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New for February 2025. You are integrating an expensive module that includes a switch function. There are lots of challenges, meeting requirements but your solution is a winner. Then you assemble a pile of modules and find that a good percentage of them have a suck-out in the band. What could cause that? A bad connector! In his case, the design required a female TK connector, practically a unicorn, left over from the 1970s. But bad connectors exist in all species.
Here is the performance of the switch in its low-loss state, for a good unit.
Here is a unit that has a suck-out at 15.6 GHz. We saw many other units with similar suck-outs between 15 and 16 GHz.
What's going on?
Let's look inside the RF connectors. Here is a good one. Note that the four spring fingers are touching, or nearly touching each other. They are made of beryllium-copper, an alloy that is known for maintaining spring force. However, they have to be formed properly in order for them to work.
Here is a mis-formed connector. See the gaps between the spring fingers? That is not a good sign. This one has OK performance, but it is borderline bad and should replaced before you put your name on the product and ship it.
Here is a confirmed bad connector. It caused the suck-out shown in the S-parameter plot shown above.
Can you simply bend the spring fingers back? No, that would be like trying to bend the springs on your car to make it sit higher. Not going to happen. And you will damage the PTFE dielectric.
Why does a bent spring finger cause a suck-out? Think of it as a low-Q open-circuit stub. The length of the spring finger is a quarterwave at the suck-out frequency.
Supposer you bought connectors from a reputable US manufacturer, but it turns out that up to 50% of them show this undesirable characteristic to some extent. The next step is to get the connector supplier to admit they goofed, and to ship you some good product. One complicaion is that TK connectors ar not a calalog item and might take 12-18 weeks to fabricate more. You will soon b remind of the conversation you had with an insurance agent when some texting teenage tool plowed into your car when you were sitting at a stoplight, causing you to hit the car in front of you. Are you sure you had your foot on the brake? Give me a break. Are you sure you didn't damage these female connectors by mating them to a bad male connector? Well, that's a good question, especially since you supplied the male connectors... This talk is very annoying, especially if you saw this problem on connectors right out of the bag, unused.
If anyone wants to know what connector company provided these problematic connectors, just ask. There are very few suppliers for TK connectors, by our count there are only three, and all of them in the United States. Made in USA does not carry the weight it once did.