A design of high-gain end-fire antenna based on split-ring resonator structures

Vivaldi antennas have wide applications in practice due to the ultra-wide band properties; however, their gain and directivity are relatively low. In this paper, a new method is presented to improve the gain and directivity of Vivaldi antennas in a broad band using split-ring resonator (SRR). Based on the peculiar electromagnetic properties of SRR, a novel high-gain SRR-Vivaldi end-fire antenna in C and X bands is designed and fabricated. The size of the antenna is only 0.33λ ×0.33λ ×0.013λ, a significant miniaturization. Equivalent analysis method has been adopted to study the resonance characteristic of an SRR structure. By adding the SRR structures the singular metamaterials in the front of the Vivaldi antenna have an exponential taper slot, and the SRR structures can play a role as a director which has the ability to enhance the antenna's directivity so that the surface currents will focus on the end-fire direction. The SRR structures have been analyzed, designed, and fabricated, which can be embedded into the original Vivaldi antenna smoothly and compactly. As a result, the gain of the SRR-Vivaldi antenna are enhanced effectively, while the size and bandwidth of the original antenna can be kept, with the reflection coeffcient less than -10 dB from 4 to 13.6 GHz after using SRR. The novel Vivaldi antenna based on the SRR has good features of high gain, high directivity, low return loss and low cross-polarization. Compared to the original Vivaldi antenna, the simulation and measured results demonstrate that the gain of the novel SRR-Vivaldi antenna in C band has been increased by an average value of 75.44% and the half-power beam width has been decreased by 20 degrees in xoy and xoz planes. Meanwhile, the gain has been increased by an average value of 24.46% in X band and the half-power beam width has been decreased by 25 degrees in xoz plane. Testing result of the fabricated antenna demonstrates the reliability of the design. A good agreement between simulations and measurements is obtained. The design owns the merits of low cost, simple design and ease in fabrication and conformation, thus provides a new idea for end-fire antenna gain and directivity improvement. The new antenna has great potentials in applications.