[ieee 2011 ieee international conference on control system, computing and engineering (iccsce) -...

2.46 GHz Reduce Size Helical Antenna Simulation Samihah Abdullah

Dayang Suhaida Awang Damit Belinda Chong Chiew Meng

Rohaiza Baharuddin Faculty of Electrical Engineering ,

Universiti Teknologi MARA MALAYSIA, 13500 Permatang Pauh, Pulau Pinang, MALAYSIA

[email protected] [email protected]

Abstract— This paper is to focus on to design of the basic geometry of helical antenna in small size at frequency 2.46 GHz. Several parameters dimensions and helical profiles were studied in order to obtain a suitable frequency range. The software that was applied for this simulation is the CST Microwave Studio (CST MWS) which is analytical tool that provides an accurate 3D EM simulation results for high frequency designs. From the simulation designs, the return losses were obtained. There were less than -8 dB. The results conclude that the helical antenna performed the properties of the 2.46GHz frequency range. From the simulation, the results obtained were S parameter, farfield, bandwidth and gain of the antenna. In a nutshell, all the simulation results of revealed that the designed helical antenna performed at 2.46GHz (Ultra High Frequency (UHF). At this 2.46 GHz can be applied to serve for a number of wireless applications including for WiMAX (Worldwide Interoperability for microwave Access) technologies.

Keywords- Antenna; Helical; UHF system; Communication

I. INTRODUCTION The growing demand for wireless services has made the high requirement for best possible performance from antenna. Because all wireless communications are dependent on antennas, helix antenna or helical antenna have long been popular in applications from VHF to microwaves requiring circular polarization, since they have the unique property of naturally providing circularly polarized radiation. Moreover, its high-gain direction antenna that can increase the range at which wireless devices can receive a signal. A helical antenna works well for trying to acquire a wireless signal at a distance. The helical antenna, consisting of wire wound around cylinder and feed by a coaxial cable, was first introduced by Professor Kraus (Kraus, 1988). In most cases, helical antennas are mounted over a ground plane. Helical antennas can operate in one of two principal modes: normal (broadside) mode or axial (or end-fire) mode. The Helical antenna is a simple way of obtaining high-gain and a broad band of frequency characteristics. This special characteristic of helical antenna makes it popular among other type of antenna.

Radiating at 90 degrees from the axis of the helix is efficient as a practical reduced-length radiator when compared with the operation of other types such as base-loaded, top-

loaded or center-loaded whips. They are typically used for applications where reduced size is a critical operational factor. These simple and practical shapes were primarily designed to replace very large antennas. Usually, their reduced size is therefore most suitable for Mobile and Portable High-frequency (HF) communications in the 1 MHz to 30 MHz operating range.

In previous studies [1], the emphasis has been put on the art of engineering to minimize and optimize these compromises to provide a solution that meets the requirements of each specific application. Most antennas operate in the size regime where their physical dimensions are on the order of the wavelength of operation. Much theoretical work over the years, as well empirical results, indicate that antenna size reduction results in compromises of some key performance characteristics, most notably efficiency and bandwidth. In this paper, the small size of 2.46 GHz antenna was introduce to fulfill the growing demand for high system capability, high transmission rate, and fourth generation.

In order to design and simulate the helical antenna in 2.46GHz, CST MICROWAVE STUDIO (CST MWS) will be used. CST MWS enables the fast and accurate analysis of high frequency (HF) devices included an antenna and multi-layer structures, SI and also EMC effects. The antenna itself is modelled as a planar structure.

While the initial investigation of helical antenna was very revealing, a more in-depth study of this antenna is required in order to understand the effects of the antenna parameters on the radiation characteristics. This indentified improved designs that provide better electrical performance (e.g., higher gain, lower axial ratio, etc,) and/or require smaller antenna size.

II. NORMAL-MODE HELICAL ANTENNA For helical antenna, it has widely application especially for

daily use. Monopole normal mode antennas (NHA) are widely used for business portable radios. Unlike cellular phones, the radio body of the business portable radio is commonly attached to the belt of the user so that the use of the radio does not hinder business activities (Koichi Ogawa et al., 2003).

2011 IEEE International Conference on Control System, Computing and Engineering

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Normal-mode helical antennas are frequently used in mobile communications. They have the characteristics of small size and easy to manufacture. They are frequent substitutes for monopole antennas, which are larger in size. Adaptive antenna arrays have been frequently proposed for used in mobile communications systems especially at the base stations. The helical antenna array is shown to have a better performance than an equivalent monopole antenna array in the presence of mutual coupling effect.

Antennas with circular polarization radiation have found wide applications in mobile satellite communications and direct satellite broad-casting systems due to their insensitivity to the ionospheric polarization rotation [3,8].

