Compact UWB Slot Antenna Utilizing Traveling-Wave Mode Based on Slotline Transitions

A compact ultra-wideband (UWB) slot antenna using narrow slots is proposed. Different from the traditional wideband slot antennas with multiple resonant modes, the proposed design of this paper utilizes the traveling-wave mode. By using a slotline–CPW transition as the convertor, which connects a slotline and four open slots, the forward wave in the slot has small reflection. The working mode keeps stable at different frequencies, i.e., operating in the traveling-wave mode. As a result, both wide bandwidth and stable radiation patterns are achieved with inherent characteristic of traveling-wave mode. The proposed antenna occupies a small area and the slot width is narrow, which make it suitable to be mounted on the edge of metallic surface for wireless devices. Given an instance for validation, a prototype is fabricated, with a slit width of 0.2 mm and a total size of <inline-formula> <tex-math notation="LaTeX">$25\times 30\times 0.762 $ </tex-math></inline-formula> mm³ (<inline-formula> <tex-math notation="LaTeX">$0.24\times 0.29\times 0.007 \lambda _{L0}^{3} $ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$\lambda _{L0} $ </tex-math></inline-formula> is the wavelength in free space at the lowest operating frequency). Measured results show that a relative bandwidth (VSWR < 2) of about 121% is achieved, covering the entire UWB. Besides, stable gains and radiation patterns are obtained in the operating band. The time-domain characteristic is also investigated, and a small-signal distortion is achieved.