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In this paper, we presented an ultra-wideband multiple-input multiple-output (MIMO) antenna system with high element-isolation for the application in 5G metal-frame smartphones. We proposed T-shaped and C-shaped slots on the metal frame generating four resonances to enhance the bandwidth. What’s more, we introduce modified H-shaped slots between each antenna-element to improve the element-isolation of MIMO antenna system. As a result, the MIMO antenna system has a wide bandwidth of 58% ranging from 3.3 to 6 GHz and the element-isolation is over 18 dB crossing the effective frequency band. Thanks to the decent element-isolation, the envelope correlation coefficient (ECC) between each antenna-element is below 0.05 providing a reliable anti-interference for the MIMO antenna system. In addition, the measured radiation efficiencies of the MIMO antenna system are higher than 40%. At last, we analyze the effects caused by user’s hands and head to guarantee the robustness of the MIMO antenna system in practical applications.

This paper proposes a variable thickness radome for application in millimeter-wave (mm-wave) radar at missile warhead, so as to figure out the radiation distortion caused by uniform thickness radome (UTR). By choosing a appropriate condition of wall thickness of radome, the adverse effect of field reflection and phase delay on radiation pattern is minimized. Moreover, the radome thickness is further optimized through simulation, by which the ripple variation of main beam is effectively mitigated and radiation pattern become more symmetric. Simulated results show that the radiation performance of the 24-GHz off-center antenna array with our proposed radome has been improved a lot in terms of beam symmetry and broadside gain level.

A differentially-fed circular patch antenna under dual high-order modes for enhanced bandwidth and stable high gain is proposed in this paper. The current distribution of TM 31 mode is reconstructed by loading two open slots at the edge of patch, by which the broadside radiation of TM 31 mode is substantially increased. By loading an additional slot in patch’s center, the current of TM 12 mode is reshaped to be more in-phase, and so the sidelobe radiation is dramatically reduced. The resonant frequencies of TM 31 and TM 12 modes are then reallocated and get close to each other due to the loading of slots and shorting pins, which finally contributes to an enhanced bandwidth of 12.9%. Moreover, the antenna produces high gain up to 13.7 dBi, while the beamwidth and gain level are kept stable in band.

A resonator feeding method is proposed in this paper to enhance the bandwidth and suppress the adjacent modes of a square patch antenna under operation of TM03 mode. The radiating patch is loaded with three slots for sidelobe reduction, and it is coupled to a half-wavelength resonator beneath, which is fed by a probe. On the one hand, the feeding resonator helps to generate an additional resonant mode, and thus widens the operating bandwidth. On the other hand, the feeding structure can effectively suppress the adjacent TM 20 , TM 21 , TM 22 and TM 23 modes, and this can contribute to more selective and stable gain performance. The simulated results show that a maximum gain of 14.3 dBi has been realized and the bandwidth is broadened from 1.8% to 3.6%.

In this paper, a high-performance radome for millimeter wave (mm-Wave) antenna applications is proposed. Firstly, a microstrip patch antenna operating at 24 GHz is designed. A conventional radome is subsequently mounted on the patch antenna so as to protect the antenna from damage. However, since the wavelength of mm-Wave antenna is similar to the thickness of the radome, it would result in distortion of radiation patterns and reduction of radiation directivity. In order to overcome this problem, a novel and high performance radome is investigated by stacking six pieces of substrates in the traditional radome. In this way, the directivity is about 7 dBi higher than that of the antenna without the radome.

In this paper, a new design of a differential-fed microstrip patch antenna (MPA) with dual-band high gain is proposed under the operation of TM 01 and TM 03 resonant modes. Initially, three transverse slots are etched along the central line of the patch to interrupt the out-of-phase current of TM 03 mode on the surface. Subsequently, by symmetrically introducing a set of shorting pins, the resonant frequency of TM 01 mode is progressively turned up, and the radiation gain is hence effectively enhanced due to the enlarged patch size with respect to the operating wavelength. In addition, the antenna can be well matched in the desired 3.6 GHz and 5.9 GHz wireless communication network bands by properly adjusting the shorting positions of pins and length of slots. The simulated results demonstrate that at least 10 dBi realized gain can be obtained in both the lower and upper bands, and the radiation patterns in the two bands show agreeable beamwidths, while keeping antenna profile as low as 0.024 free-space wavelength.

In this paper, the slot loading effect on the TM 03 mode high-gain square patch antenna is investigated in terms of its impedance and radiation performance. Three different slot configurations along the central line of the patch can all reduce sidelobes in the E-plane. However, the H-plane beamwidth, impedance bandwidth and radiation Q factor in these cases are significantly different. Initially, the central slot loading can help to achieve broader H-plane beamwidth, lower Q factor and the wider impedance bandwidth. In contrast, narrower H-plane beamwidth, higher Q factor and the narrower impedance bandwidth will be obtained by etching the slots at two edges. Consequently, more balanced performance can be obtained by loading both the central and sided slots.