A quadrifilar helix antenna can produce circular polarization radiation over the whole upper half space but it exhibits narrow-bandwidth and requires a complicated feeding method [2]. A spherical helical antenna can produce a circular polarization radiation over a wide angular region but it is difficult to maintain a stable vertical position over the ground plane [7].

The hemispherical antenna, unlike the spherical antenna, is not only smaller in size but also provides more robust and low profile structure. It can produce circular polarization radiation over a wide angular range with a relatively high gain [3,8]. These new helical antenna characteristics have a potential application in communication systems in the Ultra High Frequency (UHF) examples are mobile satellite communication, radar, wireless communication, and audio as a broadband applications and WiFi application.

III. SIMULATION

For the simulation parameter was obtained after the design and optimization in CST MICROWAVE STUDIO. With the calculation parameters as a main reference, the geometry of helix is designed in order to obtain the simple and small size of helix. With the simulation process, the basic geometry of the helical antenna as details below:

Diameter of helix, D = 45.01mm Spacing, S = 32.65mm Number of turns, N where (setting in CST, N = 12.5) Circumference, 141.40mm

Total length, no of turns x spacing For the above measurement as basic parameters defined in

order to build the structure of helical antenna. The diameter of wire is 500 mm ; also consider negligible effect to the performance to the antenna. With the fix of diameter of helix, of 45.01mm and the separation, S of 32.65mm, the helical antenna was build and thus optimized by the number of turn of 12.5. The result of simulation was taken and investigates.

IV. RESULT

The simulation results such as S11 parameter, far field pattern, polarization, gain and bandwidth are investigated for the design of helical antenna. The design were not only in 2.46GHz but also the design must be simple, easy to construct and in small size.

The design must be in the range of Ultra High Frequency (UHF) 0.3 GHz to 3 GHz. With the fix of bottom feeding position and the ground plate each design was simulated and the result was investigated. The designed geometry of basic helical antenna can be shown as Figure 1.

Figure 1: Basic geometry design of helical antenna in CST.

The simulation result of S11 response is as in Figure 2.

From the simulation results of S11 parameter, the frequency response was obtained at 2.4762 GHz.

Figure 2: Simulation result of basic helical antenna

At the bottom feeding where the port was placed, there was an electromagnetic flow to the helical antenna for E-Field and for H-Field.

In depth investigation of the simulation results such as far field polar, far field pattern and the bandwidth are presented at design of helical antenna. There is a value of diameter, distance, lap number, the ratio of the radius and total length for the design of helical antenna will be shown on the next part.

A. Design of Helical Antenna (Basic geometry design)

The design was based on the basic geometry design of helical antenna. The result simulation investigated. For the


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design, the basic parameter of helical antenna is as details below:

• Diameter of helix, D = 45.01 mm

• Spacing, S = (Antenna Height – Height of the feeding) / Number of Turns

= ( A – H ) / N = (410.5 mm – 5.656 mm) / 12.5 = 32.65 mm

• Number of turns, N= 12.5

• Circumference, C = πD = 141.4 mm

• Total length, ℓ = Number of turns X Spacing

= N x S = 12.5 × 32.65 mm = 404.86 mm

For the geometry design as Figure 3, the total length is 326.3 mm. The radius ratio is 1.

Figure 3: The Geometry Design

B. S-parameter

Figure 3.6 shows the S-parameter simulation results of S11 for one port of feeding. In practical, it is impossible to get the infinite log magnitude for the reflected signal since there will be losses whether due to the conductor loss or surface loss. Hence, the task is to minimize the losses by matching load impedance to the characteristic impedance which is 50Ω. From the results, the return loss was -8.4103146 dB at the frequency 2.4762 GHz.

Figure 4: S11 parameter

C. Bandwidth

Figure 5 shows the bandwidth parameter of 8-dB bandwidth was 0.0225 GHz (2.4874 GHz - 2.4649 GHz). From the S-parameter result, it can be concluded that the return loss was below -8 dB, which showed that the matching of load impedance to the characteristic impedance.

Figure 5: Bandwidth parameter

D. Radiation Pattern

Radiation pattern is the graphical presentation of 3-dimensional plane which represent its field pattern, side and back lobe, beam width and others antenna parameter. Typically, radiation of two-perpendicular planes was plotted in azimuth or elevation planes. This will give the idea on the performance of helical antenna. The Figure 6 showed the CST radiation pattern in elevation and azimuth plane simulation results at frequency 2.4762 GHz. For elevation plane, the result is shown in the half plane only. This is due to the ground plane of the antenna acts as reflector which reflects all the fields above. Hence, there was no radiation at the lower part of the antenna. In order to measure elevation plane, phi was fixed at φ = 90° and theta was varied. The main lobe magnitude is 14.3 dB with the direction of 90°. The angular width at 3 dB was 31.2°.


