The plasma in contact with liquids has led to various novel applications such as plasma biomedicine, material synthesis, and so on. However, the phenomenon of evaporation under plasma treatment and its impact on plasma–liquid interactions has a limited understanding. In this study, the spatially and temporally resolved behavior of water vapor production and its induced influences on plasma properties and gaseous chemistry were studied in detail in an atmospheric pressure pin‐to‐water pulsed He discharge. Diagnostic methods such as laser‐induced fluorescence (LIF) and high‐resolution optical emission spectroscopy (OES) were applied to determine the water vapor and OH radical densities, as well as key plasma parameters such as the gas temperature and electron density. It shows that the physicochemical properties of plasma vary among different discharge regions due to evaporation behavior stimulated during the pulsed discharge‐on phase. In addition, using simulation based on the experimental data, the mechanisms of how water vapor affects the observed spatiotemporal behaviors of OH radicals in different discharge regions are understood. Compared to the pin‐anode and liquid‐cathode sheath regions, proper electron parameters such as density and temperature, as well as water vapor density in the plasma‐positive column, significantly enhance the production of reactive OH radical through the dominant path of electron‐stimulated H2O dissociation. However, higher levels of electron parameters in the intense discharge region near the positive‐pin boundary enhance OH dissociation and finally result in the hollow distribution of OH density. From the global kinetic plasma simulation, the production of reactive hydroxide species playing key roles in plasma medicine treatments, such as O, H, HO2, H2O2, and hydrated ions including H+(H2O)4 and H+(H2O)5, are promoted noticeably as a result of the enhanced water evaporation process.

A new technology for expanding the axial ratio (AR) bandwidth of the circularly polarized (CP) dielectric patch (DP) antenna while maintaining the low‐profile characteristic is proposed for the first time. By making full use of the multimode characteristic of the DP resonator, two pairs of degenerate modes (ie, TM101 and TM011, TM121 and TM211) are selected for the broadband design. The key to the proposed technology is that according to the EM field distribution of the two pairs of degenerate modes, four air holes are introduced in the DP and their position and size are elaborately designed to discriminately control the frequency of the two pairs of degenerate modes. Then, these modes become close and are merged to effectively expanding the AR bandwidth of the low‐profile CP DP antenna. For demonstration, a prototype centered at about 10 GHz is designed, fabricated, and measured. The measured results exhibit that the proposed CP DP antenna with a low profile of 0.07λ0 owns a 3 dB AR bandwidth of 9.7% and a peak gain of 7.66 dBic. Good agreement is observed between simulated and measured results.

A bandwidth (BW)‐reconfigurable filtering microstrip patch (MP) antenna is investigated in this paper. Two pairs of slots with different lengths are etched on the patch to not only bring two radiation nulls for good filtering performance but also generate additional high resonant mode for extending the operating BW of the antenna. A contactless varactor‐loaded microstrip line embedded in the middle layer of the two stacked substrates of the MP antenna is constructed as a tuning structure so that the MP mode and the lower radiation null can be adjusted simultaneously. As a result, the fractional BW (FBW) of the filtering antenna can be reconfigured with a BW agility of 55.3% while the high selectivity is maintained. For demonstration, a prototype is implemented and tested. The simulated and measured results with good agreement are presented.

In this article, a half‐cut rectangular dense dielectric patch (DDP) with one grounded side plane is theoretically investigated for designing a compact low‐profile antenna. According to the properties and the E‐field distribution of the dominant TM101 mode, the half‐wavelength (λ/2) DDP can be bisected by effectively shorting the center plane to the ground, resulting in a miniaturized half‐cut λ/4 DDP. The size of the DDP is effectively reduced by 50% while maintaining the original resonant frequency of the dominant TM101 mode. The half‐cut λ/4 DDP can be well excited through aperture coupling for antenna design. The design procedure of the proposed antenna is given in detail. For demonstration, an antenna prototype centered at 4.15 GHz is implemented and measured. The simulated and measured results are given, showing good agreement.

A differential-fed dual-polarized dielectric patch (DP) antenna with high gain, wide bandwidth, and high isolation is investigated in this article. Based on the analysis of the anisotropic property of the DP antenna, further exploration of gain enhancement is carried out. The introduction of the square air hole in the substrate to obtain a hollow DP resonator is a crucial technique. It not only increases the electromagnetic radiation from the sidewalls of the DP resonator to further improve the gain to 8.9 dBi, but also shifts the dominant TM 101 mode upward to get close to the higher-order TM 121 mode to achieve bandwidth expansion of 19.4%. By using the differential-fed scheme to excite the TM 101 mode, TM 121 mode and their degenerate modes, dual-polarization operation and high isolation level can be obtained simultaneously. K E Y W O R D Sdielectric patch (DP) resonator, differential-fed, dual-polarized antenna, high gain, low-profile, wideband