A Reflectarray With Low Profile Based on the Method of Choosing the Certain Phase Constant

In this letter, a reflectarray antenna with a small focal diameter ratio (F/D) is presented. It is found that when the F/D is extremely small, the phase constant used in calculating the required reflection phase on the reflecting surface significantly affects the radiation pattern. In certain cases, an unsuitable phase constant can even cause the main beam to split. The unit cell is implemented as a stacked patch, and the reflecting surface comprises 14 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \times $</tex-math></inline-formula> 14 elements. The effect of the phase constant on the radiation pattern is analyzed, and two reflectarrays with phase constants of 90° and 180°, both operating at 10 GHz with an F/D of 0.05, are compared. These two reflectarrays are simulated, fabricated, and measured. The measured results show good agreement with the simulations. Within the operating band, the reflectarray with a phase constant of 90° achieves a maximum measured gain of 20.42 dBi, with the first sidelobe level (SLL1) below −10 dB. The radiation pattern of the reflectarray with a phase constant of 180° is totally distorted, resulting in a measured gain of 6.56 dBi at 10 GHz and an SLL1 of −5.8 dB.