# Compact UHF Circularly Polarized Multi-Band Quadrifilar Antenna for CubeSat
## 1 Introduction
However, this antenna requires a large clearance area, so mounting it on satellites will be pretty tricky. To solve this problem, by analyzing the characteristic mode of the satellite structure, the paper [29] presents a no-need-to deploy antenna that operates at 433 MHz within a 1U dimension. However, the bandwidth is quite narrow, about 3 MHz, which could limit the application of this antenna. In addition, the linear polarization properties and the directional radiation pattern could reduce the quality of the channel and the communication distance. In [30], a proposal based on a meandered folded-shorted patch array is reported. By using a complex coupler network, the input signal could be divided into four paths with the same amplitude. Furthermore, due to the phase shift of 90\({}^{\circ}\) between each port, a circular polarization feature is achieved. However, because of the narrow impedance bandwidth, the high-cost substrate material, and fragile antenna structure, this proposal could not be suitable for satellite application. Designing the antenna with a compact size to be compatible with CubeSat integration and operation at low frequencies with specific properties in polarization and pattern is a considerable challenge. In [31], two frequency reconfigurable antenna structures have been proposed. This system consists of a directional CP antenna based on the quadrifilar helix form and a directional LP antenna based on the Yagi-Uda structure. These antennas support the tunable frequency scheme to extend the effective bandwidth thanks to a gearing system. Recently, several miniature circularly polarized antennas based on a multi-element approach have been proposed to combine a compact form factor with a wide-beamwidth circular polarization [32; 33; 34]. Lacuna Space is a satellite IoT network provider founded in 2017 [35]. Lacuna Space offers a low Earth orbit satellite network using sub-GHz unlicensed bands. The network is natively compatible with the terrestrial LoRaWan network using the same frequency bands. Terrestrial terminals need to know the Lacuna Space constellation almanac in order to wake up at the right time to transmit to the CubeSat. The constellation almanac contains the Keplerian element of each CubeSat orbit, which enables the exact position of any CubeSat to be computed for a given time. Due to atmospheric drag, and moon and sun influence, the almanac is valid for up to one month; then, it needs to be updated regularly. The CubeSatdescribed in this paper aims to broadcast from space the almanac information on the Lacuna Space constellation in the 870 MHz and 920 MHz bands to terrestrial nodes. Circular polarization is required to avoid misalignment between the transmitter and receiver and to reduce the Faraday effect. Additionally, the volume available for the antenna system is extremely limited as the antenna is positioned on the 1U face. Considering the mechanical frame structure and depending on the launching system, the maximal height is 10 mm. A non-deployable solution is chosen to limit any risk linked to the deployment system. This article presents a low-profile, miniature, and multi-band antenna for 3U CubeSat that supports terrestrial ISM bands with right-hand circular polarization. The antenna is designed based on the combination of a broadband power splitter structure and inverted-F antenna elements (IFA) to obtain the directional radiation pattern. In addition, the proposed design provides bandwidth expansion thanks to coupling with a shorted parasitic element. A CubeSat-suitable robust structure is archived using the plastic bumper as the spacing. The antenna is manufactured, mounted on the satellite frame, and then measured in the chamber to validate the concept. Finally, the antenna was integrated within LS3 Lacuna Space CubeSat, launched in September 2020, then commissioned, and used for in-flight experiments in February 2021.