Scientists from the University of Montenegro, the University of Belgrade, and the Academy of Engineering Sciences of Serbia have developed a compact ultra-wideband antenna capable of operating in the frequency range from 4 to 30 GHz. With dimensions of just 18.5 × 25 mm, it can be used for Internet of Things systems, satellite communications, wireless data transmission, bio-radars, and even devices that harvest energy from ambient radio waves.
Modern wireless devices support an increasing number of communication standards, each using its own frequencies. As a result, engineers often have to install multiple antennas, which increases the size and cost of electronics.
The scientists achieved ultra-wideband operation in a single compact antenna thanks to a new fractal geometry of the radiator based on a cardioid – a heart-shaped curve. Inside the large cardioid, the researchers placed a smaller copy of it. This design creates multiple overlapping resonances, allowing the small antenna to operate effectively across a very wide frequency range and replace several specialized antennas.
The antenna is fabricated on an FR-4 fiberglass substrate – the standard material used for most printed circuit boards in electronic devices. During development, the scientists sequentially varied the dimensions of the outer and inner cardioids, the feed line position, and other parameters to achieve the widest possible operating range without increasing antenna size. Subsequently they manufactured a prototype.
Tests confirmed that the antenna efficiently transmits and receives radio signals. About 80% of the power supplied to it is converted into radio radiation rather than lost within the structure. The maximum gain was 5.6 dBi, meaning that in the direction of strongest radiation, the signal is approximately 3.6 times more powerful than that of a hypothetical antenna radiating uniformly in all directions.
According to the researchers, the development is particularly promising for two areas.
The first is energy harvesting systems that capture ambient radio-frequency radiation. The antenna simultaneously receives signals from multiple wireless services, allowing more efficient use of the weak electromagnetic radiation from mobile networks, Wi-Fi, and other sources to power low-power sensors. In addition, it can be connected directly to a rectifying diode without complex matching circuits, simplifying the device design and reducing energy losses.
The second area is compact Doppler radars capable of non-contact monitoring of breathing, heart rate, sleep, or human presence in a room. Thanks to low mutual coupling between closely spaced antennas, such systems can operate with greater accuracy.
