Design of a compact new shaped microstrip patch antenna for satellite application.
Presently, among microwaves and wireless engineers, the demand for miniature antennas on wireless communications have been one of the most pioneering topics in antenna theory and design. Among different kinds of antennas, microstrip patch antennas have attracted much interest due to their lightweight, low profile, easy to fabricate with standard integrated circuit techniques and can be easily incorporated in arrays and with electric components. But microstrip antennas typically suffer from narrow band width and low gain, limited power capacity, poor polarization purity and tolerance problem. Among them, narrow band width and low gain are its main drawbacks [Pozar, D.M., 1992, Shakib, M.N et al. 2010]. Researchers have been proposed and investigated many techniques to overcome these major problem such as slotted patch antennas, microstrip patch antennas on electrically thick substrate, probe feed stack antenna and the use of various feeding and impedance matching techniques and the use of multiple resonators [Islam, M.T et al., 2009; Ramadan et al., 2009; Li, H, et al., 2007; Zhang, L et al., 2008; Azim et al., 2011; Naghshvarian-Jahromi et al., 2009; Naghshvarian-Jahromi et al., 2008, Abbas-Azimi et al., 2007; Li, H et al., 2007; Ren et al., 2007; Elsadek et al. 2007; Liu et al. 2007; Azim et al. 2011]. Through these type of techniques, researchers have found various resonance frequency in different band for fulfill the different types application. For the increasing use of broadband satellite system to provide ever-present and high capacity communications on the move that can be installed unobtrusively on land vehicles and aircrafts, a demand for low profile and lightweight antennas with a small foot print has been mandatory. For satellite communication, antenna technology is a gradually more interesting commercial market for mobile satellite terminals. Different types of application like land application, aeronautical or maritime navigation, and such system must be able to receive satellite broadcasting services with moving. In this study, ku band is considered for automotive tracking applications with the possibility of realizing compact cost effective small antenna [M. Habib et al., 2012].
In [M. Habib et al., 2012] A w shaped microstrip patch antenna is designed with radiating patch dimension 3.5 mm x 5.5 mm and 1.5 mm thickness without ground plane. Although bandwidth is high but gain is low. Another w shaped [M.N. Shakib et al., 2010] patch antenna which dimension 72 mm x 50 mm x 16 mm to achieve good result but size is big which is not suitable for incorporating in satellite. In [Azim. R et al., 2011], dual polarized microstrip patch antenna has designed for ku band application whose result is good but dimension 15 mm x 15 mm and thickness 1.5748mm. For dual polarizing the author used two ports which is not easy for fabrication. In [Islam M.T. et al., 2010], they have proposed a rectangular shaped with complex slot cutting but their average gain is not good. Actually substrates are chosen with higher value of dielectric constant to diminish the size of the antenna [Mobashsher et al. 2012; Shakib, M.N 2010; Bahl et al. 1980; Hammerstad et al. 1975; Balanis, 1989]. Our aim is to shrink the size of the antenna as well as enhance the operating bandwidth. In this paper we have proposed a new micro strip radiating patch shape that achieves high gain compared to others and medium operating frequency for aircraft, space craft and satellite based communication system.
The initial geometry of the proposed patch antenna was first designed implementing the equations from the transmission line model (TEM) approximation in which patch radiating element is viewed as a transmission line resonator with no transverse field variations. In the reported literature [Garg, et al. 1980], the approximation states that the width and length of the patch antenna can be modelled according to the specified central frequency by below equations:
W = [c/2[f.sub.0]] [square root of ([[epsilon]r + 1]/2)] (1)
L = [c/2[f.sub.0][square root of [[epsilon].sub.e]]] - 2[DELTA]l (2)
Where L is the length of the patch, W is the width of the patch, fo is target resonance frequency, c is the speed of light in a vacuum and the effective dielectric constant can be calculated by the equation:
[[epsilon].sub.e] = [[[[epsilon].sub.r] + 1]/2] + [[[[epsilon].sub.r] + 1]/2] [square root of (1 + [10h/W])] (3)
Where, and h is the thickness of the substrate and er is the dielectric constant of the substrate. Because of the fringing field around the periphery of the patch, electrically the antenna looks larger than its physical dimensions. [[DELTA].sub.1] takes this effect in account and can be expressed as:
[DELTA]l = 0.412h [([[epsilon].sub.r] + 0.3)([W/h] + 0.264)]/([[epsilon].sub.r] + 0.3)([W/h] + 0.8)] (4)
As the antenna is fed with the probe feed, the length of the probe feed is also calculated. The input impedance of the antenna must be matched to the probe feed line by choosing the correct position for the feeding point.
