## 3 Antennas with General Aspects Utilized for CubeSat
### Planar Phased Patch Antennas and Their Arrays
A bow-tie antenna was implemented for the S-band, while compact X-band antennas were analyzed for a fixed satellite service (FSS) within \(7.89\)-\(10.49\) GHz, achieving, again, up to \(35\) dB. Another design at \(6\) GHz was categorized in the C-band, while an X-band antenna utilized an SSR background for simulation. Fabrication used chemical etching, and the results were compared in terms of impedance, S11, gain, and directivity. Additionally, the proposed antenna was evaluated as an array element to enhance the gain during transmission and reception [37]. A compact inverted S-shaped patch antenna was designed for three-band operation in the X-band. A fabricated prototype confirmed the design's performance, with measured BWs of \(5.02\%\), \(9.13\%\), and \(3.79\%\) for all bands. Elliptical slots in the ground plane enhanced the gain. The antenna showed strong agreement between simulations and measurements. Its stable gain, omnidirectional radiation, and efficient performance made it suitable for X-band applications [38]. One project focused on designing and implementing a 2 \(\times\) 2 antenna array for X-band radar applications. The compact design operates between 7.5 and 9.8 GHz, achieving a 12.5 dB peak gain with a directional radiation pattern. Stacked patches with an air gap enhance the impedance and bandwidth performance. FR4 and other substrates were initially used for their availability and affordability. Simulations and analyses were conducted using HFSS software [39]. A compact dual-frequency microstrip antenna was designed for S- and X-band operations. Utilizing a 1:3.3 frequency ratio saved space by using the S-band antenna as the ground plane for a 2 \(\times\) 2 X-band array. Electromagnetic coupling enabled measured bandwidths of 13% at the S-band and 6.2% at the X-band (1S11 \(<\) -10 dB), with the isolation exceeding 38 dB. The antenna achieved gains of 7.5 dBi at the S-band and 10.5 dBi at the X-band (Figure 4) [40]. A multi-band, crescent-shaped patch antenna was designed using five nested annular rings. Three rings were merged on the upper section, while two were positioned along the feed line. The key parameters were analyzed, including bandwidth, radiation pattern, gain, impedance, and return loss. The compact design achieved return losses of \(-\)33 dB at 3.1 GHz and 9.3 GHz. Simulated using ANSYS HFSS, the results showed strong agreement with the measurements. The X-band and WLAN bands offered 500 MHz and 4300 MHz bandwidths, making the antenna suitable for various applications (Figure 5) [41]. A rectangular, slot-loaded microstrip antenna with DGS was designed for multi-band operations, achieving high gain across the C-, X-, and Ku-bands. Simulated using HFSS 13.0, the antenna supports frequencies at 6.035 GHz (GNSS), 6.795 GHz (satellite TV), 7.46 GHz (long-distance communication), 8.505 GHz (radar), 11.45 GHz (space communication), 13.35 GHz (detector), 15.06 GHz (military), 17.24 GHz (aerospace), and 19.05 GHz (astronomical observation). Multi-band functionality was enabled by U-slot and rectangular slot cuttings, with no ground or patch modifications required for quad-band resonance. Additional slot adjustments extend operation to nine bands. The optimized slot dimensions enhance the gain, which reached up to 14.679 dB at higher frequencies [42]. Figure 4: S-band antenna serving as the ground for an X-band array in a dual-frequency S-/X-band design [40].