A new geometry for uniplanar, ultra-wideband monopole antenna has been proposed for operations in the 1.8–30 GHz band, thanks to its fractal structure in the form of a cardioid. The antenna has extremely small dimensions at 0.21$\lambda$ × 0.285$\lambda$ at the lowest frequency of 1.8 GHz. A parametric analysis of the influence of certain antenna dimensions on its characteristics was performed in order to achieve the widest possible impedance bandwidth. This antenna is designed for low-cost FR-4 substrate because it is primarily intended for use in broadband energy harvesting and IoT systems, but it is also suitable for applications in communication systems. Simulation results show that the antenna has a reflection coefficient $\left(S_{11}\right)$ below −10 dB in the entire 1.8 GHz to 30 GHz frequency range, which covers all existing cellular bands: 3G, 4G, 5G Wi-Fi, ISM, satellite communication and radar bands. The antenna exhibits gains up to 5 dBi.

In this paper, the analysis of the influence of the ionosphere on the propagation of chaotically modulated electromagnetic waves is performed. Differential chaotic shift keying is very useful as communication system. Chaotic modulations with discrete chaotic systems such as tent map, logistic map and PWAM map were realized. The robustness of chaotic signals to changes that occur during their passage through the turbulent ionosphere was investigated. Time delays as well as phase and frequency offset of chaotic signals were compared. Simulations and modeling of the communication system were performed in MATLAB Simulink.

This paper presents a compact ultra-wideband (UWB) printed monopole antenna based on fractal cardioid geometry, designed to operate over the 4–30 GHz frequency range. The proposed antenna is intended for multi-service wireless applications, including IoT, WLAN, WiMAX, and satellite communications, while also being suitable for RF energy harvesting systems. Driven by the increasing density of wireless devices and ambient electromagnetic radiation, modern antenna systems are required to efficiently cover multiple frequency bands with a single compact structure. To address these requirements, the proposed antenna employs a fractal cardioid-based radiating element enabling significant bandwidth enhancement without increasing antenna size. The antenna is fabricated on a low-cost FR-4 substrate and experimentally validated. The measured results show good agreement with the simulated results, confirming the robustness of the design. The antenna achieves \(S_{11}\) below − 10dB across a wide portion of the SHF band, with stable radiation characteristics, gain up to 5 dBi, and efficiency up to 80%. In addition, the antenna exhibits favorable impedance characteristics suitable for direct integration in rectenna systems without requiring a matching network. Owing to its compact dimensions, electrically small profile, low cost, ultra-wideband performance, and experimentally verified reliability, the proposed antenna is suitable for integration into next-generation IoT devices, multi-band communication systems, and RF energy harvesting applications.

This paper presents a proposal for a new chaotic-based underwater acoustic modulation scheme. The proposed method is a differential chaotic shift keying modulation based on the Lorenz attractor. Unlike conventional techniques that use Chirp signals, synchronization is achieved using a chaotic signal. In the demodulator, a Doppler shift compensator is also implemented, capable of compensating shifts up to 10 m/s. This compensator is based on bank of Doppler shifts. In order to see the influence of underwater acoustic channel on the proposed acoustic signal, the simulations are performed. The channel was modeled by adding white Gaussian noise with a signal-to-noise ratio (SNR) ranging from -5 dB to 20 dB, multipath propagation with 7 received waves, and the Doppler effect with a speed of ±10 m/s.The experimental verification of the proposed waveform was conducted in an anechoic tank at the SEA Laboratory at the University of Newcastle, as well as during sea trials in Kumbor, Montenegro. The experiments tested the influence of high impulsive noise generated by crustaceans and the presence of high noise generated by vessels. Simulation results and experimental verification demonstrated that the proposed modulation technique is resistant to underwater noise, both Gaussian and impulsive, and is suitable for operation in complex channels with significant multipath fading and attenuation. Furthermore, it offers the advantage of being environmentally friendly.