# Low-Profile Antenna System for Cognitive Radio in IoST CubeSat Applications
###### Abstract  
Since the CubeSats have become inherently used for the Internet of space things (IoST) applications, the limited spectral band at the ultra-high frequency (UHF) and very high frequency should be efficiently utilized to be sufficient for different applications of CubeSats. Therefore, cognitive radio (CR) has been used as an enabling technology for efficient, dynamic, and flexible spectrum utilization. So, this paper proposes a low-profile antenna for cognitive radio in IoST CubeSat applications at the UHF band. The proposed antenna comprises a circularly polarized wideband (WB) semi-hexagonal slot and two narrowband (NB) frequency reconfigurable loop slots integrated into a single-layer substrate. The semi-hexagonal-shaped slot antenna is excited by two orthogonal \(+/-45^{\circ}\) tapered feed lines and loaded by a capacitor in order to achieve left/right-handed circular polarization in wide bandwidth from 0.57 GHz to 0.95 GHz. In addition, two NB frequency reconfigurable slot loop-based antennas are tuned over a wide frequency band from 0.6 GHz to 1.05 GHz. The antenna tuning is achieved based on a varactor diode integrated into the slot loop antenna. The two NB antennas are designed as meander loops to miniaturize the physical length and point in different directions to achieve pattern diversity. The antenna design is fabricated on FR-4 substrate, and measured results have verified the simulated results. CubeSats; reconfigurable antenna; cognitive radio; internet of space things; UHF band 20232347823104782  
a class of intelligent transceivers with increased situational awareness due to their cognitive skills. This can result in the improvement of the efficient and robust use of communication resources and low delay of data exchange in the CubeSat constellation [5; 9; 12; 13] (see Figure 1). While to solve the problems of globality services, the IoST, a pervasive cyber-physical system that will enable full global communication, is recommended (see the IoST services in Figure 1). The use of CubeSat does not limit to previous applications. Still, it extends to serve low data rate links for telecommand, telemetry, and control data for 5G networks at very high frequency and ultra-high frequency (VHF/UHF) [14; 15; 16]. Due to space restrictions, achieving multifunctional antennas in the CubeSat is challenging. Indeed, the antenna is the main key for the CubeSat to provide those aforementioned services (CR and IoST); so, a wideband antenna for sensing and a reconfigurable narrowband antenna for communication in low profile and compact size is mandatory. Thus, some physically changing antenna techniques such as origami folding, hinges, soft robotics, spring forces, and telescopic actuation are implemented [17; 18; 19; 20; 21; 22; 23], but those methods significantly increase the mechanical complexity of the CubeSat. Extensive work has been undertaken to provide antennas for cognitive radio applications [24; 25; 26; 27; 28; 29; 30; 31; 32; 33], but most of them do not fit with CubeSat regarding operating frequency, size, and compatibility. Although several designs have been employed for the CubeSat [34], such as slot antennas [8; 35], the spiral antenna [36], helix [37], aperture antennas [38; 39], superstrate antenna [40], solar cell-integrated antennas [41; 42; 43], dipole antenna [44], and folded dipole antenna [45], they do not support the UHF band with compact size and simple structure. In this paper, a simple structure-folded slot antenna design has been presented. The proposed antenna consists of three antennas; one works as wideband antenna which is fed by two feedlines to provide circular polarization, while the other two are narrowband antennas that are fed by separate feedlines in a different orientation, to achieve radiation diversity. In addition, each NB antenna has a varactor diode. The NB antennas change their frequency over the operating band of the wideband antenna. By changing the value of  
Figure 1: The conceptual scenario of satellite services.