This paper presents a subwavelength multiband bandstop metamaterial reflector for enhancing antenna gain beyond what is achieved by conventional metallic reflectors. The unit cell was designed to generate multiband stopbands at three frequencies: the first at 1.8 GHz, the second at 2.6 GHz, and the third at 3.5 GHz. The design was implemented on a low-cost FR-4 printed circuit board with a simple design and compact size. The unit-cell structure included a transmission line configuration using the tri-section step-impedance technique, combined with a capacitive load at the end of the transmission line via a double interdigital structure. The structure could control the first, second, and third resonance frequencies to occur at the desired bands and ensured independent resonances. The double interdigital capacitive load significantly increased capacitive loading, generating a strong slow-wave effect along the transmission line structure, exceeding that achieved with conventional capacitive loading techniques. As a result, the transmission line size of the unit cell was drastically reduced from the conventional λ/2 to λ/16. To achieve metamaterial characteristics, the unit cell was modified to exhibit negative permittivity (ENG) for enhanced reflection compared to conventional materials and positive permeability. This was accomplished by adding a rod (ROD) structure behind the main structure using the tri-section step-impedance technique. This configuration generated left-handed current on the structure, resulting in negative permittivity values at all three resonance frequencies. An array of 14 × 14 unit cells was fabricated to form the metamaterial reflector with an overall size of 148 mm × 161.7 mm, which is very compact. The performance was evaluated by placing a single-frequency resonant dipole antenna, operating at the same resonance frequency as the reflector, in front of the reflector along the X-axis plane. The antenna gain increased from approximately 2 dB at all frequencies to about 8 dB. The radiation pattern exhibited directional radiation at 0 degrees. The measured results of frequency responses and antenna gains were close to the simulated results. With superior characteristics and compact size, the proposed metamaterial reflector can be applied for multiband 5G and other modern antenna systems.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)