MIMO systems introduce more than one antenna at the transmitting and receiving ends.
Isolation between antenna elements is a critical parameter and an important requirement of MIMO systems.
Maintaining an inter-element spacing above half of the free-space wavelength is a good antenna isolation technique in MIMO systems with fewer antenna elements.
Antenna isolation is critical for achieving excellent MIMO system performance
For the high bit rate transmission that is required to support multimedia services, modern wireless communication systems rely on multi-input-multi-output systems (MIMO). MIMO antenna systems are a promising solution to high data rate requirements; they offer increased channel capacity with high spectrum efficiency, without any additional transmitted power or bandwidth requirements. Since MIMO systems use two or more antennas on both transmitting and receiving ends, antenna isolation is critical for achieving excellent antenna performance. In this article, we will discuss MIMO antenna systems and the importance of antenna isolation.
MIMO vs. SISO
With technological advancements, there is a need for enhanced bandwidth capabilities, high data rates, and an increased number of channels. Unfortunately, single-input, single-output (SISO) antenna systems fail to meet these system requirements. With the establishment of 3G, 4G, and 5G networks, MIMO technology is considered the future of antenna technology. The emergence of wireless standards such as IEEE 802.11n, IEEE 802.11ax WiFI variants, and mobile WiMax systems have also led to the extensive application of MIMO systems in the communication field.
MIMO Antenna Technology
High-end systems demand the use of multiple-input, multiple-output technology in antennas. MIMO systems enable wireless communication transceivers to handle multiple antennas simultaneously. MIMO architecture employs numerous antennas and multiple paths by introducing more than one antenna at the transmitting and receiving ends to improve transmission capacity.
In MIMO antenna technology, different sets of data symbols are used for transmission, which helps achieve high data rates compared to SISO systems. At the receiving end, data is processed using mathematical algorithms to retrieve the original information transmitted. Even though MIMO technology requires complex processing and switching to control each antenna in the system, most modern wireless application systems are based on them due to the advantages of high data throughput with good bit-error rates (BER). The data rate is maintained at a high level even under the influence of interference, multipath fading, and signal fading. Introducing multiple variants of the same signal to reach a destination mitigates fading issues, increasing the signal-to-noise ratio (SNR) and BER.
One of the main highlights of MIMO systems is the expansion of bandwidth within a given spectral bandwidth and space. MIMO systems offer this benefit by enabling spatial channelization and time, frequency, and space diversity. Considering these advantages, MIMO antenna systems are the best technology for wireless communication systems that require a stable connection with less congestion.
We will briefly summarize the advantages of MIMO systems in the upcoming section.
Advantages of MIMO Antenna Technology
- High downlink and uplink throughput
- High-quality communication service with increased spectral efficiency
- Reduced BER and increased SNR
- Low risk of tapping and high data security
- Time, frequency, and space diversity techniques minimize signal fading effects
- Employing other technologies such as beamforming and space-time block coding extends the coverage area or range of the system
Antenna Isolation in MIMO Systems
Isolation between antenna elements is a critical parameter and an important requirement for MIMO systems. In powerful MIMO antenna systems, antenna isolation refers to poor mutual coupling between antenna elements. With a decreasing form factor of portable devices, achieving good isolation between closely packed antenna elements is a hurdle in MIMO system design. Various antenna isolation techniques are employed in MIMO systems for enhanced channel bandwidth and minimized radiation pattern degradation.
The antennas in MIMO systems should be isolated from each other to ensure an effective and efficient MIMO system. Maintaining an inter-element spacing above half of the free-space wavelength is a good antenna isolation technique when the number of antenna elements is lower. With an increasing number of antenna elements, employing 2 spacing becomes difficult and leads to the degradation of MIMO system capacity and performance.
Some other antenna isolation techniques in MIMO systems are:
- Defected ground structure - In this antenna isolation technique, the ground plane structure is modified to provide a band-stop effect that prevents the flow of ground currents between antenna elements.
- Decoupling network - Antenna isolation can be achieved by decoupling antenna elements. Decoupling networks establishes negative coupling, thus decoupling adjacent antenna elements.
- Using parasitic elements - The introduction of parasitic elements between the antennas terminates the coupled field current flow between the antenna elements, producing a negative coupling field and minimizing the total coupling on the target antenna.
Using neutralization lines, metamaterials, and electromagnetic bandgap structures are some of the other antenna isolation techniques that can be employed to enhance MIMO system performance. With Cadence software, you can design effective and efficient MIMO systems with clear antenna isolation. The layout and simulation tools in Cadence software helps you to isolate antennas sufficiently to achieve enhanced channel bandwidth and improved data rates in MIMO systems.
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