Antenna Design

Terminology

Term Description
VSWR VSWR is an initialism for “Voltage Standing Wave Ratio“. The bandwidth of an antenna is usually defined as the range of frequencies at which VSWR is less than 2.

Dipoles

The voltage in a dipole is maximum at the ends, and 0 at the middle. The current is the opposite, with the maximum being in the middle, and being 0 at both ends. The following graph shows this:

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PCB Antennas

You have to consider the placement of other components surrounding the PCB antenna. The following diagram shows the minimum recommended clearances between a PCB antenna and other components.

typical-minimum-component-clearances-from-pcb-antenna The minimum recommended clearances between a PCB antenna and other components. Image from http://www.antenova-m2m.com/resources/literature.

Shorting Antennas

Note that shorting out an antenna is not an effective way of stopping it from communicating. At RF frequencies, a direct short with a piece of wire is no longer a direct short, and can for example, appear inductive. This means the antenna can still work, and sometime make it perform better! I have shorted out cellular modem antennas before with pliers and the signal strength increased!