High frequency connectors

If the connectors are to be used in high frequency applications, they must be made of plastics with low dielectric loss to avoid either damage to the part or signal loss in the circuit. 

Because ail the devices considered in this book operate at reiativeiy high frequency (>1 MHz), a singie connection aiways consists of two eiectricai contacts. In cases where the associated circuitry is remoteiy iocated from the device itself, these two contacts connect, via an appropriately designed RF-compatible connector, to the center conductor and the outer conductor (the shield — typically at ground potential) of a coaxial cable. 

Fluoropolymers are used to insulate wire for critical aerospace and industrial applications where chemical and thermal resistance is essential. They are also materials of construction for connectors for high-frequency cables and for thermocouple wiring that must resist high temperatures. 

Induction heating equipment, microwave comptinents, connectors, high-voltage electron tube bases, ncwi lamp holders and insulators, insulation plates, capacitor end plates, power station panel components, I eed-tbrough insulators, relay spacers, computer components, high frequency insulation components, arc barriers, microwave components, substrates, seals. 

Loss in connectors is negligible, except for small (SMA and BNC) connectors at frequencies of several gigahertz and higher. Small connectors used at high frequencies typically add 0.1 dB of loss per connector. 

In electronic connectors for use at high frequencies, PTFE is a standard material due to its low dielectric constant. This dielectric property help minimize the loss of strength of signals being transmitted through the connectors. In thermocouple connectors, ETFE provides resistance to elevated temperatures. 

Figure A-15 compares the soimd reduction indices of a typical, multilayered flexible connector tested alone, with plates and with bolster and plates. All of the test results showed a sharp increase in performance at 250 Hz due to the plates. No satisfactory explanation can be offered at this stage for this effect, which may be related to the small size of the samples. But in the middle and high frequencies the results were generally as expected with the plate giving an additional attenuation of about 5 dB compared to the compensator alone. The combination of the plate and bolster gave an additional attenuation of between 10 and 15 dB compared to the flexible connector alone.

Applications Eiectricai/eiectronic parts (High Frequency magnetic bobbins, micro-motor parts, connectors, antenna horn covers, packaging). Domestic appliances (microwave components steam iron parts). ... 

Electrical Properties. Polysulfones offer excellent electrical insulative capabiUties and other electrical properties as can be seen from the data in Table 7. The resins exhibit low dielectric constants and dissipation factors even in the GH2 (microwave) frequency range. This performance is retained over a wide temperature range and has permitted appHcations such as printed wiring board substrates, electronic connectors, lighting sockets, business machine components, and automotive fuse housings, to name a few. The desirable electrical properties along with the inherent flame retardancy of polysulfones make these polymers prime candidates in many high temperature electrical and electronic appHcations. 

The high-power levels and frequencies at which vacuum tubes operate place stringent demands on the connectors used to tie the outside world to the inside elements. Figure 5.36 shows a cutaway view of the base of a tetrode. Tubes are designed to be mounted vertically on their electrical connectors. The connectors provide a broad contact surface and mechanical support for the device. 

When the PCB is thermally saturated and the component temperatures are still too high to be tolerated at the maximum obtainable system air velocity, other means of conducting heat from the PCB to even larger area system structures are required. The chassis of the system is often the largest surface area structure in the system, is exposed to the ambient air, and often makes a good sink for heat that cannot be dissipated by the PCB alone. Mechanisms to conduct heat into the chassis include chassis screws, gap fillers, connectors, and side rails. Sometimes, radio frequency (RF) shields that are appropriately connected to components can provide additional heat sinking. 

These plastics exhibit low dielectric losses and stable dielectric constants over a broad range of temperatures and frequencies. The chemical resistance of the materials is their weakest point. Although resistant to most common solvents, acids and alkalis, they exhibit stress cracking in the presence of organic ketones, esters and chlorinated hydrocarbons. Polysulphones are used in the electronics field for connectors, chip carriers and capacitor dielectrics, and they are the first of the high temperature thermoplastics to be used for printed wiring board fabrication. 

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