In terms of structural principle, the connector has three main parts: contact, insulator and shell.

 

1. Contact of connector. According to the structural form, it is divided into pinhole type, tuning fork type and curved reed type. Most of them include guide part, contact part, installation part and termination part.

2. The main function of the insulator of the connector is to support and fix the contact pairs and insulate them from each other; Install the attachment for the connector.

3. Connector housing. Its main function is the protection and shielding of machinery and environment; Support the installation of insulators;

 

SMA RF connector is often regarded as an element installed on cable or instrument, which is used as an electrical connection or separation element of transmission line. It belongs to mechatronics products. In short, it mainly acts as a bridge.

 

SMA RF connectors have many varieties and specifications, including more than 20 international general series, with more varieties and specifications. They rely on mechanical structure to ensure electrical characteristics. They are mechatronics products, which are essentially different from other low-frequency connectors. RF coaxial connector parts are mainly processed by turning machine. There are many manual assembly operations, so it is difficult to carry out automatic assembly, and the product renewal is slow.

 

SMA RF connector is an important part of the device, which is a labor-intensive product with a certain technical content. Reliability, failure mode and failure mechanism are complex.

 

Generally, the contact between the connector pin and SMA is the contact hole. We know that the pins or terminals of components generally have a layer of coating, such as lead tin alloy plating, pure tin plating, nickel plating, silver plating, silver palladium alloy plating, gold plating, etc. Therefore, the contact between components is actually the contact between these coated metals. Of course, the conductivity of different coated metals is different, and the corresponding contact resistance is also different. Generally, the conductivity of gold is better, followed by silver. In the welding process, because welding is actually the process of forming alloy, and the alloy itself is a good conductor, the reliability of welding itself is relatively high, unless it is poor welding. However, the connection between connectors depends on the contact between surfaces, so it is easy to cause poor contact

 

 1、Introduction of SMA connector


SMA is usually used to provide RF connection between circuit boards. Many microwave components include filters, attenuators, mixers and oscillators. The connector has a threaded external connection interface, which has a hexagonal shape and is allowed to be tightened with a wrench. Special torque wrenches can be used to tighten them to the correct tightness, so that a good connection can be achieved without over tightening.

 

The first SMA connector is designed for 141 semi-rigid coaxial cables. The original SMA connector can be called the smallest connector because the center of the coaxial cable forms the connected center pin, and there is no need to make a transition between the coaxial center conductor and the center pin of the special connector.

 

Its advantage is that the cable dielectric is directly connected to the interface without air gap, while its disadvantage is that only a limited number of connection / disconnection cycles can be carried out. However, for applications using semi-rigid coaxial cables, this is unlikely to be a problem because the installation is usually fixed after initial assembly.

 

2、Performance of SMA connector

 

The SMA connector is designed to have a constant impedance of 50 ohms on the connector. SMA connectors were originally designed and designated for operation up to 18 GHz, although some versions have a top-level frequency of 12.4 GHz and some versions are designated as 24 or 26.5 GHz. A higher upper frequency limit may require operation at a higher return loss.

 

In general, SMA connectors have a higher reflection coefficient than other connectors up to 24 GHz. This is due to the difficulty of accurately fixing the dielectric support, but despite this difficulty, some manufacturers have managed to appropriately overcome this problem and can specify their connectors for 26.5ghz operation.

 

For flexible cables, the frequency limit is usually determined by the cable rather than the connector. This is because the cables accepted by SMA connectors are very small, and their loss is naturally much greater than that of connectors, especially at the frequency they may be used.

 

3、 Termination mode of SMA RF connector

 

1. Wiring type

 

Wiring is divided into welding wire type and crimping connector. Welding wire type is to weld the central conductor and cable shielding layer. Crimping type is to crimp the central conductor and cable shielding layer. The crimping type has high efficiency and good performance. Welding wire type is stable and reliable. Generally, flexible cables are mostly crimped, and semi flexible cables and semi steel cables are mostly welded.

 

2. Connected to PCB (printed circuit board)

 

When the connector is to be connected with PCB, it is mostly through hole or SMT. In order to be easy to tin, the metal connected with PCB is mostly gold-plated or tin plated.

 

SMA:

 

1. Male and female: if the thread is outside and the central needle is the hole, it is the female head, and if the thread is inside, the central needle is the needle, it is the male head

 

2. Reverse pole: the female head has a needle, that is, the thread is outside, and the central needle is a needle, which is the reverse pole female head; The male head is equipped with a needle, that is, the thread is inside, and the central needle is a hole, which is a reverse pole smooth head

 

3. Butt joint mode: thread butt joint

 

4. Impedance：50 ohm

 

5. Tooth gauge: 1 / 4-36uns-2b, 1 / 4-36uns-2a

 

6. Frequency: 0-6GHz, some customization can reach 12GHz and 18GHz