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34 DESIGN007 MAGAZINE I FEBRUARY 2019 The frequency spectrum is being consumed quickly for many wireless applications from popular cellular communications systems to more esoteric safety and medical systems. For the available spectrum, circuit designers are reaching beyond traditional microwave frequencies and into the millimeter-wave (mmWave) frequency ranges from 30–300 GHz. Those designers often look to a relatively mature technology, flexible circuit technology as the PCB materials for those high-frequency circuits. Although such materials may not typi- cally be a first substrate choice for high-speed, high-frequency circuits, the thinner, flexible circuit materials are well suited for the shorter wavelengths at mmWave frequencies. Such high-frequency signals are being planned for global communications in fifth- generation (5G) wireless systems, automotive driver assistance system (ADAS), and self-driv- ing autonomous vehicle systems, among other applications. Thinner substrate materials have several advantages for high-frequency circuits. For example, thinner dielectric materials be- tween copper circuit planes can help minimize internal resonances in the circuits. Thicker cir- cuit materials can suffer higher electromagnet- ic (EM) radiation losses to neighboring circuits and can lose energy as EM interference (EMI) at higher frequencies where signal wavelengths are smaller and signal power can be harder to come by. Circuits designed for mmWave fre- quencies usually start with thinner circuit ma- terials for optimum performance. The smaller wavelengths of mmWave fre- quencies tend to highlight circuit material anomalies at those higher frequencies—anom- alies that can also influence the radio frequen- cy (RF) performance of the circuit. Such mate- rial anomalies include variations in dielectric thickness, dielectric constant (Dk), copper conductor width and spacing, and copper con- Higher Frequencies Pave Way for Flexible Circuit Materials Lightning Speed Laminates Feature Column by John Coonrod, ROGERS CORPORATION

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