In this paper, we initially construct an equivalent epsilon-near-zero (ENZ) medium by utilizing an air-filled waveguide operating at its cutoff frequency. Following this, based on the principle of dielectric doping, we doped the metal medium into the ENZ waveguide cavity to realize a waveguide epsilon-mu-near-zero (EMNZ) medium. To apply it to antenna design, an array of slots is transversely etched along the sidewall of the EMNZ waveguide to radiate electromagnetic wave outwards, thereby constructing an equal spacing 10-element antenna array featuring a simplified feeding network and impedance matching, with simulation confirmed the antenna's strong directivity. We have optimized the element spacing using genetic algorithm, achieving a low reflection coefficient while concentrating the elements in the main lobe direction, which has successfully decreased the side lobe level to -22.01 dB and enhanced the peak gain to 14.01 dBi. As measured, the optimized equal spacing antenna array operates at the frequency point of 4.986GHz (-10dB impedance bandwidth less than 0.1%), but it achieves a radiation efficiency of 90.8% within a length of 5λ and a strong directivity, making it applicable to fields such as radar detection and satellite communication. Moreover, we explored the two-dimensional form and the deformability of the EMNZ antenna array, achieving a 7×10 planar antenna array with a gain of 21.3dBi and a folded antenna array with an extremely low side lobe level of -35.7dB, further expanding its application prospects.

Very-low-frequency (VLF) electromagnetic waves (3–30 kHz) are stable and attenuated, suitable for various applications in submarine communication and earthquake prediction. Very-low-frequency electromagnetic waves usually propagate in atmospheric waveguides formed between the anisotropic ionosphere at low to medium heights and the earth. However, the electromagnetic parameters of the anisotropic ionosphere at low to medium heights are very complex, making it difficult to accurately calculate and analyze the scattering characteristics of very-low-frequency electromagnetic waves. This article divides the mid to low altitude anisotropic ionosphere into fine layers, and establishes a more accurate transmission model for ultra-low-frequency electromagnetic waves in the layered structure of ionization layers by deriving the anisotropy/transmission matrix of each layer. In the comparative verification, we calculated the field strength of 17 kHz VLF electromagnetic waves within a transmission distance range of 500–1600 km based on the proposed method and compared it with statistical data collected from actual communication experiments and theoretical calculation results based on traditional ITU-R P.372-11. The results show that compared with the theoretical results based on ITU-R P.372-11, the method proposed in this paper fully considers the vertical height non-uniformity of the ionosphere, and its calculated results are more consistent with actual measurement data, with higher accuracy. Our work provides excellent guidance for the development of precise models for the propagation and prediction of extremely low-frequency electromagnetic waves, as well as a good idea for the accurate calculation of VLF electromagnetic scattering within 500–1500 km.

To address the inherent contradiction between low-profile design and high gain in traditional omnidirectional antennas, as well as the narrow bandwidth constraints of ENZ antennas, this study presents a dual-mode ENZ-FP collaborative resonant antenna array design utilizing a substrate-integrated waveguide (SIW). Through systematic analysis of ENZ media’s quasi-static field distribution, we innovatively integrated it with Fabry–Perot (F–P) resonance, achieving unprecedented dual-band omnidirectional radiation at 5.18 GHz and 5.72 GHz within a single ENZ antenna configuration for the first time. The directivity of both frequencies reached 12.0 dBi, with a remarkably low profile of only 0.018λ. We then extended this design to an ENZ-FP dual-mode beam-scanning array. By incorporating phase control technology, we achieved wide-angle scanning despite low-profile constraints. The measured 3 dB beam coverage angles at the dual frequencies were ±63° and ±65°, respectively. Moreover, by loading the impedance matching network, the −10 dB impedance bandwidth of the antenna array was further extended to 2.4% and 2.7%, respectively, thus overcoming the narrowband limitations of the ENZ antenna and enhancing practical applicability. The antennas were manufactured using PCB (Printed Circuit Board) technology, offering high integration and cost efficiency. This provides a new paradigm for UAV (Unmanned Aerial Vehicle) communication and radar detection systems featuring multi-band operation, a low-profile design, and flexible beam control capabilities.

