Finding The Right Circuit Materials For Communications Antennas
Everyone has seen those tall antenna towers that make our modern communications possible. They often hold multiple antennas, facing in different directions, to enable cellular phone calls and transfers of data and video files. And those antennas work, rain or shine, in summer and winter, with reliability that most people take for granted. But what they may not realize is that many of those antennas depend on the durability and repeatability of the printed-circuit-board (PCB) materials on which they are formed. And the right circuit materials can make a big difference on how well those tower-mounted antennas perform!
Rogers invested a great deal of time and research into finding the right circuit materials for printed-circuit antennas for communications and other high-frequency applications. The type of material has a strong impact on the size and performance possible from an antenna. A printed-circuit antenna is typically fabricated on a PCB material composed of a dielectric layer with copper on one or both sides. For reliable electrical performance, that combination of copper and dielectric must be consistent, over time and over temperature. Understanding some of the key PCB material parameters and how they relate to antenna performance can pay large dividends for those working with PCB-based antennas.
One of those key PCB material parameters for antennas is dielectric constant, also known as relative permittivity. Circuit materials for antennas usually have dielectric constants in the range of about 2.5 to 10.3, as measured in the z-axis or thickness of the material. In terms of PCB antennas, materials with higher values of dielectric constant support smaller antennas for a given frequency, but with somewhat less gain than the larger antennas fabricated on dielectric constants with lower values.
Weight is another important parameter for any tower-mounted antenna, especially when it must handle high wind loads. For that reason, Rogers developed specialty materials such as its RO4730™ LoPro™ antenna-grade circuit materials that are a fraction of the weight of other high-frequency circuit materials with comparable performance. Rather than use a solid dielectric layer, the RO4730 LoPro circuit materials use hollow glass microspheres as a filler material to cut weight, but not performance. The RO4730 LoPro circuit material has a low dielectric constant of 3.0 in the z-axis and features low-profile copper to minimize signal loss and distortion. It is also compatible with low-cost FR-4 circuit materials and circuit processing methods.
Another Rogers circuit material ideal for high-performance antennas is ceramic-filled RO4500™ laminate, available in several values of dielectric constant from 3.3 to 3.5. Especially for antennas that must handle higher power levels, such as in radio transmitters, Rogers RO4500 circuit materials excel in several important parameters related to power-handling capability. They feature high thermal conductivity for good heat flow, and they are mechanically stable across a wide temperature range, formed of a dielectric material with coefficient of thermal expansion (CTE) in the x and y directions closely matched to that of copper and overall low z-axis expansion.
These are just two examples of Rogers’ circuit materials well suited for communications antennas. Every antenna is different in terms of size, shape, and performance and Rogers’ engineers can help you find that perfect circuit material for the antenna you have in mind.