Making the Most of PCB Materials for 5G Microwave and mmWave Amps


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Millions of cell phones trying to connect voices and download unimaginable numbers of files worldwide point to the inevitability of fifth generation (5G) wireless communications networks. 5G is coming, and it will require the right circuit materials for many different types of high-frequency circuits, including power amplifiers (PAs). 5G represents the latest and greatest in wireless technology, and it will be challenging to design and fabricate, starting with the circuit board materials, because it will operate across many different frequencies, such as 6 GHz and below, as well as at millimeter-wave frequencies (typically 30 GHz and above). It will also combine network access from terrestrial base stations and orbiting satellites. But by careful consideration of mechanical and electrical requirements, high-frequency circuit materials can be specified that enable the design and development of 5G PAs no matter the frequency.

Ideally, a single circuit material would be a suitable starting point for PAs at all frequencies. However, amplifiers at different frequencies have different design requirements and are best supported by circuit materials with different characteristics best suited to the different frequencies. For example, insertion loss or dissipation factor can be more or less depending on the type of circuit material. Every circuit material will suffer some amount of loss, which typically increases with increasing frequency. The loss performance of a given circuit material may be acceptable within the microwave frequencies to be used in 5G networks but not within the millimeter-wave frequency range, where signal power tends to be less with increasing frequencies. The circuit material that provides the low loss needed for high PA gain and output power at microwave frequencies may not be the best choice of material for a PA at millimeter-wave frequencies.

The design requirements for a key circuit material parameter, dielectric constant (Dk), are much different for microwave frequencies, such as the 6 GHz and below used with 5G systems, than for millimeter-wave frequencies, such as 30 GHz and above, as will be used for short-range backhaul links in 5G wireless networks. Selecting an optimum circuit material for each band of frequencies requires understanding which Dk value best supports each of the two different frequency ranges. Then it is a matter of finding circuit materials that possess those Dk values along with as many as possible of the other circuit material attributes that help make a good, high-performance, high-frequency PA.

To read this entire article, which appeared in the May 2018 issue of Design007 Magazine, click here.

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