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
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 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.

Mutual Coupling Reduction for UWB MIMO Antennas with a Wideband Neutralization Line

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.

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A Review of Mutual Coupling in MIMO Systems

A compact multiple-input-multiple-output (MIMO) antenna is presented for ultrawideband (UWB) applications. The antenna consists of two open L-shaped slot (LS) antenna elements and a narrow slot on the ground plane. The antenna elements are placed perpendicularly to each other to obtain high isolation, and the narrow slot is added to reduce the mutual coupling of antenna elements in the low frequency band (3-4.5 GHz). The proposed MIMO antenna has a compact size of 32 ×32 mm
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, and the antenna prototype is fabricated and measured. The measured results show that the proposed antenna design achieves an impedance bandwidth of larger than 3.1-10.6 GHz, low mutual coupling of less than 15 dB, and a low envelope correlation coefficient of better than 0.02 across the frequency band, which are suitable for portable UWB applications.

Compact Printed MIMO Antenna for UWB Applications

A compact, high performance, and novel-shaped ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with low mutual coupling is presented in this paper. The proposed antenna consists of two radiating elements with shared ground plane having an area of $50\times 30$ mm2. F-shaped stubs are introduced in the shared ground plane of the proposed antenna to produce high isolation between the MIMO antenna elements. The designed MIMO antenna has very low mutual coupling of (S21 7.4 dB), high multiplexing efficiency ( ${\eta }_{\mathrm {Mux}}> -3.5$ ), and high peak gain over the entire UWB frequencies. The antenna performance is studied in terms of S-Parameters, radiation properties, peak gain, diversity gain, envelop correlation coefficient, and multiplexing efficiency. A good agreement between the simulated and measured results is observed.

Mutual Coupling Reduction Using F-Shaped Stubs in UWB-MIMO Antenna

This communication presents a bandwidth-enhanced, compact, monopole antenna with modified ground plane for modern automotive ultra wide-band (UWB) applications The proposed antenna has hybrid geometry and is constructed using half circular ring and half square ring The ground plane of the fundamental radiator is curved and defected to improve the VSWR bandwidth An extended ground stub is added to further enhance the bandwidth to suit the modern automotive requirements The designed antenna covers 31–109 GHz frequency spectrum with ${\mathrm {VSWR}} \leq {2}$  This antenna can be conveniently placed inside the shark fin housing or it can be printed along with the existing print circuit board (PCB) electronics nullifying the need for dedicated location for in-car communications Furthermore, a simple two-port multiple input multiple output (MIMO) antenna is constructed and its diversity performance is estimated The prototype is fabricated and tested for impedance and radiation characteristics

Compact UWB Monopole Antenna for Automotive Communications

A compact multiple-input-multiple-output (MIMO) antenna with a small size of 26×40 mm2 is proposed for portable ultrawideband (UWB) applications. The antenna consists of two planar-monopole (PM) antenna elements with microstrip-fed printed on one side of the substrate and placed perpendicularly to each other to achieve good isolation. To enhance isolation and increase impedance bandwidth, two long protruding ground stubs are added to the ground plane on the other side and a short ground strip is used to connect the ground planes of the two PMs together to form a common ground. Simulation and measurement are used to study the antenna performance in terms of reflection coefficients at the two input ports, coupling between the two input ports, radiation pattern, realized peak gain, efficiency and envelope correlation coefficient for pattern diversity. Results show that the MIMO antenna has an impedance bandwidth of larger than 3.1-10.6 GHz, low mutual coupling of less than -15 dB, and a low envelope correlation coefficient of less than 0.2 across the frequency band, making it a good candidate for portable UWB applications.

Compact MIMO Antenna for Portable Devices in UWB Applications

A multiple-input-multiple-output (MIMO) band-notched antenna with a compact size of only $22 \times 36\;\mathrm{mm}^2 $ is proposed for portable ultrawideband (UWB) applications. The antenna consists of two square monopole-antenna elements, a T-shaped ground stub, a vertical slot cut on the T-shaped ground stub to reduce mutual coupling, and two strips on the ground plane to create a notched frequency band. Simulation and measurement are used to study the antenna performance in terms of impedance matching, isolation between the two input ports, radiation pattern, efficiency, peak gain, and envelope correlation coefficient. Results show that the antenna can operate from 3.1 to more than 11 GHz with a notched band in 5.15–5.85 GHz. In the center notched frequency, the efficiency drops to 7%, indicating a good interference suppression performance. The mutual coupling is less than $- 15\;\mathrm{dB}$ and the envelope correlation coefficient is less than 0.1. The performances of the MIMO antenna when installed on a PCB with a standard size, with an USB connector and device housing, are also studied. Results show that the proposed MIMO antenna is a good candidate for portable UWB applications.

