Coaxial Electromechanical Switches

Applikationsberichte

Introduction 

Keysight Technologies, Inc. is the global leading designer and manufacturer of coaxial electromechanical (EM) switches, with a long history and proven track record for high performance, quality, and reliability. Coaxial EM switches provide the reliability and performance required by automated test systems used in the aerospace and defense and wireless communication industries for signal monitoring and routing purposes. One of the most common applications of coaxial EM switches is mobile handset testing in the wireless communication industry. 

According to a research study1 , global mobile handset shipment is on track to reach one billion units shipped in 2006, representing a 22.5% growth over 2005. This impressive growth rate places high emphasis on the reliability and performance of automated test systems (ATS) used for mobile phone testing, of which the EM switch is a major component. Two of the most important considerations when selecting an EM Switch are operating life and repeatability. 

This application note describes: 

  • The operating life of EM switches, the jumper contact mechanism of conventional EM switches, and the Keysight contact mechanism with its wiping-action technology. 
  • Finally, the effect of repeatability on measurement uncertainty is discussed.

Operating Life of an EM Switch

The operating life of an EM switch can be defined as the number of cycles the switch will complete while meeting all RF and repeatability specifications. The operating life refers to the electrical life of the switch, and not the mechanical life (which is much longer than the electrical life). One life cycle is defined as one closing and opening of the jumper contact (sometimes referred to as switchblade) or one on/off triggering of the electromagnetic coils in the switch. The operating life is very dependent on the jumper contact mechanism, contact resistance, and the material and plating used in all the key RF components of a switch. Keysight coaxial EM switches are produced with meticulous manufacturing processes and stringent quality assurance systems. 

Conventional EM Switch Contact Mechanism 

Conventional switches function by moving a thick rectangular contact known as a jumper contact (or switchblade) inside the RF housing. The jumper contact is joined by a push rod, generally made of a dielectric material such as Polystyrene (PS) that moves inside an access hole in the RF housing. The tip of the jumper contact is directly pressed onto the flat surface on the tip of the center conductors of the connectors by a mechanical spring force from the actuator.

The jumper contact is usually thick and inflexible, as can be seen in Figure 3. The vertical motion of the jumper contact and push rod during opening and closing results in what is sometimes referred to as “frictionless switching”, since there is no friction produced between the jumper contact and center conductor.

This configuration produces switches that can mechanically actuate for tens of millions of cycles. However, there are some drawbacks. 

The continuous impact between the jumper contact and center conductor will gradually result in increased wear and tear, producing some debris. The debris, along with dirt and contamination accumulated over time remains on the tip. As a result, contact resistance increases over time leading to increased insertion loss. This may or may not result in the switch failing its RF specifications, but will have a significant effect on the insertion loss repeatability of the switch. The random nature of this particle buildup also means that such failure can be intermittent, and may not be detectable. This buildup is the result of an inflexible jumper contact. The particles remain trapped on the surface of the center conductor throughout the life of the switch. Switches with designs of this nature usually have loose repeatability specifications or none at all, with possible failures occurring intermittently throughout the lifetime of the switch.

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