A wideband neutralization line is proposed to reduce the mutual coupling of a compact ultrawideband (UWB) multiple-input-multiple-output (MIMO) antenna. With the introduced decoupling method, the designed UWB MIMO antenna covers the band of 3.1-5 GHz with an isolation of higher than 22 dB. The proposed wideband neutralization line is not necessarily placed in the clearance area between two MIMO elements and can be put above the copper ground. A small clearance (antenna area) of 35 ×16 mm ² is achieved. The designed UWB MIMO antenna is fabricated. Sparameters, radiation patterns, total efficiency, and realized gain of the prototype are measured and compared to the simulations.

This letter proposes a new design of millimeter-wave (mm-Wave) array antenna package with beam steering characteristic for the fifth-generation (5G) mobile applications. In order to achieve a broad three-dimensional scanning coverage of the space with high-gain beams, three identical subarrays of patch antennas have been compactly arranged along the edge region of the mobile phone printed circuit board (PCB) to form the antenna package. By switching the feeding to one of the subarrays, the desired direction of coverage can be achieved. The proposed design has >10-dB gain in the upper spherical space, good directivity, and efficiency, which is suitable for 5G mobile communications. In addition, the impact of the user's hand on the antenna performance has been investigated.

Massive MIMO is envisioned as a promising technology in 5G and beyond 5G communication. Channel models are of great importance for the development and performance assessment of massive MIMO systems. Since massive MIMO systems are equipped with large-aperture antenna arrays, antenna elements at different spatial positions would observe different channel multipath characteristics, which is so-called spatial non-stationarity (SnS). The SnS property of multipaths has been observed in many reported massive MIMO channel measurements. However, characterization and explanations of SnS have not been adequate in existing statistical channel modeling, and deterministic models (e.g., Ray-tracing) are difficult to implement due to the high complexity. This paper proposes a realistic yet low-complexity SnS channel modeling framework for massive MIMO systems and its validation based on both channel measurements and Ray-tracing simulations. In this work, we firstly perform an 6 GHz-bandwidth millimeter-wave (mmWave) indoor channel measurement campaign with a 0.5 m-radius virtual uniform circular array (UCA), where the SnS phenomena are clearly observed. Then, we propose the massive MIMO channel modeling framework that captures the observed SnS property from physical propagation mechanisms of dominant multipaths in mmWave channels, i.e., blockage, reflection, and diffraction. Compared to traditional stationary channel modeling, only one extra parameter accounting for SnS has been added in the proposed framework, which is desirable for its low-complexity implementation. Finally, the proposed framework is validated with site-specific Ray-tracing simulations. The SnS phenomena observed in the measurements are reproduced well in the modeling results according to the proposed framework, and high similarities between the target channels and modeling results are achieved. The proposed framework is valuable for the development of massive MIMO systems, since it is realistic, low-complexity, and accurate.

In this paper, a recently conducted measurement campaign for unmanned-aerial-vehicle (UAV) channels is introduced. The downlink signals of an in-service long-time-evolution (LTE) network which is deployed in a suburban scenario were acquired. Five horizontal and five vertical flight routes were considered. The channel impulse responses (CIRs) are extracted from the received data by exploiting the cell specific signals (CRSs). Based on the CIRs, the parameters of multipath components (MPCs) are estimated by using a high-resolution algorithm derived according to the space-alternating generalized expectation-maximization (SAGE) principle. Based on the SAGE results, channel characteristics including the path loss, shadow fading, fast fading, delay spread and Doppler frequency spread are thoroughly investigated for different heights and horizontal distances, which constitute a stochastic model.

In this communication, a dual-band shared aperture antenna is presented. The proposed antenna achieves dual-band operation by housing both a low-frequency patch antenna array and a high-frequency reflectarray in the same aperture area. The two different antenna types are combined into a single-antenna product without any significant performance loss. The antenna has a layered structure that allows the low-frequency antenna array to have both a sufficient impedance bandwidth and realized gain. The antenna has a shared aperture since the high-frequency reflectarray has unit elements within the area of the low-frequency patch antenna array. This allows the antenna to achieve a good realized gain in the high-frequency band. The proposed antenna is fabricated and measured. The prototype is designed for S- and Ka-bands resulting in a frequency ratio of 7.37. The shared aperture size is 156 mm $\times156$ mm $\times4.624$ mm ( $1.82\lambda \times 1.82\lambda \times 0.05\lambda $ at S-band and $13.4\lambda \times 13.4\lambda \times 0.40\lambda $ at Ka-band). Measurements show the impedance bandwidth to be 200 MHz (6%) and 5.1 GHz (20%) and the peak realized gain to be 13.70 and 27.65 dBi at 3.5 and 25.8 GHz, respectively. A very good agreement between the simulated and measured results is observed.