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Mathematical Methods Of Statistics

Before the emergence of ultra-wideband (UWB) radios, widely used wireless communications were based on sinusoidal carriers, and impulse technologies were employed only in specific applications (e.g. radar). In 2002, the Federal Communication Commission (FCC) allowed unlicensed operation between 3.1–10.6 GHz for UWB communication, using a wideband signal format with a low EIRP level (−41.3dBm/MHz). UWB communication systems then emerged as an alternative to narrowband systems and significant effort in this area has been invested at the regulatory, commercial, and research levels.

IEEE Transactions on Microwave Theory and Techniques and Antennas and Propagation Announce a Joint Special Issue on Ultra-Wideband (UWB) Technology

This paper provides a systematic review of the mutual coupling in multiple-input multiple-output (MIMO) systems, including the effects on performances of MIMO systems and various decoupling techniques. The mutual coupling changes the antenna characteristics in an array, and therefore, degrades the system performance of the MIMO system and causes the spectral regrowth. Although the system performance can be partially improved by calibrating out the mutual coupling in the digital domain, it is more effective to use decoupling techniques (from the antenna point) to overcome the mutual coupling effects. Some popular decoupling techniques for MIMO systems (especially for massive MIMO base station antennas) are also presented.

/pdf/a-review-of-mutual-coupling-in-mimo-systems-557b1h0qhs.pdf

A Review of Mutual Coupling in MIMO Systems

Massive multiple-input multiple-output (M-MIMO) technology is considered to be a key enabling technology for future wireless communication systems. One of the challenges in effectively implementing an advanced precoding scheme to a large-scale array antenna is how to reduce the mutual coupling among antenna elements. In this paper, a new concept that is called array-antenna decoupling surface (ADS) for reducing the mutual coupling between antenna elements in a large-scale array antenna is proposed for the first time. An ADS is a thin surface that is composed of a plurality of electrical small metal patches and is placed in front of the array antenna. The partially diffracted waves from the ADS can be controlled to cancel the unwanted coupled waves. Two practical design examples are given to illustrate the design process and considerations, and to demonstrate the usefulness of ADS for the applications of phased array antennas and M-MIMO systems when commonly used precoding schemes are applied. The attractive features of ADS include its applicability to a large-scale array antenna; suitability for a wide range of antenna forms; wide decoupling bandwidth; and simplicity in implementation.

Array-Antenna Decoupling Surface

Nowadays synthetic aperture radar (SAR) and multiple-input-multiple-output (MIMO) antenna systems with the capability to radiate waves in more than one pattern and polarization are playing a key role in modern telecommunication and radar systems. This is possible with the use of antenna arrays as they offer advantages of high gain and beamforming capability, which can be utilized for controlling radiation pattern for electromagnetic (EM) interference immunity in wireless systems. However, with the growing demand for compact array antennas, the physical footprint of the arrays needs to be smaller and the consequent of this is severe degradation in the performance of the array resulting from strong mutual-coupling and crosstalk effects between adjacent radiating elements. This review presents a detailed systematic and theoretical study of various mutual-coupling suppression (decoupling) techniques with a strong focus on metamaterial (MTM) and metasurface (MTS) approaches. While the performance of systems employing antenna arrays can be enhanced by calibrating out the interferences digitally, however it is more efficient to apply decoupling techniques at the antenna itself. Previously various simple and cost-effective approaches have been demonstrated to effectively suppress unwanted mutual-coupling in arrays. Such techniques include the use of defected ground structure (DGS), parasitic or slot element, dielectric resonator antenna (DRA), complementary split-ring resonators (CSRR), decoupling networks, P.I.N or varactor diodes, electromagnetic bandgap (EBG) structures, etc. In this review, it is shown that the mutual-coupling reduction methods inspired By MTM and MTS concepts can provide a higher level of isolation between neighbouring radiating elements using easily realizable and cost-effective decoupling configurations that have negligible consequence on the array’s characteristics such as bandwidth, gain and radiation efficiency, and physical footprint.

/pdf/a-comprehensive-survey-on-various-decoupling-mechanisms-with-8ltuxavmy7.pdf

A Comprehensive Survey on “Various Decoupling Mechanisms With Focus on Metamaterial and Metasurface Principles Applicable to SAR and MIMO Antenna Systems”

This letter presents a dual-band inverted-F multiple-input-multiple-output (MIMO) antenna with improved isolation, covering the 2.4/5-GHz wireless local networks (WLAN) band. The proposed MIMO antenna is composed of two symmetrical winding inverted-F antenna elements. The two antenna elements are closely spaced with about 0.115 λ
 0
 of the lower band. The high isolation is achieved by building two decoupling devices, a meandering resonant branch and an inverted T-shaped slot etched on the ground for the higher band and the lower band, respectively. Furthermore, two U-shaped slits achieving better impedance matching are etched on the 50-Ω feeding lines to broaden the bandwidth of the high band. The impedance bandwidth (S
 11
 <; -10 dB) of the proposed antenna covers 2.4-2.48 GHz in the lower band and 5.15-5.825 GHz in the upper band, and the proposed configuration obtains 15-dB isolation within the 2.4- and 5-GHz WLAN bands, which shows a significant improvement compared to the initial design of the MIMO antenna. The simulation and measurement results indicate that the proposed inverted-F MIMO antenna system is quite suitable for WLAN applications.

