In this paper, a novel in-band and out-of-band low radar cross-section (RCS) circularly polarized (CP) antenna array based on a hybrid mechanism of absorption and phase cancellation is proposed. The antenna scattering-reduction unit is a frequency-selective absorber-polarization converter (FSAPC) unit comprising a resistive metasurface (RM) unit, four frequency-selective surface (FSS) units, and four polarization-conversion metasurface (PCM) units arranged in cascade. The RM employs a parallel resonant structure comprising metal rings and parallel lines to create an in-band transmission window for the radiation while absorbing the out-of-band electromagnetic waves. The modified PCM configuration is arranged along the diagonal with cutting round-arcs and serves two distinct functions. Firstly, it converts the co-polarized component of in-band incidence into a cross-polarized one. Secondly, the antenna radiated wave is converted from linear to circular polarization through the decomposition of the electric field by the metal square. In order to verify the functional properties of the FSAPC structure, the properties of the constituent units and the FSAPC unit are elucidated and investigated in two dimensions: field and circuit, which is done based on the principles of double-port equivalent circuit and coupler theory. Furthermore, the slot antenna array is directly integrated with the metal reflector of the FSAPC in a chessboard configuration, thereby enabling the realization of the desired radiation performance. The simulation and measurement results demonstrate that the FSAPC-based antenna array is capable of achieving good left-handed CP radiation characteristics, and also adept at reducing the RCS by over 10 dB across the 5.73 GHz to 17.5 GHz range. The results demonstrate that the antenna array is capable of simultaneously achieving both stealth and radiation functions, rendering it an apt candidate for integration into modern weapon platforms.

An ultra-wideband (UWB) multiple-input, multiple-output (MIMO) antenna with a reasonably compact size of 30 × 18 × 1.6 mm³ is presented in this paper. The proposed antenna contains two radiating components, each of which is made up of three elliptically shaped patches situated 60 degrees apart, and resembles the shape of a flower. Moreover, the proposed antenna design incorporates a T-like ground branch that functions as a decoupling structure, and is composed of two modified inverted-L branches and an I-shaped stub, offering an isolation of more than 20 dB over the whole operation band (4.3–15.63 GHz). Furthermore, the proposed antenna system was fabricated and tested, and the envelope correlation coefficient (ECC), diversity gain (DG), and total active reflection coefficient (TARC), as well as the radiation characteristics and MIMO performance, were analyzed. The proposed UWB-MIMO antenna may be a suitable candidate for diverse UWB applications, based on the simulated and measured results of this study.

This article presents an ultra-wideband (UWB) monopole antenna with triple band notch characteristics. The proposed antenna consists of an octagonal patch, fed with a 50 Ω line, which occupies a compact size of 40 mm × 29 mm (0.36λ × 0.26λ, λ is computed using 2.7 GHz frequency) and resonances at a relatively low frequency (2.94 GHz). Specifically, an L-shaped stub, an inverted C-shaped slot, and a pair of U-shaped resonating structures are introduced into the design, which allow antenna to generate three band notches at 3.22–3.83 GHz, 4.49–5.05 GHz and 7.49–8.02 GHz, corresponding to WiMAX band, Indian national satellite (INSAT) band, and X-band satellite frequencies, respectively. In the center of the notched band, the antenna has lower efficiency and gain, essentially indicating that the antenna has good interference rejection performance. To evaluate its performance, the proposed antenna has been fabricated and measured, and the relevant functional parameters, such as S-parameters, voltage standing wave ratio (VSWR) and radiation property, have been studied.

To satisfy the demand for 5G communication to smartphone terminal antennas in element quantity and isolation, an eight-element wideband MIMO antenna set of high isolation level is proposed. Each antenna element in the array is a double-L antenna consisting of an L-shaped slot and an L-shaped 50 Ω microstrip line. The L slot is formed by adding an I-shaped open circuit directly to the side of the rectangular slot. In addition, the antenna arrays are located on the long bezels on both sides of the mobile phone motherboard, and the coupling feed is made in the frequency range of 3.6–4.7 GHz through the L-shaped microstrip line, so as to cover the 5G NR band (N77/N78/N79). Finally, the four element pairs (8 components) achieve isolation of greater than 11 dB, the performance frequency range is 3.6–4.7GHz, the return loss is −6 dB, the total efficiency is greater than 85%, and the envelope correlation coefficient is less than 0.08. Other MIMO performances are also calculated, the design process is discussed in detail, and one-handed grip mode and two-handed grip mode are discussed to demonstrate their stabilities in real-world applications.

This letter proposes a broadband reconfigurable antenna capable of forming single and dual beam radiation, with switchable polarization states. The antenna consists of a reconfigurable power divider and a 2×2 magnetoelectric (ME) dipole antenna array. The two ports of the antenna units operate independently to achieve mutually orthogonal dual-polarization characteristics. A grounded thin copper column is placed between adjacent antenna units to enhance the operating bandwidth and reduce coupling between units. To achieve stable dual beam radiation, a wideband phase shift branch is added into the design of the power divider to ensure a stable 180° phase difference in the range of 3.5-6 GHz. Additionally, by embedding diodes into the power divider to control the switching between different states, different antenna units can be activated to achieve polarization conversion and switching between single and dual beams. The switching of antenna working state is controlled by an external micro-control system to ensure stable and rapid switching between beam states. The experimental and simulation results are in good agreement, and it can be seen that the antenna operates in the range of 3.52-6 GHz with four polarization modes and eight beam states. As an application, this antenna is highly suitable for complex communication scenarios.

A compact, multiband two-port MIMO antenna is proposed in this paper for various wireless transmission networks, where the overall size of the antenna is only 30 × 20 × 1.6 mm3. The proposed MIMO antenna consists of two radiating patches, each of which comprises a semicircle and a semi-regular hexagon, as well as the surface-etched C-slot and U-slot to tailor the antenna’s return loss characteristics. In proposed antenna, a parasitic branch forms when the ground plane’s meandering branches are symmetrically distributed. On one hand, it can increase the ground plane’s effective area and enhance the antenna’s return loss characteristics. A neutralization line, on the other hand, is generated, thereby limiting the current transmission on the ground plane. A cross-shaped slit in the ground’s center is also employed to further promote isolation between the radiation elements. According to obtained results, the antenna can cover the frequency bands 0.67-7.29 GHz, 8.07-12.11 GHz, 14.07-15.41 GHz, and 16.04-22 GHz (S11<−10 dB). Moreover, an RF isolation larger than 18 dB exists between the two ports. Lastly, in terms of ECC, DG, TARC, CCL, and MEG, the diversity performances are all satisfactory.