In order to break through the difficulties with a very-low-frequency (VLF) miniaturized antenna with small power capacity and low radiation efficiency, this paper proposes a high-radiation-field-strength magnetic loop antenna based on a nanocrystalline alloy magnetic core. A high-permeability nanocrystalline toroidal core (μ_r = 50,000, B_s = 1.2 T) is used to optimize the thickness-to-diameter ratio (t = 0.08) and increase the effective permeability to 11,000. The Leeds wires, characterized by their substantial carrying capacity, are manufactured through a toroidal winding process. This method results in a 68% reduction in leakage compared to traditional radial winding techniques and enhances magnetic induction strength by a factor of 1.5. Additionally, this approach effectively minimizes losses, thereby facilitating support for kilowatt-level power inputs. A cascaded LC resonant network (resonant capacitance 2.3 μF) and ferrite balun transformer (power capacity 3.37 kW) realize a 20-times amplification of the input current. A series connection of a high-voltage isolation capacitor blocks DC bias noise, guaranteeing the stable transmission of 1200 W power, which is 6 times higher than the power capacity of traditional ring antenna. At 7.8 kHz frequency, the magnetic field strength at 120 m reaches 47.32 dBμA/m, and, if 0.16 pT is used as the threshold, the communication distance can reach 1446 m, which is significantly better than the traditional solution. This design marks the first instance of achieving kilowatt-class VLF effective radiation in a compact 51 cm-diameter magnetic loop antenna, offering a highly efficient solution for applications such as mine communication and geological exploration.

Short-wave communication, operating within the frequency range of 3–30 MHz, is extensively employed for long-distance communication because of its extended propagation range and robustness. The ionosphere undergoes complex transformations when influenced by the geomagnetic field, evolving into an uneven and anisotropic electromagnetic medium. This complex property makes the transmission of electromagnetic fields within the ionosphere extremely complex, posing significant challenges for accurately evaluating electromagnetic scattering phenomena. To address the aforementioned challenges, this paper proposes a new method for calculating short-wave ionospheric scattering based on a complex anisotropic multilayer medium transmission matrix. Firstly, by utilizing the characteristic changes of ionospheric electron density with height, the ionization layer is divided into multiple horizontal thin layers, each with an approximately uniform electron density, forming a multilayer horizontal anisotropic structure. Subsequently, the scattering characteristics of electromagnetic waves in the ionosphere were calculated using the transmission matrix approach. The results calculated using this method are consistent with actual measurement values and superior to traditional short-wave ionospheric transmission calculation methods.

To address the issues of high loss and low efficiency in feeding networks of conventional antenna arrays at millimeter-wave frequencies, this letter presents a high-gain endfire antenna array with shared apertures based on the epsilon-near-zero (ENZ) mode. We introduce shorting vias at the horn aperture based on composite right/left-handed transmission line (CRLH TL) theory, enabling ENZ mode operation in the non-uniform aperture with broadened bandwidth, which surpasses the bandwidth limitation of conventional waveguide ENZ antenna. A SIW operating in the ENZ mode is employed as the feeding network, which excites a four-element shared-aperture array through slot coupling. A dipole array integrated with a reflective structure is introduced to create a magneto-electric complementary radiation mechanism, thereby enhancing endfire gain. The radiation pattern function of the antenna is derived and validated through full-wave simulations and measurements. Measured at 24.39 GHz, the prototype exhibits a peak gain of 12.03 dBi, a total efficiency of 84.2%, and a sidelobe level of -21.1 dB under an in-phase excitation via a single feeding point. The proposed design provides a high-performance, low-cost, and compact endfire antenna solution for millimeter-wave communication, radar, and satellite systems.