Electrical connector, adapter and test device with smooth impedance transition

An adapter, configured to electrically connect a first electrical element with a second electrical element, comprising an electrical connector, the electrical connector comprising:

• an outer shell defining a mounting hole, at least part of the outer shell being a metal shell;
• an insulating element installed in the mounting hole, the insulating element defining a through hole extending in an axial direction;
• and
• a central conductive terminal inserted into and at least partially extending through the through hole, the central conductive terminal comprising a first fitting portion, a second fitting portion, and an intermediate portion located between the first fitting portion and the second fitting portion;
• the central conductive terminal being configured to transmit a signal;
• when the signal is transmitted in the first fitting portion, it encounters an impedance having a first impedance value;
• when the signal is transmitted in the second fitting portion, it encounters an impedance having a second impedance value;
• the intermediate portion comprises an impedance transition area, and when the signal is transmitted in the impedance transition area, it encounters an impedance having a gradually changing third impedance value;
• wherein the first impedance value is different from the second impedance value;
• the first impedance value, the third impedance value and the second impedance value generally have a smooth transition;
• wherein one end of the electrical connector is electrically connected to the first electrical element, and another end of the electrical connector is electrically connected to the second electrical element.