After taking account the design requirements such as bandwidth and dielectric constant, the antenna is initially designed to operate in dual frequency at Ku-band and consequently optimized to obtain the most preferable size of the patch using Ansoft's 3D full wave electromagnetic simulator HFSS.
The geometry of the proposed patch slotted antenna is shown in figure 1. It is printed on Rogers RT/duroid 6010 substrate of thickness (h) =1.905 and relative permittivity, [[epsilon].sub.r] = 10.2, loss tangent tan[delta] = 0.0023. A rectangular slot is cut on the ground plane. A 50 ohm coaxial probe feeds a microstrip line, etched on the left side of the radiating patched with dimension of Lf and Wf. The antenna has a compact structure and total dimension is 9.50 mm by 7.96 mm by 1.905mm. Actually the radiating patch is a rectangular structure with three triangular slots. The area and the position of these three triangular slots are responsible for varying resonance frequency. Each triangular slot has two arms equal and third arm's length is twice than others. Length of each triangular arm Lt = 4mm and width Wt = 2.82mm. Because of these three triangular slots, current lines are changed. The current has to flow around the patch. So the effective length of the current lines becomes longer and the antenna size has miniatures. In order to achieve good impedance matching and symmetrical excitement, of the middle proposed shaped antenna, the feeding of the antenna is selected to be symmetrical along the line centred at the midpoint of y axis length of the antenna.
[FIGURE 1 OMITTED]
Result and Discussion
The different characteristics of the proposed shape antenna is investigated and optimized by commercially available finite element based software HFSS 13.0.2. The reflection coefficient results are shown in Fig 2.
[FIGURE 2 OMITTED]
In that figure, the operating frequency is 445MHz from 15.27GHz to 15.72 GHz, where VSWR [less than or equal to] 2 is. The resonance frequency of that region is 15.48GHz where maximum return loss -39.84dB.
As shown in fig.3, the average peak gain of the proposed antenna is almost 6 dBi, the gain variation across the operating band is only .05dBi. The gain is almost higher than compared to other antenna design.
[FIGURE 3 OMITTED]
The radiation pattern for E plane and H-plane of the proposed antenna at cut off frequency depicts in fig 4 (a) and (b). The co -polarization is symmetric and omnidirectional. Broad Beam width is observed in the main beam of co-polarization (E-plane). From the radiation pattern, it can be easily says that the designed antenna produces omnidirectional radiation and almost stable radiation pattern throughout the whole operating band with low cross polarization. The 3D radiation pattern of the proposed shaped is shown in Figure 5.
[FIGURE 4 OMITTED]
Figure 6 depicts the current distribution on the patch at resonance frequency 15.48GHz. The direction of current is indicated by Arrow sign. It is clearly observed from the current distribution display that the electric current strongly flows at the edge of the triangular slot, especially near the feeding probes of the patch. So, we can say that the slots dominate the antenna performance. Due to the triangular slot, the current flow is controlled which leads the lessening of cross polarization level. At different part of the patch, the current distribution is almost regular.
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
In this paper, a single feed, single slayer compact triple equalitarian triangular slot microstrip antenna has been proposed. It is shown that proposed shaped antenna can operate in Ku band. Triple equalitarian triangular slot reduced the size of the antenna and increase the bandwidth. An optimization between size reduction, bandwidth enhancement and high gain also maintained in this work. Since the radiation pattern is omnidirectional, so it is suitable for satellite application.
The author would like to thank the institute of space science (ANGKASA), University Kebangsann Malaysia (UKM) for grant this work.
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M. Samsuzzaman, M.T. Islam, J.S. Mandeep
Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia Selangor, Malaysia.
Corresponding Author: M. Samsuzzaman, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia Selangor, Malaysia
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|Title Annotation:||Original Article|
|Author:||Samsuzzaman, M.; Islam, M.T.; Mandeep, J.S.|
|Publication:||Advances in Natural and Applied Sciences|
|Date:||Apr 1, 2012|
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