X-band antennas are often used for dense satellite communications payloads. They handle the data transmission of high-resolution captured and detected images from a satellite to a ground station. Instead of a conventional microstrip line antenna for such applications, however, a substrate-integrated-waveguide (SIW) -based antenna array has been proposed and analyzed in several configurations at Korea Aerospace University. The arrays were fabricated as multilayer printed-circuit boards (PCBs) for right-handed circular polarization (RHCP) by a team of researchers comprising Eun-Young Jung, Jae W. Lee, Taek K. Lee, and Woo-Kyung Lee.
Specifically, the researchers proposed, designed, and investigated arrays based on a single element using two types of array antennas centered on SIW-based design. To increase the transmission efficiency between the satellite and ground system while enhancing antenna gain, for example, they introduced the design procedure, simulation, and measured data of SIW-based 2x2 and 2x4 array antennas. These arrays build on a single element operating at X-band from 8.0 to 8.5 GHz. The single-element approach had to overcome issues like feeding loss, undesirable radiation, and the reduced efficiency brought on by the use of a hybrid-coupled and series-microstrip feeding structure. For RHCP generation, a novel SIW-based and cavity-backed ring-slot antenna was combined with a SIW and coaxial feeding network, which has low-loss and broadband impedance-matching characteristics.
To design the single-element 2x2 antenna array, the team had to design a power divider providing equal amplitude at each output port in that array. That SIW-based, four-way power divider was designed and measured as a replacement for the microstrip structures. To further increase antenna gain and improve RHCP quality, a 2x4 antenna array with an eight-way power divider also was designed and investigated. By selecting the optimum amplitudes for each element’s resonant frequency, the SIW-embedded, eight-way power divider satisfied equal division at all output ports.
Finally, a 2x4 antenna array was proposed to improve RHCP gain and enhance CP quality with a sequential feeding scheme. This antenna had eight radiating elements in the top layer, an eight-way power divider, and phase-delay lines in the bottom layer. The researchers reported notable improvements in electrical performance—especially regarding the reflection coefficient bandwidth, antenna gain, and axial ratio bandwidth. See “SIW-Based Array Antennas with Sequential Feeding for X-band Satellite Communication,” IEEE Transactions On Antennas And Propagation, Aug. 2012, p. 3632.