Original In-depth: Avoiding Connector Reflections in Millimeter-Wave Applications
Latest update time：2019-10-09
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5G opens up new horizons
随着新一代蜂窝通信5G的发展势头日渐增强，部署5G通信基础设施的竞争也开始如火如荼地进行。移动运营商们正忙于部署基础设施，并启动营销计划，以吸引大家升级自己的智能手机服务合同与手机配置，从而充分利用5G显著提高的数据速率。与上一代3G向4G的转变不同，5G的通信架构不是一次迭代升级。5G首次使用了24至40GHz毫米波（
mmWave
）频谱中的频率，另外还与已许可和未许可sub-6GHz频段中的多射频通信网络共存。
Using mmWave for 5G
To achieve the dramatic increase in data speeds that 5G will deliver (expected to be at least four times faster than 4G), it will require the use of high-bandwidth millimeter wave spectrum. But using such high frequencies presents designers with several technical and operational challenges. A major issue is that the range of the signal is reduced due to propagation losses. This is one reason why deploying millimeter wave 5G will require more base stations than 4G. We need to have an optimal number of millimeter wave base stations to make 5G millimeter wave commercially viable, while also using beamforming of millimeter wave signals to ensure that mobile phones receive a strong enough signal. When designing massive multiple-input, multiple-output (MIMO
)
antennas, the higher frequencies mean that the size of the transmit/receive elements is much smaller than for 4G, resulting in a smaller physical size for the multiple millimeter wave antenna elements required for beamforming arrays. Beamforming (also known as beam steering), which uses a combination of analog phase shifters and digital control techniques to dynamically focus the output power into a single lobe, can optimize the signal-to-noise ratio and bit error rate for any signal path.
mmWave Interconnect Challenges
One issue facing mmWave RF development when designing infrastructure is that for frequencies of 30 GHz and above, the materials used for product PCB substrates can introduce signal losses and negative propagation effects. Ideally, a lower substrate dielectric constant (Dk
)
is desired
. As a result, the industry has begun to adopt thinner PCB dimensions and different substrate materials, such as polytetrafluoroethylene
(
PTFE) laminates. Solderless compression connectors have traditionally been used to make coaxial connections between stripline boards and antennas. However, as the frequency increases, the substrate becomes thinner and softer, and the substrate on the PCB is compressed, creating a capacitive effect that causes reflections, which in turn negatively affects the voltage standing wave ratio
(
VSWR), reducing link performance and transmitter efficiency.
Amphenol SV Solutions
Amphenol SV Microwave LiteTouch Series
Rather than using a solid mating connector interface, solderless PCB connectors use a ball-contact spring-loaded pin assembly to minimize the transfer of mating torque to the host assembly (
Figure 1
).
Figure 1: On the left is a traditional solderless compression connector showing deflection of the PCB substrate. On the right is the Amphenol SV Microwave LiteTouch solderless connector, which does not exert deflection or compression forces on the PCB assembly. (Source: Amphenol SV Microwave)
The screw-mount LiteTouch series is designed for use with 2.92mm, 2.4mm, and 1.85mm connectors. SMA versions are also available. The 2.92mm connector is designed for 50Ω impedance and is rated up to 40GHz, the 2.4mm connector is rated up to 50GHz, and the 1.85mm connector is rated up to 67GHz. The SMA connector is suitable for applications with frequencies up to 26.5GHz. In addition to the board-mounted version, a PCB edge-mount series is also available.
Figure 2
shows the effect on
VSWR
reflections
using standard compression connectors that can exceed 30 GHz
, as shown in the red curve. In contrast, the increase in reflections is minimal when using the Amphenol SV Microwave LiteTouch connector, as shown in the blue curve.
Figure 2: VSWR comparison of standard compression connectors and Amphenol SV Microwave LiteTouch connectors over the frequency range of 0 GHz to 40 GHz. (Source: Amphenol SV Microwave)
In addition to use in 5G infrastructure such as antennas, front-end modules and beamformers, designers can also use the Amphenol SV Microwave LiteTouch connector series in a variety of RF devices as well as high-speed digital test and measurement equipment, RF trays, and development and prototyping boards.
For more information on the LiteTouch connector series, please visit:
https://www.mouser.cn/new/sv-microwave/amphenol-sv-microwave-litetouch/
About the Author
Robert Huntley is an HND qualified engineer and technical writer. With a background in telecommunications, navigation systems, and embedded applications engineering, he writes a variety of technical and practical articles on behalf of Mouser Electronics.
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