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Figure 6: Elevation and azimuth plane for the design

E. Directivity

Figure 7 shows the 3-D view of directivity for the helical antenna at resonance frequency, 2.4762 GHz. This result indicates that this type of antenna produce high directivity averaged at 14.31 dBi. With this characteristic of circular polarization, the far field directivity pattern was in round shape or circularly polarized.

Figure 7: Directivity for the design

Summary of Geometry

Table 3.1: Summary of geometry

Parameter Simulation value

Unit

Diameter, D 45.01 mm

Spacing,S 32.65 mm

Number of turns, N

12.5 None

Circumference, C

141.4 mm

Total length, ℓ

404.86 mm

Pitch angle, θ 13° Degree

Table 3.2: Summary of result simulation

Operating Frequency (GHz)

2.4762 GHz

S11 (dB) -8.4103146 dB

Bandwidth (GHz) 0.0225 GHz

Polarization Circular Polarization

V. CONCLUSION Overall this paper was to study, design and simulate using

the CST MICROWAVE STUDIO for 2.46GHz of helical antenna. Then helical antenna was constructed in order to measure the performance experimentally. All of objectives for this project were being achieved as an expected.

This paper were being studies and explore how to design geometry of helical antenna in small size in 2.46GHz frequency by using CST Microwave Studio as a simulation tools. The simple design enables easy construction of Ultra High Frequency (UHF) antennas. Through the analysis, it’s needed to get the parameter fall at 2.46GHz frequency. With the simulation results, their radiation properties such as circular polarization, wide bandwidth, and relatively high gain were studied in its performance. Moreover, the results showed that the polarization are circularly polarized and the return loss of less than -8 dB.


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In constructing the 2.46 GHz helical antenna, there were some materials and methods were used which considered neglect in the measurement. The electric conductor was used as copper wire in constructing the helical antenna as a helix wound and the aluminium plate for a ground plate. All this materials were used to construct the real hardware small size helical antenna.

Overall this project will brought the benefits to the society which is useful for the basic understanding of design helical antenna in the 2.46GHz range. An essential part of any radio wave communication link is an antenna, which facilitates radiation of electrical signals into space when used as a transmitter or detection of radiation of radiated signals when used as a receiver. The antenna of particular interest in this work is that of a helical geometry which is easy to construct and exhibits radiation properties such as farfield, wide bandwidth, and relatively high gain that are highly desirable in many communication applications.

Lastly, this project was finished and done with successfully design at 2.46GHz helical antenna. This project brought an insight into several designs of High Frequency (HF) of helical antenna. This would become a platform for further research on realizing the implementation of basic radiation of helical antenna for future application systems.

REFERENCES

[1] Samihah Abdullah, Juliana Md Sharif, Nurul Huda Ishak, Asmalia Zanal, M. Aswad A. Mushim, Iza Sazanita, “Simulation for High Frequency (HF) Range of Helical Antenna”, 2010 International Conference on Science and Social Research, CSSR 2010,

[2] Samihah Abdullah, Syed Idris Syed Hassan, “Design Small Size of High Frequency (HF) Helical Antenna”, Signal Processing & Its Applications, 2009, CSPA 2009, 5th International Colloquium.

[3] Niow,C.H,; Mouthaan,K.;Coetzee, J.C.;Hui, H.T., “Design of a Small Size dielectric loaded helical Antenna for Satellite Communications”, Microwave Conference, 2009.AMPC 2009, Asia Pacific.

[4] John D. Kraus and Ronald J. Marhefka,. (2002) "Antennas: For All Applications, Third Edition", McGraw-Hill Higher Education

[5] Balanis, C,. (1982) "Antenna Theory, Analysis and Design", John Wiley and Sons

[6] Stutzman, W,. and Thiele, G,. (1998) "Antenna Theory and Design, 2nd. Edition.", John Wiley and Sons

[7] Cardoso, J. C. and Safaai-Jazi, A. (1993). Spherical helical antenna with circular polarization over a broad beam. Electronics Letter, vol. 29. No.4, pp. 325-326,

[8] Hon Tat Hui, Kam Yuen Chan, Edward Yung, K. N. (2003). Compensating for the Mutual Coupling Effect in a Normal- Mode Helical Antenna Array for Adaptive Nulling. IEEE.

[9] Barts R M (1997). The Stub Loaded Helix A Reduced Size Helical Antenna. Master’s Thesis, Virginia Tech.


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