Miniaturized Ultrawideband Half-Mode Vivaldi Antenna Based on Mirror Image Theory

A novel miniaturized ultrawideband (UWB) half-mode Vivaldi (HM-Vivaldi) antenna based on mirror image theory is proposed in this letter. The antenna consists of half a modified radiating arm and two rows of metallized vias, which are equivalent as the perfect electric wall. According to the mirror image theory, the induced current on the electric wall can replace the mirror image current of the radiating arm at its symmetrical position, which will result in the HM-Vivaldi structure. The antenna size of 0.35λ_0L × 0.54λ_0L (λ_0L is the free-space wavelength at the lowest operating frequency) is reduced by 33% compared to the original antipodal Vivaldi antenna size. In addition, the continuous exponential curved edge on the ground is improved to retain the wideband impedance match characteristic. The operation theory and parametric analysis of this HM-Vivaldi antenna are presented with a prototype being measured. An UWB from 5.3 to 40 GHz with the reflection coefficient lower than -10 dB is experimentally achieved except that |S11| is slightly higher than -10 dB at several frequencies, and the maximum gain reaches 11 dBi.

I. Introduction

Multifunction, high capacity, and high data rate of modern wireless communication systems, such as tumor diagnosis [1]–[3], through-the-wall detection [4], and small radar systems [5], [6], require antennas operating in an ultrawideband (UWB) with compact size due to the limited space and high integration of hardware [7]. The Vivaldi antenna, first proposed by Gibson in 1979 [8], and then developed by Gazit [9], is an ideal candidate for these systems. It is a traveling-wave antenna with wide band, high efficiency [10], [11], and stable radiation patterns. However, the antenna size is large.