Metamaterial-Inspired Electrically Compact Triangular Antennas Loaded with CSRR and 3 × 3 Cross-Slots for 5G Indoor Distributed Antenna Systems

In this article, two distinct kinds of metamaterial (MTM) antennas are proposed for fifth-generation (5G) indoor distributed antenna systems (IDAS). Both antennas operate in the sub-6 GHz 5G band, i.e., 3.5 GHz. The antenna’s radiating structure is based on a combination of triangular and rectangular patches, as well as two complementary split-ring resonators (CSRR) unit-cells etched on the top layer. The bottom layer of the first MTM antenna is a complete ground plane, while the bottom layer of the second MTM antenna is etched by a 3 × 3 cross-slot MTM structure on the ground plane. The use of these structures on the ground plane improves the antenna bandwidth. The proposed antennas are designed using two different substrates i.e., a high-end Rogers thermoset microwave materials (TMM4) substrate (h = 1.524 mm/ε(r) = 4.5/tan δ = 0.002) and a low-end flame-resistant (FR4) epoxy glass substrate (h = 1.6 mm/ε(r) = 4.3/tan δ = 0.025), respectively. The antenna designs are simulated using CST microwave studio, and in the end, the antenna fabrication is performed using FR4 substrate, and the results are compared. Furthermore, parametric analysis and comparative studies are carried out to investigate the performance of the designed antennas. The simulated and measured results are presented for various parameters such as return-loss, gain, and radiation pattern. The two MTM antennas have an overall dimension of 18 × 34 mm(2), demonstrating that the proposed design is 60 percent smaller than a standard microstrip patch antenna (MPA). The two proposed MTM antenna designs with complete ground plane and 3 × 3 cross-slot MTM on the bottom layer using FR4 substrate have a measured gain/bandwidth characteristic of 100 MHz/2.6 dBi and 700 MHz/2.3 dBi, respectively.