## 3 Antennas with General Aspects Utilized for CubeSat
### Planar Phased Patch Antennas and Their Arrays
A major benefit of this design is its capacity to electronically direct the beam, providing adaptable and dependable communication links. The proposed antenna was installed on a GND layer with dimensions of 80 \(\times\) 80 mm\({}^{2}\), with each dipole measuring enough spacing between them. The antenna achieved a 5.03 dBi gain, \(-27.35\) dB for S\({}_{11}\), and a 4.8% BW. Nevertheless, its primary drawback is its considerable size, occupying substantial areas on the CubeSat--80 mm \(\times\) 80 mm on each side. Its large dimensions potentially limit the space available for other components. In Ref. [28], a compact planar dipole antenna with a square form for 1U CubeSats was designed to incorporate four array elements linked through a phase-shifting network. To maintain a balanced power distribution, a balun was positioned beneath each dipole. This configuration produced circular polarization (CP), ensuring a stable communication link even as the CubeSat reoriented in space. It had compact dimensions of 55 mm \(\times\) 55 mm and exhibited bidirectional radiation. It achieved a broad bandwidth of 33.46% and a 3.49 dBi gain. The primary benefit of this design is its small size coupled with a wide bandwidth. Regarding the bandwidth, the antenna in Ref. [28] outperformed the dipole antenna. Nonetheless, a major limitation is the relatively low gain, which might constrain the communication range or performance compared to higher-gain designs. Another major limitation is the complexity of the deployment mechanisms. Among the designs, the one in Ref. [29] distinguishes itself by having achieved the highest gain of 48.7 dBi in the Ka-band (34.2-34.7 GHz), exceeding the gains of other systems. The researchers introduced an X-band CP 2 \(\times\) 2 annular array of patches developed for a 1U CubeSat. The main innovation involves grounding by short-circuiting it to the GND layer with six pins to accomplish CP. Furthermore, the array elements are energized by a ring resonator positioned at the array's center, which is connected to all four patches via strips. It employs a sequential phase feeding network, yielding a broad BW of 16.97% and a total gain of 13 dBi. However, the researchers only presented simulation results for this design [30]. In Ref. [31], the authors present a transparent dual-band patch antenna array designed for a 3U CubeSat, operating at frequencies of 8 GHz and 11.2 GHz. The innovative aspect of this design is the implementation of a transparent patch on a glass substrate, allowing it to be placed above solar cells. This configuration maximizes the space available for solar cells while enabling sunlight to reach them. The antenna consists of an 8 mm \(\times\) 8 mm top patch layer for the 11.2 GHz frequency, which is fed via two probes from a coupler at the bottom layer. Beneath this, a 6.3 mm \(\times\) 6.3 mm patch serves the 8 GHz frequency and is fed from the top patch layer. A dual-band coupler provides two inputs with a 90\({}^{\circ}\) phase shift, facilitating both right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP). However, the proposed antenna has notable limitations, such as exceptionally high reflection coefficients of \(-19\) dB at 8 GHz and \(-15.5\) dB at 11.2 GHz. These values indicate that a significant amount of power is reflected rather than radiated into space, which can impact the overall efficiency of the communication link. To mitigate this, shorting walls and pins can reduce the antenna size without compromising performance aspects like gain, bandwidth, and impedance matching. Ref. [32] introduced a multifunctional, high-gain, and circularly polarized (CP) transparent subarray patch antenna tailored for CubeSat remote sensing applications. Operating in the X-band, the antenna has a compact size of 10 mm \(\times\) 10 mm. The design comprises a 2 \(\times\) 2 subarray with two layers and a cross-slot etched into the bottom ground plane.