The appearance in the near future of high performance consumer products, such as 3G mobile communications and high definition TV, are pushing the operating parameters of classic RF connectors such as BNC, SMA and N-Type.
The design and use of BNC connectors has had to adapt to keep up with the ever increasing demand for greater bandwidth. According to suppliers, the challenge seems to lie not only in the basic design of this connector range, which was designed for 50Ohm applications alone, but also on the way in which the connector is terminated.
This makes the PCB layout and the connector-to-board interface equally as important as the intrinsic properties of the connector.
With this in mind, when re-engineering its true 75Ohm BNC connector, Cambridge Connectors also incorporated a new style of PCB edge mounting. The attraction of this is it provides a straight signal path along the connector, through the point of interface and onto the PCB track with minimal loss of transmission characteristics.
The resultant VSWR of 1.09(max) over a frequency range of 0–1.5GHz and working voltage of 500Vrms puts the connector in line to meet HD Serial Digital Video requirements. An added benefit is that the card edge style has a lower profile.
Cambridge Connectors also offers True 75Ohm BNC patch leads in either standard length or built to customer specification. A 75Ohm optimised PCB layout guide is available on request.
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Huber+Suhner's connector-based switch can
replace RF relays
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Connector suppliers are looking for ways to apply their experience of RF signalling to applications such as 3G mobile comms. For example, a Huber+Suhner RF power switch is designed for channel switching in basestations, replacing electronically controlled RF relays.
According to the supplier, the use of a mechanical RF switch can lead to a more straightforward and cost-effective PCB design.
Available with a standard TNC interface, the RF power switch features a frequency range from DC up to 4GHz and can handle continuous power up to 80W.
Tyco Electronics offers a style of micro-miniature RF connector for direct board-to-board connections. These connections have typically been achieved by using either two cable connectors or perhaps two board connectors with a third, spacer or bullet, between. This can add cost and design complexity.
According to Tyco, a neater approach is the one connector assembly with spring-loaded contact, effectively replacing two or more connectors. One side of the Tyco compression connector is soldered on the base circuit board surface and the other side mates directly on the opposite target board using applied spring pressure. The design offers large radial and axial misalignment tolerance, which can reduce the risk of breaking soldered connections when mating or un-mating.
One multi-vendor, RF connector interoperability grouping worth noting is the Quick Lock Formula Alliance of suppliers of QMA and QN connectors, which are snap-on versions of established threaded SMA and Type N connectors. The alliance was initiated by Huber+Suhner, Radiall, Rosenberger and Amphenol RF to ensure ‘painless’ product intermateability.
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75Ohm optimised PCB layout
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With medical systems being another application for RF connectors, Radiall has recently introduced a range of SMA connectors which are non-magnetic.
In MRI scanning equipment the large magnet field (0.3-7Tesla) created by the equipment can cause interference issue with the system electronics. Any connector located in the magnetic field, should be transparent relative to the field, which means its relative permittivity should be equal to one.
With standard connectors, when an external magnetic field is applied, a magnetisation appears inside the connector. This magnetisation generates a disturbing field, thus the quality of the picture is poor and many corrections have to be made.
One approach is to use non magnetic materials such as brass, gold, silver or bronze and avoid the use of materials like stainless steel or nickel plating.
Radiall goes further and uses materials adapted to non magnetism with relative permittivity close to one. Each rod is selected based on a direct measurement with a vibrant magnetometer.
Centre contacts are gold plated over a copper underplate and bodies are plated with BBR, diamagnetic alloy of copper-stain-zinc or with GBR, diamagnetic alloy of copper-stain-zinc with a gold strike. The technology is available for SMB, MMCX and SMA series connectors.