Compact MIMO Antenna for Portable UWB Applications With Band-Notched Characteristic

This paper presents a dual-band planar antenna with a compact radiator for 24/52/58-GHz wireless local area network (WLAN) applications The antenna consists of an L-shaped and -shaped radiating elements to generate two resonant modes for dual-band operation The -element fed directly by a 50-Ω microstrip line is designed to generate a frequency band at around 55 GHz to cover the two higher bands of the WLAN system (using the IEEE 80211a standard) The L-element is coupled-fed through the L-element and designed to generate a frequency band at 244 GHz to cover the lower band of the WLAN system (using the 80211 b/g standards) As a result, the L- and E-elements together are very compact with a total area of only 8 × 113 mm2 Parametric study on the key dimensions is investigated using computer simulation For verification of simulation results, the antenna is fabricated on a 40 × 30 × 08 mm3 substrate and measured The effects of the feeding cable used in the measurement system and the housing and liquid crystal display of wireless devices on the return loss, radiation pattern, gain and efficiency are also investigated by computer simulation and measurement

Dual-Band Antenna With Compact Radiator for 2.4/5.2/5.8 GHz WLAN Applications

In this paper, the design of a novel chipless ultra-wideband radio-frequency identification (UWB RFID) system is proposed. The system employs printable uniplanar chipless tags and a pair of high-gain reader antennas. The chipless tag is composed of two UWB monopole antennas, connected by a coplanar waveguide (CPW). The tag's ID is represented by a spectral signature in the UWB frequency range, and is created by a multi-resonator embedded on the coplanar waveguide. The detection of the tag's ID is based on using only the amplitude of the spectral signature, which significantly simplifies the complexity of detection. The reader employs two separate Vivaldi antennas - one for transmitting a vertically polarized signal, and the other for receiving a horizontally polarized signal - to reduce the mutual coupling between the uplink and downlink signals. Further reduction of mutual coupling is achieved by using a copper plate at the reader to separate the uplink and downlink signals. These two proposed methods together reduced the mutual coupling by 20 dB. The chipless RFID tag with eight coplanar waveguide resonators in a group and the reader antennas were designed using computer simulation, and fabricated on Rogers substrates for measurement. The results of studies in an anechoic chamber showed that the proposed UWB RFID system could achieve a reading range of larger than 30 cm, at least three times longer than the maximum distance of a similar system reported by others. This indicated that the proposed system has great potential for short-range item tracking at low cost.

Design of Chipless UWB RFID System Using A CPW Multi-Resonator

A multiband MIMO antenna using planar technology is proposed for next generation mobile communication system. The antenna consists of two symmetrical monopole elements printed in parallel to each other at the upper and lower corners of a printed-circuit board (PCB) with a size 50×110 mm2 which is similar to the side of a mobile phone. The two monopoles have two branch strips to generate two frequency bands. By using a parasitic element in each monopole, a much enhanced bandwidth in the upper band can be obtained. A lumped-impedance network is designed to enhance matching at the input ports for the two antenna elements. Computer simulation is used to study, design and optimize the antenna. Results indicate that the proposed MIMO antenna has a very bandwidth enough to cover the LTE (lower band), DCS1800, PCS1900, UMTS-2100, Wibro Band, 2.4G-WLAN, and Wimax (upper band) systems. To enhance the isolation between the two monopole elements within the desirable frequency bands, a slit is cut in the middle on the PCB ground. The MIMO antenna a very low profile and low cost which makes the design very attractive for mobile phone applications.

Li Liu

Papers

Compact MIMO Antenna for Portable Devices in UWB Applications

Compact MIMO Antenna for Portable UWB Applications With Band-Notched Characteristic

Dual-Band Antenna With Compact Radiator for 2.4/5.2/5.8 GHz WLAN Applications

Design of Chipless UWB RFID System Using A CPW Multi-Resonator

Design of a printed multiband MIMO antenna