Microstrip Antenna Array For CubeSat Application

In this paper, a circularly polarized 2×2 microstrip antenna array was proposed to be utilized in the CubeSat. The array can be mounted on the bottom side or on the side face of the CubeSat to communicate with the earth station or communicate with another Satellite. The proposed antenna array operated in C-band spectrum that extends from 5.9 GHz to 6.4 GHz. The proposed array is consisting of four circularly polarized antenna units (CPAUs) that were arranged in a rectangular configuration. Three T-sections power divider and four sections of quarter wavelength (QWL) microstrip lines were used to connect CPAUs together to obtain a perfect impedance matching. The CPAU is composed of a combination of two orthogonal microstrip square patch antennas with a quadratic phase between them. The proposed array achieves right-hand circular polarization (RHCP) over the operating C-band. The gains for the proposed antenna array are equal 13.14dBi, 13.8dBi, and 10.72dBi at frequencies of 5.9 GHz, 6.15 GHz, and 6.4 GHz, respectively. The total efficiencies vary from 83.2 % to 83.8% over the band of interest. The array was fabricated on Ro4350B with a thickness of 1.524 mm.

I. Introduction

Nowadays, the small satellite technology represents an essential importance among the space transponder due to its small size. A small satellite is a satellite that weighs less than 500 kg [1]. The cube satellite (CubeSat) represents one of the small satellite types that used for communication networks such as sixth – generation communication, space research projects, remote sensing, deep space missions and interplanetary missions [2]-[4]. The CubeSat transponder was conceived for the educational goals at the beginning of the matter. The CubeSat size extends from the smallest existing CubeSat design of 0.25U to the largest one of 27U and the CubeSat mass ranges from 0.2 kg to 40 kg, respectively [1]. The CubeSat with size of 1U represents a dimension of 10×10×10 cm³. CubeSats are commonly operated at the low earth orbit (LEO) and the geostationary earth orbit (GEO). The antenna of the CubeSat is the important part in the communication link. Since the CubeSat has both a small size and lightweight, the microstrip technology was selected in order to achieve the aforementioned limitations based on its pros. The advantages of the microstrip technology are low fabrication cost, small size in height, support both linear polarization as well as circular polarization and the antenna can be integrated with the radio frequency (RF) transceiver circuits. There are many challenges for the antennas that are used in the CubeSat subsystem such as high gain, wide bandwidth, circular polarization, small size, and low mass. Many operating spectrums are allocated to setup the CubeSat’s communication link such as, C-band, S-band, VHF-band, and Ka-band. The circular polarization represents one of the most important antenna parameters for the CubeSat. The circular polarized antennas are immune from the multipath effect, and the Faraday effect at the ionosphere layer than the linear polarized one [5]. C-band microstrip antenna designs are printed in [6]-[7]. In [6], the antenna module was designed to be used for the inter-CubeSat communication link. The antenna module composed of four 1×2 antenna arrays located on the four faces of the CubeSat. Each antenna array consists of two perpendicular rectangular transparent patch antennas. The patch is designed from fluorine doped-tin-oxide films (FTO) with dimension of 14mm×14mm×1μm located on a glass substrate with ε_r= 4.5 and loss tangent of 0.01. The dimension of the glass substrate that located underneath the patch is 14mm×14mm×1mm. The two patch antennas were excited by two 100-ohm feeding lines with proximity feeding technique and connected together with a 50-ohm feed line. The feeding circuit located on a glass substrate with ε_r= 4.5 and loss tangent of 0.01. The size of the glass substrate layer that located underneath the feeding network is 83mm×69mm× 1mm. The reason behind using the glass substrate is to enable the sunlight to reach the solar cell located behind the antenna. Moreover, a pair of small triangles are truncated at the bottom right side and the upper left side of each patch to achieve the circular polarization. In case of placing antenna array on solar cell, the antenna operated from 4.78 GHz to 5.3 GHz. Moreover, the gain is 5.9 dBi (i.e. in case of placing the antenna on solar cell panel) and is 8 dBi (i.e. in case of no solar cell panel behind the antenna) at the frequency of 5 GHz. In [7], the antenna composed of 2×2 microstrip antenna array (MSA). The element is an inclined rectangular microstrip patch radiator. A 45-degree rotation was applied to each patch antenna to reduce the mutual coupling between the antenna elements. The antenna array was designed on dielectric substrate of RT/duroid 6002 laminates with ε_r= 2.94, substrate height of 1.524 mm and loss tangent of 0.0012. The four patches are excited by using a corporate feeding network circuit. The input 50-ohm microstrip feed line is branched into two 100-ohm feeding lines (i.e. T-junction). Each 100-ohm microstrip feed line is matched to 50-ohm microstrip feed line by using a quarter wave transformer section with impedance of 70-ohm. The dimension of the dielectric substrate that located underneath the patches is 74mm×74mm×1.524mm. The MSA array is placed on the sided face of the CubeSat. The antenna operates from 5.71 GHz to 5.89 GHz with bandwidth of 180 MHz. Therefore, the antenna supports to operate in C-band applications such as meteorological radars. The antenna array is dual circular polarization. The realized gain is 13.34 dBi at the center of the operating band.