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I have an independent PCB design for a standard SMT-placed antenna. There are large ground planes on both side.

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I can understand that the thickness is going to change the values of the matching network but I'm wondering if the thickness impacts the best optimization possible. In other words, is there an optimal PCB thickness for such kind of design? Or can I do as thick as I want? Is thinner or thicker better?

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Here are two aspects in printed antenna design;

  1. Thickness of PCB substrate: Substrates with higher thickness and a high dielectric constant result in smaller bandwidths and lower efficiencies due to the possibility of surface wave excitation. The substrate thickness should be made as thin as possible to eliminate multiple surface waves. A height of 0.01λ0 to 0.05λ0 is considered ideal in this regard.
  2. Thickness of conducting metal in PCB: The thickness t of a metallic layer must be a substantially smaller than the wavelength of the free space (t << λ0) for a given frequency. Select materials and thickness of conductor required for mechanical integrity. Because of the skin effect there is no point in using thick conductors unless it is cost-effective or sturdier. Due to skin effect, RF current flows only on the surface of the conductor and there is no need to use very thick metallization. Calculate the skin depth for your frequency of interest. For example: Copper at 2.4 GHz results in a skin depth of 1.33µm. This means that a "standard" copper thickness in PCB (e.g. 17µm) is perfectly fine. Using thicker copper will not reduce losses.
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If the antenna is SMD, you will have to solder it on top of your PCB and only the nearby ground planes will affect the performance of such antenna. The thickness of the substrate will be important whenever you are designing a printed antenna.

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