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How to solve the millimeter wave reflection problem in the connector?

Author: Date:10/29/2019 6:36:14 PM
 5G opens a new situation

    With the growing momentum of the new generation of cellular communications 5G, the competition to deploy 5G communication infrastructure is also in full swing. Mobile operators are busy deploying infrastructure and launching marketing plans to attract everyone to upgrade their smartphone service contracts and handset configurations to take advantage of the significantly higher data rates of 5G. Unlike the previous generation of 3G to 4G, the 5G communication architecture is not an iterative upgrade. The 5G first used the frequency in the 24 to 40 GHz millimeter wave (mmWave) spectrum and coexisted with the multi-radio communication network in the licensed and unlicensed sub-6 GHz bands.


Use millimeter wave for 5G

    To achieve a significant increase in 5G data transfer speed (expected at least 4 times faster than 4G), a high bandwidth millimeter wave spectrum is required. But using such a high frequency presents designers with some technical and operational challenges. A major problem is that the range of signal coverage is reduced by propagation losses. This is one of the reasons why more base stations are needed to deploy millimeter-wave 5G than 4G. We want to make the 5G millimeter wave commercially viable with the best number of millimeter wave base stations, and also use the beamforming of the millimeter wave signal to ensure that the mobile phone receives a strong enough signal. In designing large-scale multiple-input multiple-output (MIMO) antennas, higher frequencies mean that the size of the transmit/receive elements is much smaller than 4G, making the physical dimensions of the plurality of millimeter-wave antenna elements required for the beamforming array smaller. Beamforming (also known as beam steering), which combines analog phase shifters with digital control techniques, dynamically concentrates output power into a single lobe that optimizes the signal-to-noise ratio and bit error rate for any signal path.


Millimeter wave interconnection challenge

    One of the problems with millimeter-wave RF development when designing infrastructure is that for products at 30 GHz and above, the material used for the product's PCB substrate can cause signal loss and negative propagation effects. Ideally, a lower substrate dielectric constant (Dk) is required. As a result, the industry has begun to use thinner PCB sizes and different substrate materials, such as polytetrafluoroethylene (PTFE) laminates. Establishing a coaxial connection between the stripline and the antenna has traditionally used a solderless compression connector. However, as the frequency increases, the substrate becomes thinner and softer, and the substrate on the PCB is compressed, causing a capacitive effect, causing reflections, which in turn negatively affect the voltage standing wave ratio (VSWR). Impact, resulting in reduced link performance and transmitter efficiency.


Amphenol SV Solution

    Instead of using a solid mating connector interface, the Amphenol SV Microwave LiteTouch Series solderless PCB connector uses a ball contact spring thimble assembly to minimize conduction of mating torque to the main assembly (Figure 1).



Figure 1: The left side is a conventional solderless compression connector that shows the deflection of the PCB substrate. On the right is the Amphenol SV Microwave LiteTouch solderless connector, which does not create deflection or compression forces on the PCB assembly. (Source: Amphenol SV Microwave)


    The screw-mounted LiteTouch series is designed for use with, and connectors. An SMA version is also available. The connectors are designed for 50Ω impedance, rated at up to 40GHz, with connectors rated up to 50GHz and connectors up to 67GHz. SMA connectors are suitable for applications with high frequencies. In addition to the on-board version, a PCB edge mounting series is also available.


Figure 2 shows the effect of a standard compression connector with a frequency of more than 30 GHz on standing wave ratio (VSWR) reflection, see red curve. In contrast, it can be seen from the blue curve that the increase in reflection is minimal when using the Amphenol SV Microwave LiteTouch connector.


Figure 2: Comparison of the VSWR of a standard compression connector to the Amphenol SV Microwave LiteTouch connector over the 0GHz to 40GHz frequency range. (Source: Amphenol SV Microwave)


    In addition to 5G infrastructure for antennas, front-end modules and beamformers, designers can also use the Amphenol SV Microwave LiteTouch connector family for a wide range of RF equipment as well as high-speed digital test and measurement equipment, RF trays, and development boards and prototyping board.