth, microstrip antenna, spiral antenna.

I. Introduction Several difficulties of a conventional microstrip antenna are related to the narrow operation band [1-3]. Many techniques have been used to solve such problem [4]. This kind of antenna can be integrated with other elements in the circuit that uses planar structures (MMICs - monolithic microwave integrated circuits). In opposition to the microstrip problem, there are the spiral monopole antennas which have radiation patterns and impedance without variation inside of a wideband and, therefore, are known as frequency independent [5-6]. In [7], for example, the authors had used a numerical technique to simulate what they called monopole horizontal spiral, and being on vertical form [9] in relation to the grounding in [8], with the objective to analyze some parameters of these antennas. The purpose of this article is to present a spiral antenna in MMIC configuration, which also can be called rectangular spiral microstrip antenna. All the geometry in this work is based, therefore, in the microstrip antennas [1-3] and in the ideas of analysis made for spiral monopoles [7-8]. So, a model of a simple antenna can be confectioned and the return losses are presented through experimental measurement. II. The model The antenna presented as project of this work is a microstrip. This antenna is fed by a stripline, which will have to compose the entire device in regular orthogonal breakings in spiral form. The substrate was chosen to be 0,7 mm Duroid 5880 and dielectric constant 2.2. The characteristic impedance of the transmission line is 50 Ω. In the following figure (Fig.1) the structure and its geometry are shown.

Fig. 1. Geometry of the spiral microstrip antenna.

III. The FDTD performance This project was firstly simulated to obtain the best performance, and then the antenna was constructed. The FDTD method was implemented by the technique of ABCs UPML [10-12]. The FDTD discretization is made ∆x = 0.3891 mm, ∆y=0.4000mm and ∆z=0.1588mm. So, the feedline is placed in the antenna with the width 6∆x. To maintain the Courant condition, the time discretization was done in such way that ∆t=0.441ps. For the excitation source of the antenna it was considered a Gaussian pulse, whose bandwidth is 3,0 GHz. Therefore, Figs.2, 3 and 4 show the FDTD aspects of the simulated antenna.

Fig.2. FDTD simulation.

Fig.5. Microstrip spiral antenna.

Fig.3. Normalized voltage in the resonant regime by iteration numbers (FDTD).

0 -5 -10

10

120

|S11| (dB)

90 60

0 -10

30

150

-15 -20

Measurements FDTD

-25

-20 -30

-30 -40

Plane x-z Eφ Eθ

180

-30

0

-35 1,00

1,25

1,50

1,75

2,00

2,25

2,50

Frequency (GHz)

-20 -10

330

210

Fig.6. Return loss (measurements and FDTD simulation).

0 10

240

300 270

Fig.4. Electric field radiation pattern (FDTD).

IV. Results Fig.5 presents the circuit of the spiral microstrip antenna. In Fig. 6 is shown a good agreement between FDTD simulation and measured data. Notices that the central resonant frequency is near to 1,69 GHz and, in particular, at -10 dB return loss, the bandwidth (experiment) is close to 23 % (1,5–1,9 GHz).

V. Conclusion The Spiral microstrip antennas are suitable choices for radiating elements because of the relatively wider bandwidth compared to other resonant conventional microstrip. The choice of 1,69 GHz has been done because of the facility to design FDTD simulation, for 50 Ω environment, and due to the available material. But other bands can be used in a more specific project. Moreover, when compared with a monopole, the printed spiral antenna has a good portability and compact structure. The contribution of this study is to present a geometric configuration for the microstrip, which allows operation with wideband without using special techniques.

Acknowledgement The authors wish to acknowledge the assistance and support of the LANE/PPGEE/UFPA and Amazônia Celular. References [1] J. F. Almeida, Análise Fotônica em Estrutura de Microfita Planar Usando o Método FDTD com Processamento Paralelo, UFPa: tese de doutorado, 2004. [2] R. Garg, P. Bhartia, I. Bahl, and A. Ittipiboon, Microstrip Antenna Design Handbook. Norwood: Artech, 2001. [3] E. Chang, S. A. Long, and W. F. Richards, “Experimental Investigation of Electrically Thick Rectangular Microstrip Antennas,” IEEE Trans. Antennas Propagat., vol. 43, pp. 767772, 1986. [4] J. F. Almeida and C. L. S. S. Sobrinho, “Analysis by FDTD Method of a Microstrip Antenna with PBG Considering the Substrate Thickness Variation,” Journal of Microwave and Optoelectronics, vol. 3, no.3, pp.41-48, Dec. 2003. [5] C. A. Balanis, Antenna Theory: Analysis and Design, 2nd ed., New York: John Wiley, 1997.

[6] W. L. Curtis, “Spiral Antennas”, IEEE Trans. on Antennas and Propagat., pp. 298-306, May 1960. [7] J. A. Kaiser, “The Archimedean two-wire Spiral Antenna”, IEEE Trans. on Antennas and Propagat., pp. 312-323, May 1960. [8] K. Q. da Costa, V. A. Dmitriev e C. L. da S. S. Sobrinho, “Análise e Otimização de um Monopólo Espiral Horizontal,” 2 o Momag, Campinas/SP, 2005. [9] K. Q. da Costa, V. Dmitriev, C. Rodrigues, “Fractal Spiral Monopoles: theoretical analysis and bandwidth optimization,” SBMO/IEEE, MTT-S, IMOC, Brasília-DF, Brasil, July 2005. [10] K. S. Yee, “Numerical Solution of Initial Boundary Value Problems Involving Maxwell´s Equations in Isotropic Media,” IEEE Trans. Antennas and Propagat., vol. 14, 302-307, 1966. [11] A. Taflove, Finite Difference Time Domain Methods for electrodynamic Analysis. New York: Artech, 1998. [12] S. D. Gedney, “An Anisotropic Perfectly Matched LayerAbsorbing Medium for the Truncation of FDTD Lattices,” IEEE Trans. Antennas Propagat., vol. 44, pp. 1631-1639, 1996. [13] J. Felipe Almeida, C. L. S. Sobrinho, “Técnica

Computacional para Implementação de Condições de Fronteira Absorvente UPML - por FDTD: Abordagem Completa,” IEEE Revista Latin America Transactions, vol. 3, pp.1-4, 2005.