A wideband neutralization line is proposed to reduce the mutual coupling of a compact ultrawideband (UWB) 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 mm × 16 mm is achieved. The designed UWB MIMO antenna is fabricated. S parameters, radiation patterns, total efficiency and realized gain of the prototype are measured and compared with the simulations. Index Terms-MIMO, UWB antenna, mutual coupling 1536-1225 (c)

In analogy with the established discipline of room acoustics various aspects of diffuse wideband microwave propagation in a room are treated. It is shown that an equivalent to Sabine's equation for reverberation time in a room is valid for the completely diffused field, depending only on the volume, the surface area and an effective absorption coefficient. An exponential decay of the power versus delay is a consequence of the assumptions. Furthermore, the concept of a reverberation distance is also valid. This is the distance from a transmit antenna where the received diffuse, randomly scattered power equals the direct line-of-sight received power, such that the diffuse power dominates for distances larger than the reverberation distance. A number of measurements in a large room support the theory with an effective absorption coefficient of 0.5. The power delay profiles around the room from a transmitter in the ceiling vary only in the first arriving part of the impulse, whereas the tail being dominated by the diffuse field has the same power level for a given delay and the same decay rate all over the room. It is also a consequence of the theory that the incident diffuse fields on an antenna are uniformly distributed in angle. λ −))) 4ΙςΩΣΡΕΠ ΨΩΙ Σϑ ΞΛΜΩ ΘΕΞΙςΜΕΠ ΜΩ ΤΙςΘΜΞΞΙΗ 4ΙςΘΜΩΩΜΣΡ ϑςΣΘ −))) ΘΨΩΞ ΦΙ ΣΦΞΕΜΡΙΗ ϑΣς ΕΠΠ ΣΞΛΙς ΨΩΙΩ ΜΡ ΕΡ] ΓΨςςΙΡΞ Σς ϑΨΞΨςΙ ΘΙΗΜΕ ΜΡΓΠΨΗΜΡΚ ςΙΤςΜΡΞΜΡΚ ςΙΤΨΦΠΜΩΛΜΡΚ ΞΛΜΩ ΘΕΞΙςΜΕΠ ϑΣς ΕΗΖΙςΞΜΩΜΡΚ Σς ΤςΣΘΣΞΜΣΡΕΠ ΤΨςΤΣΩΙΩ ΓςΙΕΞΜΡΚ ΡΙ[ ΓΣΠΠΙΓΞΜΖΙ [ΣςΟΩ ϑΣς ςΙΩΕΠΙ Σς ςΙΗΜΩΞςΜΦΨΞΜΣΡ ΞΣ ΩΙςΖΙςΩ Σς ΠΜΩΞΩ Σς ςΙΨΩΙ Σϑ ΕΡ] ΓΣΤ]ςΜΚΛΞΙΗ ΓΣΘΤΣΡΙΡΞ Σϑ ΞΛΜΩ [ΣςΟ ΜΡ ΣΞΛΙς [ΣςΟΩ 4ΨΦΠΜΩΛΙΗ ΜΡ −))) %ΡΞΙΡΡΕΩ ΕΡΗ 4ςΣΤΕΚΕΞΜΣΡ 1ΕΚΕ⊥ΜΡΙ :ΣΠ 2Σ Τ ¥ %ΤςΜΠ (3− 1%4

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A transmission-line-based decoupling technique for dual-polarized multiple-input and multiple-output (MIMO)antenna arrays is presented and analyzed. The proposed scheme enables well-canceled coupling for the adjacent elements under co-polarization, without degrading the isolation of the cross-polarized ports. Firstly, a decoupling network based on the presented method for a 2×2 MIMO array is provided, along with a comprehensive design procedure. Calculations and simulations are operated to verify the decoupling performance. For further verification, a 2×2 dual-polarized patch array with the proposed decoupling method is developed. The decoupling network characterizes low profile, compact size, and low insertion loss, which is realized in a single layer. Measurements denote that the isolations between the co-polarized elements are improved from 16-20 dB to over 30 dB after decoupling at the center frequency of 2.45 GHz. Subsequently, based on the proposed 2×2 decoupling method, a decoupling network for large-scale dual-polarized MIMO arrays is presented. A design example of a 4×4 dual-polarized patch antenna array is established. Full-wave simulations indicate that the isolations are enhanced to better than 30 dB with a small insertion loss of less than 0.45 dB, and can widely be used for phased array and massive MIMO array systems.

Accurate characterization of spatial multipath channels at millimeter wave bands has gained significant interest both in industry and academia. A channel measurement was conducted at three different frequency bands, i.e., 2 − 4, 14 − 16, and 28 − 30 GHz in a line-of-sight (LOS) and an obstructed-LOS (O-LOS) scenarios in an empty room environment. A vector network analyzer connected to a virtual uniform circular array and to a rotational directional horn antenna was used in the measurements, respectively. Angle-of-arrivals and delay-of-arrivals of the multipath components were obtained from the measurements for the three frequency bands. Room electromagnetic properties for the three different frequencies at different propagation scenarios were investigated as well.