CIRCUIT DESIGN
Antenna Design
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Overview
Antennas are an import part of any circuit design which incorporates RF frequencies.
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.
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.
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!
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