This blog will attempt to “see through” the effects of glass on high frequency circuit boards, especially on the millimeter-wave circuits that are becoming so important in emerging automotive radar systems (at 77 GHz) and Fifth Generation (5G) cellular wireless communications systems.

The characteristics of circuit materials have a great deal to do with how well a printed circuit board (PCB) performs, especially at RF/microwave frequencies. Circuit material parameters such as dielectric constant (Dk), dissipation factor (Df), even material thickness can affect the way that different transmission lines, such as microstrip, stripline, and coplanar waveguide, perform in high-frequency circuits. Fortunately, there is a simple and pain-free way to predict how different high-frequency transmission lines will behave when fabricated on different circuit materials: the Microwave Impedance (MWI) Calculator software.

Skin depth is often used to describe the behavior of current flow through circuit conductors, i.e., the copper on a PCB, especially at RF/microwave frequencies. Direct current (DC) may exhibit evenly distributed flow through a conductor such as copper, but high-frequency, sinusoidal current experiences changing energy density as it flows through a PCB’s conductors, with areas of lower and higher current density relative to the surface of the conductor.

As explained in the previous ROG Blog, vehicular radars are already being designed and fabricated at millimeter-wave frequency bands such as 77 GHz. Specifiers of circuit materials for millimeter-wave frequencies (30 to 300 GHz) are faced with special requirements that are often different than those for circuits at microwave frequencies of 30 GHz and below. However, practice and experience of circuit designers working at millimeter-wave frequencies has shown that some circuit material parameters can be tightly linked to achieving high performance in millimeter-wave circuits, and that some circuit materials embody the material parameters as needed for excellent performance at 77 GHz and beyond.

This ROG BLOG is Part One of a two part series introducing the key criteria to consider when selecting a PCB substrate which will minimize circuit losses for 77 GHZ radar PCB antenna applications.  First we will discuss components of PCB circuit loss, and then introduce six key material properties critical to developing low loss millimeter wave circuits at 77 GHz.

Unwanted levels of PIM can result from several different factors, including the amplitudes and frequencies of the multiple transmitted tones, the configuration of a circuit’s transmission lines, and the current density and power level of the application. Multiple signal tones are usually denoted by their fundamental frequencies, such as f1 and f2, with the frequencies of their PIM spurious signals resulting from the differences between different harmonics of the fundamental tones. Learn about how PCB designs can reduce PIM.

Advanced automotive electronics systems have relied on the reflections from on-board vehicular radar systems for some time. The vehicular radars are often fabricated on what are known as hybrid multilayer PCBs. These are PCBs formed of different kinds of circuit-board materials, matching the characteristics of the different materials to the needs of the different circuit functions, from DC through 77 GHz. Learn about designing with these new layers to realize better performing circuits at a lower cost.