Planar, High-Gain, Substrate-Integrated Cavity Antenna in the Terahertz Frequency Range Truong Khang Nguyen*
Le Khoa Dang
Division of Computational Mathematics and Engineering (CME), Institute for Computational Science (INCOS), Ton Duc Thang University, Ho Chi Minh City, Vietnam Faculty of Electrical & Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam *
[email protected]
Faculty of Electronics and Telecommunications VNU-HCM University of Science, Vietnam
Ikmo Park Department of Electrical and Computer Engineering Ajou University, Suwon, Korea
[email protected]
Abstract—In this paper, we propose a planar and highly directive cavity type of antenna in the terahertz frequency range. The antenna consists of a frequency selective surface (FSS) and an open-ended narrow slotline dipole, which are both lithographically patterned on a high-permittivity galliumarsenide substrate. The FSS in conjunction with the ground plane of the slitline forms a Fabry–Perot resonator and results in significant directivity enhancement. The simulation results show that the substrate volume determines the effective permittivity of the cavity for the resonance operation. The optimized antenna, which has a size of about 3600 μm × 3600 μm × 175 μm, produced a maximum gain of 14.6 dBi, a radiation efficiency of 55%, and side lobe levels of –14.0 dB and –16.4 dB in the two principal planes at a resonance frequency of 317 GHz.
I.
INTRODUCTION
Millimeter-wave and terahertz frequency range have provided an unprecedented opportunity to explore wireless technologies, systems, and applications, and thus have been attracting considerable attention from researchers over the past decade [1, 2]. However, high total loss, including space path loss and atmospheric attenuation, is one of the main obstacles to the realization of a commercial THz source, particularly in the frequency range of 300 GHz. The remedy for this is the development of high-power sources, efficient detectors, highgain antennas, and low-loss interconnects. In addition, requirements for compact, low-profile, and inexpensive THz sources also need due consideration. A Fabry–Perot (FP) cavity-type antenna is widely being used to enhance the directivity of an antenna by only a single feeding point. A planar FP cavity antenna has been exploited by using an antenna printed on one side of a dielectric and backed by a frequency selective surface (FSS) consisting of double periodic arrays of conducting elements or apertures in a conducting sheet [3, 4]. The radiation behavior of these planar FP cavity antennas relies on the excitation of leaky waves inside the cavity; however, one of the main constraints of this type of antenna is the narrow 3-dB gain bandwidth of the farfield radiation pattern. Nevertheless, their advantages, such as compactness with a low profile, mechanical robustness, integration ability, stability of fabrication and installation, as well as less insertion loss, make them a promising source for the THz frequency region.
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Fully substrate-integrated FP cavity antennas designed for microwave and millimeter-wave regimes on low-permittivity substrates have recently been reported [5–8]. In this paper, the design of a highly directive and planar FP cavity antenna on a high-permittivity gallium-arsenide (GaAs) substrate and operating at 317 GHz is presented. A center-fed open-ended slotline is etched on the top side of the substrate and acts as a perfect reflective mirror. An FSS made of a circular hole array is etched on the bottom side of the substrate and acts as a partially reflecting mirror. The antenna is optimized to have a maximum gain and low side lobe levels in far-field radiation patterns. II.
ANTENNA GEOMETRY AND RESULTS
Figure 1 shows the basic configuration of the proposed FP cavity antenna. The substrate used for the cavity is GaAs (εr = 12.9, tanδ = 0.006) with a substrate thickness and width of H = 175 μm and A = 3600 μm, respectively. An open-ended narrow slit (width ws = 20 μm) is printed on the top layer of the substrate. The slit is center fed by a short dipole that has a width and gap of wd = 10 μm and g = 10 μm, respectively. The antenna is excited by a 50-Ω characteristic impedance discrete port placed at this center feed gap in CST Microwave Studio. The FSS with a 9 × 9 array of circular holes is patterned on the bottom side of the GaAs substrate. The circular hole array is a biperiodic array that has a periodicity and hole diameter of P = 332 μm and D = 204 μm, respectively. The metal layer used for both the ground plane of the slit and the FSS has a thickness of 0.35 μm and a conductivity of 1.6 × 107 S/m. Figure 2 shows the simulated boresight gain of the proposed antenna. The beam collimation was significantly enhanced in the presence of the FSS compared with the bare GaAs substrate. At a resonant frequency of 317 GHz, the maximum gain was about 14.6 dBi, the radiation efficiency was approximately 55%, and the side lobe levels in two principal planes (E- and H-planes) were about –14.0 dB and – 16.4 dB, respectively. In addition, the antenna produced a 3-dB gain bandwidth of 1.4%. Additional antenna characteristics will be presented at the time of presentation. In particular, the influence of substrate volume on the effective permittivity of the cavity for the resonance operation will be discussed in detailed.
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III.
CONCLUSIONS
A planar, high-gain, and fully substrate-integrated cavity antenna made of a high-permittivity GaAs substrate and designed at 317 GHz is presented. The antenna produced high gain and radiation efficiency as well as low side lobe levels in far-field radiation patterns at the resonance frequency. The proposed antenna is, therefore, a promising candidate for use as a compact efficient source in the THz frequency region with high-gain and low-profile requirements. (a) ACKNOWLEDGEMENTS This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number ―103.05-2013.75‖. This work was also supported by Information and Communication Technology (ICT) R&D Program of MSIP/IITP [14-911-01-001].
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(b) Fig. 1. Geometry of the proposed antenna: (a) side view and (b) top view.
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[8]
Fig. 2. Simulated boresight gain of the proposed antenna with and without an FSS.
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