Impact of mmWave Signals on PCB Traces,RF Test Cables, and Connectors

The use of mmWave technology is growing in a variety of applications, from 5G phones to automotive systems and drones. At mmWave frequencies, signal integrity (SI) is a major concern. SI measures the ability of a signal to propagate without distortion or undue loss. It measures the quality or distortion of signals passing through printed circuit board (PCB) traces, rf test cables, and connectors in a system. Signal distortion can disrupt reliable system operation and occurs due to impedance mismatches, reflections, ringing, crosstalk, jitter, ground bounce, and more.

Depending on the signal modulation scheme used and other factors, SI optimization takes different forms. For example, the need to control ringing is critical for signals using ASK, PSK, QAM, QPSK, or any other signal modulation scheme that uses sudden changes in phase or amplitude to encode digital information. For sufficiently smooth FM schemes such as FSK, the effect of ringing is less.【rf test cables】 Ringing is just one aspect of SI. Additional SI and PCB layout considerations include:

Controlling impedance ensures that the signal rf test cables  has matching source and receiver impedances that are the same as the impedance of the signal line itself.Impedance discontinuities need to be managed and minimized and can occur at vias in the signal path, branches in the signal path, wire ends, when the signal wire mates with the connector pins, and when the signal rf test cables starts at the source and/or at the signal wire Receiver at the end.
Propagation delay can be minimized by matching trace lengths.

Crosstalk noise can be controlled by increasing the spacing between adjacent signal traces, using lower dielectric constant substrate materials, using differential signals with tightly coupled differential pairs, and ensuring that the signal rf test cables path is as wide and uniform as possible.
Power and ground distribution issues, including ground bounce, can be addressed using a variety of design techniques, including placing decoupling capacitors as close as possible to the power and ground pins of the device, and placing power and ground planes close to and close to the PCB surface to Reduce via inductance.【rf test cables 】Controlling impedance is the most important factor in preventing SI issues in mmWave PCBs. Interconnect geometry is important for determining and controlling impedance. Trace shape is a complicating factor, including losses due to dielectric absorption, skin effect, roughness losses, and scattering, in addition to adequate isolation.

High frequency rf test cables  often rely on microstrip or stripline transmission line geometries and protective vias to isolate different circuit blocks and reduce radiated emissions. Another method is to use grounded coplanar waveguide (GCPW) routing, which provides lower losses and stronger isolation, especially on the surface layer, than the other two routing methods.