Ultra-wideband antenna designed for stealth aircraft

Chinese researchers have designed a compact, high-performance antenna that can seamlessly integrate into modern stealth aircraft, enabling efficient communication and navigation without compromising radar invisibility or aerodynamic performance.

As stealth capabilities and aerodynamic performance become essential, modern combat aircraft are being designed with flatter profiles to minimise their radar signature and improve aerodynamic efficiency. These aircraft feature a flying wing design that resembles a flat plate and a tail-less configuration, significantly reducing the surface area detectable by radar. However, these sleek designs pose challenges when integrating communication and navigation systems.

Traditional antennas, which are bulky and protrude from the aircraft, can be easily detected by radar. To maintain both stealth and aerodynamic performance, compact antennas that seamlessly integrate into the aircraft’s structure are increasingly necessary. Currently, antennas as small as 5 mm can be built into the surface of aircrafts; however, these antennas typically operate within a narrow frequency range of 2.3–2.5 GHz. To cover a wider range (150–600 MHz), the antenna’s height needs to be increased to 0.39 times the wavelength, making it much larger than the original 5 mm size.

Researchers from the Southwest China Institute of Electronic Technology and the University of Electronic Science and Technology of China (UESTC) have now introduced an omnidirectional circular ring antenna that is both ultra-wideband and low profile. The antenna has a profile height of just 0.047 times the low-frequency wavelength, making it significantly smaller and capable of covering a broader frequency range. Their work has been published in the Journal of Electronic Science and Technology.

“We propose an airborne ultra-wideband circular ring conformal array antenna based on the typical tightly coupled ultra-wideband long slot element and traditional miniaturisation methods of omnidirectional antennas,” said team leader Associate Professor Feng Yang, from UESTC.

The research team achieved miniaturisation by extending the current path of the antenna, effectively making it electrically longer than its physical size. The design features two tightly coupled dipole antennas arranged in a circular pattern, with the H-plane (corresponding to the magnetic field) aligned with the array’s direction. Each antenna is designed with a long slot opening, which shapes the current flow and enables the antenna to operate across a broad frequency range. The elements are fed with equal in-phase power, ensuring consistent signal strength across all elements.

To achieve a low-profile design, the antenna uses two elements connected with a power divider along the E-plane (electric field) direction. However, using only two elements leads to edge effects, such as current loss at the edges and impedance mismatch. To resolve this, they incorporated a short-circuit wall, which reflects electric fields like a mirror and helps to control the current flow along the antenna. They also placed lumped resistors in the gaps of the wall to absorb edge reflected waves.

To further reduce ground reflection interference, the researchers positioned a resistive frequency-selective surface between the antenna and the metal ground. Simulations showed that this surface absorbs over 30% of the reflected energy, especially at higher frequencies where interference is most severe, thereby improving overall performance.

The result is a highly compact, ultralow-profile omnidirectional circular array with eight elements, featuring a height of only 0.047 times the low-frequency wavelength and a lateral diameter of 0.19 times the wavelength. The antenna operates across a broad frequency range, achieving an impedance bandwidth close to 12:1 while maintaining an active voltage standing wave ratio (VSWR) consistently below 3, indicating efficient performance with minimal energy loss. Additionally, it ensures good omnidirectional radiation characteristics, with gain patterns controlled within 3 dB across the entire operational bandwidth, making it ideal for multifunctional airborne antenna applications.

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