## 1 Introduction  
The development of nanosatellites or CubeSat provides a unique platform to explore space with a single unit structure of 10 \(\times\) 10 \(\times\) 10 cm\({}^{3}\). Nowadays, numerous nanosatellite missions are launched into space for various applications, such as space education, space tethers, for commercial sectors and for remote sensing like weather forecasting, natural disaster monitoring, maritime tracking, and multispectral Earth imaging. Communication between satellite and earth is crucial for satellite communication, where an antenna plays a key role in the system. The operating frequency of the nanosatellite depends on its requirements and applications, and lower UHF are widely used bands in the nanosatellite communication system [1]. UHF antenna design is a challenging task for antenna researchers due to the inherent relation between antenna size and operating frequency, and nanosatellite standards [2]. Various antenna architectures have been studied and classified under two categories: non-deployable and deployable antennas [3]. Wire antennas, like monopoles and dipoles, are commonly used as the deployable antennas in the nanosatellitecommunication system. Deployment complexity might have a higher chance of satellite mission failure [4]. A 437 MHz half-wave crossed dipole antenna was developed for NUTS CubeSat [5], where element length was considered to be 172 mm. The antennas were made of measuring tape and wrapped around the satellite structure. A nichrome-wire deployment mechanism was utilized for deploying the antennas. To overcome this complexity, non-deployable antennas, like patch antennas, provide an effective solution with better mission reliability. In the last decade, various types of lower UHF patch antennas have been strategically integrated with the nanosatellite structure, designed with good efficiency and impedance bandwidth [5; 6; 7; 8]. [PERSON] et al. developed a UHF patch antenna with high dielectric substrate material, which was designed for a 450 MHz USUSAT nanosatellite communication system [9]. In ref. [10], another printed patch antenna was developed for a UHF 433 MHz communication system, where \(-13\) dB of gain was achieved using 51 \(\times\) 28 mm\({}^{2}\) FR-4 substrate material. In ref. [11], a folded shorted patch antenna was demonstrated for UHF 400 MHz microsatellite applications. The developed antenna offered CP performance with 130 mm \(\times\) 130 mm ground plane. Consequently, [PERSON] et al. developed a multi-layered shorted patch antenna for UHF 400 MHz microsatellite applications [12]. The antenna achieved a gain of 0.4 dBiC with overall antenna dimensions of 150 mm \(\times\) 150 mm \(\times\) 37 mm. Metamaterial patch antennas have been explored for lower UHF nanosatellite communication systems [13; 14]. However, these antennas occupy the surface space of the nanosatellite structure, constraining solar panel placement. Therefore, the conventional UHF patch antenna comes with larger space acquisition, and it becomes very challenging to mount adequate solar panels. The transparent antenna is a potential antenna to overcome the complexity of having sufficient solar cells facing patch antennas, where the antenna is placed above the solar panels and integrated with the nanosatellite structure [15; 16; 17]. In [18], transparent antennas have been developed for ISM band CubeSat applications. However, for lower UHF antenna, the transparent antenna size becomes larger, making the design complex. In this case, the Planar Inverted F Antenna (PIFA) can overcome the problems associated with the antenna and solar panel placement on the limited surface of the nanosatellite structure [19; 20; 21]. In ref. [21], a modified PIFA antenna was developed for the microsat UHF communication system, where the PIFA structure occupied \(85\times 85\times 31\) mm\({}^{3}\) space of the microsat structure. This paper presents a modified PIFA antenna for the 1U nanosatellite communication system.