1536-1225 (c) 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LAWP.2018.2832098, IEEE Antennas and Wireless Propagation Letters > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract—A new design to improve the bandwidth and gain of the dielectric notch radiator is proposed. Rectangular slots are etched on both arms of the antenna to change the current density distribution. More resonant frequencies are created to reduce VSWR value and widen the bandwidth. A parasitic rectangular patch is introduced in the endfire aperture to enhance the electric field coupling and to produce stronger radiation in the endfire direction. Both changes improve the low- and high-frequency band performance, respectively. Evolution of the feeding structures is described in detail. Uniform impedance microstrip line and slotline on the ground are designed to simplify the impedance matching and reduce optimized parameters. The proposed antenna prototype is fabricated and tested with the size of 31.5 mm × 41 mm × 0.508 mm. The measured results show that the bandwidth is 6.75 ~ 16.15 GHz under VSWR ≤ 2, and the corresponding realized gain ranges from 3.52 to 9.44 dBi. The measured radiation patterns are in good agreement with the simulated ones, which validates the design concept. Index Terms—Dielectric notch radiator, endfire antenna, etched slot, parasitic patch, tapered slot antenna. I. INTRODUCTION IDEBAND antennas are desired for many applications such as radar, microwave imaging, and UWB wireless communication systems [1], [2]. Due to the planar structure, wide operating band, and low sidelobe level, Vivaldi antennas are extensively utilized and studied [3]. The Vivaldi antenna belongs to the class of endfire traveling wave antennas, which has theoretically infinite bandwidth and moderate gain. However, the structure is electrically large, up to several wavelengths long, which will limit their applications where the size is a major concern. As a much shorter tapered slot antenna, the dielectric notch radiator attracts significant attentions [4]-[6], whose taper section is less than a wavelength in length. Many techniques were proposed to enhance the radiation performance of the dielectric notch radiator. They can be summarized into four methods: 1) Developing special shapes for radiation arms (e.g., [7]-[9]), such as slotted edges and palm trees; 2) Employing different metamaterials on both sides of the substrate (e.g., [10], [11]), such as placing conductor strip gratings and anisotropic zero-index metamaterials; 3) Utilizing a set of planar directors in front of the aperture of the tapered slot structure (e.g., [12], Manuscript received January 8, 2018. The authors are with the School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798. (e-mail: uscnuaa@gmail.com; yjzheng@ntu.edu.sg). [13]), which can simultaneously increase the gain and size; 4) Loading lumped components in the feeding part to shorten impedance matching length (e.g., [14]). The first method is extensively used in the modified Vivaldi antenna design. In [8], a palm tree antipodal Vivaldi antenna was designed to achieve improved radiative features, e.g., reducing side lobe level and correcting squint effect. In [9], the tapered slot edge with resonant cavity structure was adopted to extend the low-end bandwidth limitation, but lower the gain at higher frequencies. In many reported literatures, some interesting results were achieved, but it still remained challenging to design a variant of wideband Vivaldi antenna with concurrently high gain, compact size, and simple geometry. In this letter, a new design methodology is proposed to improve the performance of the microstrip-fed Vivaldi antenna. The impedance bandwidth is widened by introducing periodic rectangular slots, which are adjacent to the radiating edges and parallel to the endfire direction. A parasitic rectangular patch is employed in the flare aperture to enhance the electric field coupling between the arms. Compared to other modified Vivaldi antenna, the proposed antenna structure improves the gain at the higher frequencies, and reduces the complexity of the impedance matching. An antenna prototype is fabricated and measured to validate the design concept. II. ANTENNA DESIGN CONCEPT A. Antenna Structure Fig. 1 illustrates the geometry of the proposed antenna structure, including the addition of a parasitic rectangular patch and ten etched slots with different lengths and the same widths. It is trapezoid structure on the ground. The antenna is designed and fabricated on the substrate of Rogers RO4350. The substrate thickness is 0.508 mm, its relative dielectric constant is 3.48, and tan is 0.0037. The copper layer is printed on the Improved Design of Vivaldi Dielectric Notch Radiator with Etched Slots and Parasitic Patch Wensong Wang and Yuanjin Zheng, Senior Member, IEEE W L1 b a e j k m n R r θ w1 g1 g2 g3 g4 g5 g6 g7 L2 w2 β l1 l2 5 4 3 2 1 z x (a) (b) Fig. 1. Geometry of the proposed performance-enhanced Vivaldi antenna. (a) Top view, (b) bottom view.