This spring-lock design can be applied to all threaded-interface connectors, and is built to maintain electronic and mechanical performance.
Within the RF industry, replacing connectors that have a threaded interface with those that have a quick-lock coupling mechanism is a growing trend. The clearest evidence lies in the increasing number of competing quick-lock SMA (QMA) and Type N (QN) connector designs that have appeared on the market in the last five to six years. Nearly every leading RF connector manufacturer now includes one or both in their product lines.
The reason these connectors were designed in the first place can mainly be attributed to OEMs like Ericsson, Motorola and Nokia, who wanted to increase the speed of installation as well as to package connectors more closely together in their wireless base stations.
Yet given the wide range of sources and the obvious advantages of a snap-on coupling mechanism over a threaded interface, it is surprising that the sphere of applications for quick-lock connectors has not spread much beyond base station applications. The reason is that current quick-lock connectors must improve considerably in terms of electronic performance, reliability, and the amount/cost of raw materials needed for manufacture before they are considered viable alternatives to the SMA and Type N.
In short, quick-lock connectors must begin to match the performance of the threaded connectors they were designed to replace.
An across-the-board solution
This was the goal for the research and development team at Anoison Electronics (www.anoison-electronics.com), but to achieve it, designers took an unusual tack. Rather than design a quick-locking mechanism around a specific connector, like the SMA or type N, they sought to create a locking mechanism that could be applied across the board—to all connectors having a threaded interface.
These efforts produced four basic design principles for a new spring lock coupling mechanism:
It has to work; that is, the connector can be repeatedly snapped easily into place and still provide a strong holding force;
Internal structural parameters of the original threaded connectors must be altered as little as possible;
It must be simple, requiring very few raw materials;
It must be able to provide the new quick-lock connector with electronic and mechanical performance equivalent to the threaded connector it is meant to replace.
The key to a successful new quick-lock design lay in its ability to satisfy these fundamental requirements. So, Anoison engineers researched, analyzed, and tested representative quick-lock connectors on the market, primarily:
QMA (U.S. patent #6,692,286);
QN (U.S. patent # 6,709,289);
1.0/2.3 Series.
The SnapN from Rosenberger (www.rosenberger.de) and the QLS (a quick-lock SMA connector) from Telegartner (www.telegartner.com) and IMS (www.imscs.com) were also examined closely in an effort to discover the best quick-lock mechanism and to come up with new design ideas.
Early on, designers found that creating a working locking mechanism for a specific connector was relatively easy, or at least common, since all the connectors tested satisfied the “it has to work” requirement. The difficulty arose when trying to find a locking mechanism that could be applied to a range of RF connectors because of the variation in the power-handling capability among different connector types. 
FIGURE 1 & 2. Despite operating in different power ranges, both CQMA (top) and CQN (bottom) connectors feature the same basic spring-lock mechanism and, according to designer Anoison Electronics, are able to offer performance equivalent to the connectors they were designed to replace.
When looking at connectors used for low-, medium- and high-power transmissions—in this case, the SMA, Type N and 7⁄16 respectively—designers immediately discovered that there was no spring lock available that could be applied to all three connectors—the QMA or QLS locking mechanism would not work in the Type N, the QN or SnapN locking mechanism likewise would not work in the SMA, and none of the quick-lock mechanisms could be used to create a snap-on 7⁄16 connector. The reason is that these locking mechanisms can significantly alter the internal construction of the original connector, which in turn directly affects the power range in which it is suited to operate.
Anoison researchers also found few locking mechanisms that were simple and economical, with the majority being at once cleverly designed and yet complicated. Plus, the materials needed to manufacture them are expensive (often requiring berrylium copper), they require a high degree of processing accuracy, and a large amount of material is wasted. It all added up to very high production costs.
Upon comparison, Anoison designers determined that the most efficient locking mechanism belonged to the 1.0/2.3 connector, which has a stamped stainless steel spring lock. Adopting this design requires a large initial cost to create the mould for stamping. But the subsequent manufacturing cost is very low, and the processing requirements are simple so that the original investment can be quickly recovered. Even so, designers believed that even if this type of spring lock were applied to the SMA or Type N, it would still require modification so it could operate in higher frequencies.
Modified stainless steel design
In fact, the primary concern with each quick-lock connector Anoison engineers examined was the inability to meet the electronic and mechanical performance parameters of the SMA and Type N. This is not surprising since the SMA and N have been optimized for performance over the years, and is another reason why when replacing the coupling mechanism it is essential to change the rest of the connector’s inner construction as little as possible.
When compared to the SMA and Type N in terms of continuous impedance, contact reliability, IP grade seal and the degree of contact force between the outer conductors (this determines passive inter-modulation performance—or, PIM), in one way or another, the QMA, QLS, QN, SnapN and 1.0/2.3 all failed to meet the high standards set by the originals. In the case of the 1.0/2.3, the main problem was that the spring lock allowed clearance between the outer conductors at the contact interface. The SMA and Type N achieve high frequency bandwidths and continuous impedance with almost no reflection because of the rigid contact and zero clearance between their conductors. By allowing a gap, the 1.0/2.3 is only really suited to work in lower frequencies.
FIGURE 3. A modification of the 1.2/2.3 stamped spring-lock connector involved designing teeth of varying lengths that snap into place upon mating, forcing the ends of the outer conductors into close contact and maintaining a strong axial force.
Since it had already been determined that the 1.0/2.3 stamped spring lock had considerable economic advantages, engineers decided to modify the stainless steel design to solve the clearance problem. They took advantage of an upslope, or bulge, on the outer conductor of the QMA female (see Figure 3) and applied the principles of leverage mechanics.
By designing a spring with teeth of slightly variant lengths that project out at a certain angle, and then positioning this spring properly inside the plug, the teeth of the spring snap into place behind the bulge on the outer conductor of the jack after mating the connector, forcing the ends of the outer conductors into close contact and maintaining a strong axial force.
Additionally, this spring lock design has the benefit of being very unobtrusive so as to also allow room within the plug to accommodate an O-ring.
After two years of research and testing, the new spring lock was patented this year, and two new Quick-lock SMA and Type N connector designs were released by Anoison Electronics—the CQMA and CQN (see Figure 1 and 2, page 15).
Despite operating in different power ranges, both CQMA and CQN feature the same basic spring-lock mechanism and both are able to offer performance equivalent to the connectors they were designed to replace.
Having established the versatility of this spring-lock design, Anoison designers are now working on modifications that will let it fit into the 7⁄16 DIN connector, and hope to have a quick-lock solution by next year.
ZHOU WEIQUAN is an engineer with RF solutions provider Anoison Electronics (www.anoison.com). Translation assistance for this article was provided by James Dolan, marketing and sales manager.(end)
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