In this paper, a long-range underwater EM communication system is proposed based on ultra-compact ELF magneto-mechanical transmission antenna (UEMTA). The transmitter mainly includes waveform generator, variable frequency drive (VFD) and a three-phase induction motor. And the receiver consists of a 200-turn coil and signal analyzer. Based on the equivalent model of rotating magnetic dipole, the principles of the EM transmission underwater and across the interface of water and air are analyzed. ELF wave propagating under water in the adjacent area was stronger and decays slowly, which was certificated by the experiment and simulation. So, the long-range transmission underwater in ELF band with digital coding modulation based on the UEMTA is realized, and the longest distance can reach 210 m under water in the experiment. The transmission of ELF wave across water-air medium based on the system is also tested by the experiment too. The long-range transmission of digital coding modulation across the water air interface is realized with the longest distance about 210 m. The ELF transmission technology based on the UEMTA can greatly promote the flexible long-distance underwater transmission, the development of satellite-to-submarine communication and ocean exploration.

A 2-D scanning phased array with large element spacing using pattern reconfigurable stacked patch antenna at Ka-band is presented. The pattern reconfigurable stacked patch antenna is composed of four patches on the top integrated with four p-i-n diodes and a driven patch on the lower layer, where the top patches are located along the diagonals of the proposed antenna. By switching the reverse/forward bias states of p-i-n diodes, the phase gradients in different directions are generated and beam steering on the E-, D-(diagonal), and H-planes can be delivered. Subsequently, a 2-D scanning $4\times 4$ phased array with large element spacing is proposed by applying the pattern reconfigurable stacked patch antenna. The 2-D space is divided into nine subsets and covered by nine states of the proposed antenna. The measured results show that a scanning range of ±55° on the E-, D-, and H-planes can be provided. The maximum realized gain is 20.9 dBi at 26.5 GHz with an aperture efficiency of 62.0%. Compared with conventional half-wavelength phased array, the complexity and cost can be reduced for 2-D scanning phased array by introducing the proposed pattern reconfigurable stacked patch antenna.

A novel dual-port phase antenna is proposed to realize 2-D scanning. The antenna consists of two monopoles on both sides and a fishbone structure in the middle. By changing the phase difference ${\Delta \varphi }$ between two monopoles, energy is coupled to the proposed structure, exciting different degrees of superposition of even and odd modes. The continuous switching from the broadside lobe to the end-fire lobe is realized, and it has the characteristic of 2-D scanning. Furthermore, to provide an in-depth insight into the 2-D scanning mechanism, two linear arrays (Array 2 and Array 3) based on the proposed antenna element and a generalized principle of pattern multiplication (GPPM) are developed. The fabricated Array 2 can offer scanning angles of 0°–73° along the $\theta $ -direction with the gain of 6.5–10.4 dBi and 90°–140° along the $\Phi $ -direction with the gain of 6.1–11.7 dBi. Its scanning coverage of 3 dB beamwidth is $0^{\circ } < \Phi < 140^{\circ }$ , $0^{\circ } < \theta < 90^{\circ }$ . The manufactured Array 3 can scan 0°–90° along $\theta $ -direction with the gain of 8.2–11.1 dBi and 50°–90° along the $\Phi $ -direction with the gain of 6–9.36 dBi, and its 3 dB coverage of the main beam scanning is $0^{\circ } < \Phi < 180^{\circ }$ , $0^{\circ } < \theta < 90^{\circ }$ . Consequently, the proposed antenna and GPPM can be readily extended to wide-angle scanning phased arrays.

A novel millimeter-wave (mm-Wave) binary coding antenna with broadband, dual-polarization, and wide beamwidth is proposed, and its broad-angle scanning array is also studied. The element employs the stacked patches, where the optimal middle parasitic patch and top driven patch are introduced to broaden the bandwidth and beamwidth. The driven and parasitic patches are realized by series of small units optimized by binary code. The measured results for the proposed antenna prototype agree well with the simulated ones, showing a wide impedance bandwidth and good port isolation from 21.8 to 33.2 GHz (FBW = 41.5%). The measured half-power beamwidth is between 128 $^{\circ }$ and 157 $^{\circ }$ over the operating bandwidth. The element was then extended to an eight-element phased array. The measured results demonstrate that the array with a broad scanning angle more than 100 $^{\circ }$ over the available band can be achieved.

A novel low-profile phased antenna with dual-port and its two types of 1-D linear array to 2-D space wide-angle beam scanning are proposed. The antenna unit is composed of fishbone structure and rhombus parasitic patch, which is folded into n-shaped to low profile $0.08\lambda $ . By adjusting the phase difference ( $\Delta \varphi$ ) from 0° to 180°, the antenna working mode is changed from even mode to hybrid mode and to odd mode eventually. Therefore, the proposed antenna unit realizes wide-angle scanning characteristics and continuous switching state from broadside lobe to endfire lobe. Furthermore, the proposed phased antenna element is extended to two kinds of 1-D linear phased array (Array#1 and Array#2) based on the generalized principle of the pattern multiplication. The fabricated Array#1 can realize beam scanning range $- 116^{\circ }< \theta _{\mathrm {m}} < 0^{\circ }$ ( xo z plane), $0^{\circ }< \theta _{\mathrm {m}} < 63^{\circ }$ ( yo z plane), and $90^{\circ }< \Phi _{\mathrm {m}} < 169^{\circ }$ ( xoy plane) and the fabricated Array#2 can achieve $0^{\circ }< \theta _{\mathrm {m}} < 60^{\circ }$ ( xo z plane), $0^{\circ }< \theta _{\mathrm {m}} < 65^{\circ }$ ( $\text{y}{o}\text{z}$ plane), and $90^{\circ }< \Phi _{\mathrm {m}} < 152^{\circ }$ ( xoy plane). The proposed phased antenna unit and its 1-D array can realize 2-D space wide-angle scanning, improving scanning performance and expanding scanning dimensional space in phased array.

A magnetic Yagi-Uda antenna applying higher-order mode in millimeter-Wave band with vertically polarized endfire radiation is proposed in this paper. Surface wave mode analysis is applied to spot TE mode for magnetic Yagi-Uda antenna in contrast to TM mode for electric Yagi-Uda antenna. A modified structure evolved from conventional U-shaped cavity is used to address the reversed current issue for higher order mode, which exhibits a more uniform phase distribution at the Yagi-Uda array end. Then a composite end-feeding structure with reflector integrated is further introduced to minimize its parasitic effects for practical antenna design in millimeter-wave band. To validate the design, a prototype with a size of 2.7λ0×1.25λ0×0.088λ0 is fabricated and tested. It can achieve an endfire gain of 8-11 dBi within 24-26 GHz with -10-dB impedance band covering an even wider frequency range. The measured front-to-back ratio (FBR) is larger than 16.1 dB. Vertically polarized radiation is realized with cross-polarization level lower than -20 dB at endfire direction.