Issue link: https://resources.mouser.com/i/1541351
31 | or PCB traces using fine wires. Wire bonding is mostly used to connect chips with packaging or bare die to an RF circuit board. This interconnect technology requires specialized wire bonding machines to properly and reliably connect wire bonds, which is why wire bonding in large volumes is typically done using automation. Probes allow temporary or repeated connections in RF circuits and are commonly used in automated testing, diagnostics, and high- frequency measurement setups. A wide variety of probe technologies exists, including spring probes, spring pins, and transmission line arrangements that use multiple probes in a probe head. Contactless probe designs also use near-field antennas, open-ended coaxial lines, and even waveguides. Coaxial Coaxial transmission lines are one of the most common types of RF interconnects used beyond the chip and circuit board level. These transmission lines are used for board-to-board connections, within modules, between modules, and between systems. A benefit of coaxial transmission lines is that the outer conductor also acts as a shield that prevents internal signal leakage and external signal ingress into the transmission line environment. These properties and the relatively efficient transmission of signal energy along a coaxial line have led to the widespread use of coax in RF, high-speed digital signaling, precision measurement, and many other applications. The main physical components of a coaxial transmission line are a coaxial cable and connectors. However, there are some applications where the coaxial cable is directly attached to other transmission lines, or a coaxial connector may be the interface to another transmission line, such as with end-launch coaxial connectors (Figure 4). Coaxial transmission lines are characterized by cylindrical, coaxial inner and outer conductors that are separated by a dielectric barrier (Figure 5). Within a coaxial transmission line, the magnetic field lines follow a circular path around the inner conductor and between the inner and outer conductors. The electric field lines Figure 4: A coaxial cable with center conductor and shielding exposed and an end launch coaxial connector. (Source: Mouser Electronics) are perpendicular to the magnetic field lines and radiate from the inner conductor to the outer conductor. This transverse electromagnetic (TEM) mode of operation leads the Poynting vector to point along the length of the coaxial transmission line. This behavior results in relatively simple derivations of the ideal characteristic impedance, inductance per unit length, capacitance per unit length, voltage, current, and other transmission line behavior. In the following equation, Z is the characteristic impedance, η is the wave impedance, μ is the magnetic permeability, ε is the relative permittivity of Figure 5: A diagram of a coaxial transmission line with conventions for inner diameter (a), outer diameter (b), and the direction of the E-field and H-field. (Source: Orfanidis, Electromagnetic, 546, 11.4.1) 4