A Miniaturized Tree-Shaped Fractal Antenna Printed on a Flexible Substrate: A Lightweight and Low-Profile Candidate With a Small Footprint for Spaceborne and Wearable Applications

In this article, an inkjet-printed tree-shaped fractal antenna (FA) with a small metal footprint is presented along with its method of fabrication on a flexible substrate. The antenna includes a tree-shaped fractal part, a tapered matching line, and a coplanar waveguide (CPW) line with filleted grounds. The fractal tree is formed by repeating a scaled V-shaped unit cell in each iteration. As the fractal iterations of the antenna are increased, the resonance frequency of the antenna shifts in a large range of frequencies while its radiation properties, dimension, and metal footprint remain almost constant. Six different versions of the proposed FA were fabricated by an inkjet printer on a flexible substrate, and their characteristics were measured. Simulation and measurement results showed that a 16% increase in the antenna's metal footprint shifts the resonance frequency from 16.38 GHz to 5.08 GHz. The shift of 3.22 times of the resonance frequency after four iterations is 61% higher than the state of the art of tree-shaped FAs in the literature. The proposed FA provides a 1.36-GHz bandwidth (BW) and a torus-shaped far-field radiation pattern with a 92° half-power beamwidth (HPBW) in the azimuth direction at 5.08 GHz, whereas the wavelength-normalized metal footprint is 87% smaller than a rectangular patch antenna and at least 60% smaller than other similar FAs. The area of the proposed antenna is more than 3.54 times smaller than similar FAs in the literature. The proposed flexible FA weighs about 2.08 g, of which 1.54 g is the weight of its SMA coaxial connector. The antenna thickness is 130 µm. The lightweight construction and low profile of the miniaturized antenna make it a good candidate for spaceborne and wearable applications.