large variety of PCB-based antenna structures are used at microwave
frequencies, and some are used at higher frequencies. A common PCB antenna structure
is a microstrip patch antenna. A microstrip structure is a two-layer copper circuit
with a signal plane and a ground plane, but it is more common for this type of circuit
to be the outer layers of a multilayer circuit.
size of the copper feature or patch, for a microstrip patch antenna, has to do
with a fraction of a wavelength, usually ½ wavelength. The patch will transmit
or will be very sensitive to receive energy at a specific frequency, which is
related to the ½ wavelength circuit feature size. Wavelength is associated with
frequency as well as the dielectric constant (Dk) of the circuit material. Just
for reference, a higher frequency will translate to a shorter wavelength and a
smaller patch. Also, using a circuit material with a higher Dk will also
decrease the wavelength and make a smaller patch. As a general statement, the
circuit materials used for PCB-based antenna applications typically have a
lower Dk and commonly have a Dk value in the range of 3-4.
circuit materials with higher Dk will cause the electric fields to concentrate more
between the signal plane and the ground plane of the circuit. The field
concentration will reduce radiated energy and accordingly, PCBs with antenna radiating
elements will often use a material with a relatively low Dk value. Another common
attribute for antenna designs using PCB technology is the use of thicker
laminates. A thicker microstrip circuit will radiate energy better and it is
common for microstrip patch antenna designs to use thicker material (30 mils or
This article is written by John Coonrod. Learn more, please google it.