# Novel Beam Scan Method of Fabry-Perot Cavity (FPC) Antennas
###### Abstract  
A new beam scanning method of a Fabry-Perot cavity (FPC) antenna is proposed. To obtain high gain in a target direction with a reduced sidelobe level (SLL), we devised a tapered partially reflective surface (PRS) as a superstrate. Moreover, to attain various beam scanning directions, a phase-controllable artificial magnetic conductor (AMC) ground plane with a broad reflection phase range and high reflection magnitudes was introduced. In the proposed method, a new formula to satisfy an FP resonance condition in a cavity for a scanned beam is also suggested. According to the formula, the FTC antenna can precisely scan the main beam in designed target directions with well-maintained high gain, which has been hardly achievable. In addition, our method demonstrates the potential of electrical beam-scanning antennas by employing active RF chips on the AMC cells. To validate the method, we fabricated a prototype FTC antenna for a scanned beam at \(\theta=30^{\circ}\). Furthermore, we conducted an additional simulation for a different beam scanning angle as well. Good agreement between the expected and experimental results verifies our design approach.  
F 103 October 2021 17 November 2021 20 Novemberhigh gain despite its simple configuration [6]. In [7; 8], for example, a combination of the PRS and a phase correcting structure is introduced to enhance. In [9], an FPC antenna using an all-dielectric PRS and PEC walls is studied to realize low profile as well as high gain. Furthermore, in [10], a PRS based on low-cost 3D printing technology is employed to obtain not only high gain, but also polarization reconfigurability.  
However, they have the shortcoming that the antenna cannot achieve a scanned beam. To overcome this issue, some groups have introduced a phase-controllable PRS and obtained beam-steering capability in the FPC antenna. For example, a 3D printed stepped dielectric [11], a fluidically programmable metasurface [12], and an electrical beam-switching metasurface [13; 14; 15] have been suggested as a PRS. Nevertheless, they have several crucial problems such as a low beam-switching speed [11; 12], fluctuating radiation performances depending on the scanning angle [12], and a narrow steering range [13; 14; 15].  
As a solution to these problems, we propose a new beam-scan method of an FPC antenna. The proposed method introduces an artificial magnetic conductor (AMC) ground plane that is based on a newly introduced design formula instead of an optimization used in [16]. Moreover, a tapered PRS is devised to suppress a sidelobe level (SLL), which is practical for a finite antenna size [17]. Compared with the prior works, the strong points of our method are as follows:  
1. A predictable beam-scan direction based on a newly introduced design formula;
2. A wide beam-scan range with a well-maintained high gain;
3. A continuously changeable beam-scan direction.  
To validate our idea, we fabricated and measured a prototype FPC antenna for a scanned beam at \(\theta=30^{\circ}\). Moreover, we performed an additional simulation of a normal radiation (\(\theta=0^{\circ}\)) case as well. Consequently, by comparing simulation and measurement results, we have successfully proven the validity of our design proposal.  
All simulations have been conducted using CST Microwave Studio [18].