A Dual-Band Inverted-F MIMO Antenna With Enhanced Isolation for WLAN Applications

In this communication, a metasurface-based decoupling method (MDM) is proposed to reduce the mutual couplings at two independent bands of two coupled multiple-input-multiple-output (MIMO) antennas. The metasurface superstrate is composed of pairs of non-uniform cut wires with two different lengths. It is compact in size and effective in decoupling two nearby dual-band patch antennas that are strongly coupled in the H-plane with the edge-to-edge spacing of only 0.008 wavelength at low-frequency band (LB). The antenna is fabricated and measured and the results show that the isolation between two dual-band antennas can be improved to more than 25 dB at both 2.5–2.7 GHz and 3.4–3.6 GHz bands, while their reflection coefficients remain to be below −10 dB after the metasurface superstrate is introduced. Moreover, the total efficiency is improved by about 15% in the low band and the envelope correlation coefficient (ECC) between the two antennas is reduced from 0.46 to 0.08 at 2.6 GHz and 0.08 to 0.01 at 3.5 GHz. The proposed method can find plenty of applications in dual-band MIMO and 5G communication systems.

Dual-Band Metasurface-Based Decoupling Method for Two Closely Packed Dual-Band Antennas

A new concept for decoupling two coupled antenna elements in a broad band using a coupled resonator decoupling network (CRDN) is proposed for the first time. A synthesis and design theory of a CRDN is presented. Based on the admittance parameters of a given antenna array, a set of required rational functions and, consequently, the coupling matrix for a second-order decoupling network is obtained analytically. To prove the concept, two prototypes using microstrip resonators are designed and experimentally studied. Measurement results have demonstrated that an isolation improvement of more than 10 dB can be achieved within more than 15% bandwidth in both examples. The benefits of using a CRDN for different levels of isolation in a MIMO terminal are investigated through experiments and simulations. The results have shown that, as compared to the existing decoupling scheme using a lumped element, the proposed CRDN scheme can significantly increase the radiation efficiency, reduce the correlation, improve the channel capacity, and above all enhance the throughput of a MIMO terminal. The technique is general and can be applied to both symmetric and asymmetric arrays.

https://www.ee.cuhk.edu.hk/~klwu/pdf/ap201405.pdf

A Coupled Resonator Decoupling Network for Two-Element Compact Antenna Arrays in Mobile Terminals

A new decoupling scheme called dual-band coupled resonator decoupling network (CRDN) is presented. By properly designing the coupling coefficients between two pairs of coupled resonators, the network can effectively reduce the mutual couplings between two coupled dual-band antennas in two bands simultaneously. The new scheme is proved by a practical microstrip version of the device for two dual-band antennas working at 2.4 and 5.2 GHz frequency bands. A compact planar dual-band CRDN consisting of a pair of dual-band open-loop square ring resonators is proposed. The measured scattering parameters of two coupled antennas with and without the dual-band CRDN in free space (FS) and with hand phantom demonstrate that the isolation between the two antennas in both the low and high bands can be improved from 8 to 10 dB, respectively, to below 20 dB while maintaining a good matching performance. The total efficiency and envelop correlation coefficient for the decoupled antennas show a significant improvement as compared to the coupled antenna case. The proposed dual-band CRDN scheme is easy to be implemented in an integrated device, and is very attractive for practical multiple input and multiple output (MIMO) applications.

https://www.ee.cuhk.edu.hk/~klwu/pdf/ap201507.pdf

A Dual-Band Coupled Resonator Decoupling Network for Two Coupled Antennas

In this paper, an antenna interference cancellation chip (AICC) with a high-pass response is proposed to mitigate the mutual coupling of two antennas resonating in contiguous frequency bands. Using the most up-to-date low temperature co-fired ceramic (LTCC) technology, the chip only occupies a compact volume of $1.6\times 0.8\times 0.6$ mm3. Two external tuning capacitors and two shunt inductors together with the LTCC AICC device which are in shunt with two coupled antennas, are able to improve the antenna isolation near band-edge by more than 15 dB without sacrificing antenna performance in its useful resonating bands. The high-pass property of the AICC device prevents the decoupling design near 2.4GHz affecting the successful operation of GPS at 1.575 GHz. The superiority of the proposed method is verified with active measurement of a Mi-Fi (mobile Wi-Fi) device in Wi-Fi hotspot mode using the AICC device. The proposed AICC device and corresponding decoupling method with the device can find plenty of applications in long-term-evolution and future 5G wireless platforms.

http://ir.nssc.ac.cn/bitstream/122/6366/1/2018638097-38105.pdf

Luyu Zhao

Papers

A Dual-Band Inverted-F MIMO Antenna With Enhanced Isolation for WLAN Applications

Dual-Band Metasurface-Based Decoupling Method for Two Closely Packed Dual-Band Antennas

A Coupled Resonator Decoupling Network for Two-Element Compact Antenna Arrays in Mobile Terminals

A Dual-Band Coupled Resonator Decoupling Network for Two Coupled Antennas

A High-Pass Antenna Interference Cancellation Chip for Mutual Coupling Reduction of Antennas in Contiguous Frequency Bands