Tech Papers and Guides

Electrically-short antennas

Electrically-short (E-field) antennas are a fraction of a wavelength (typically ≤ l/4) with a single-ended, un-balanced structure. Unlike a connectorized l/4 monopole antenna, these structures are not typically mounted perpendicular to a conducting ground plane. Therefore, be careful when you select one, the PCB layout, and how you tune the device.

The electrically short antenna structure lends itself well to sensor applications; they are typically low-cost and often good for space-constrained designs.

The lowest cost antenna is the PCB trace antenna, such as a meander line, Inverted F antenna (IFA) and Meander Inverted F antenna (MIFA). If an application is not space-constrained, use a wire antenna. If the PCB area is limited, use embedded chip antennas. These are available from multiple vendors, many of whom offer both PCB and layout recommendations, as well as design optimization services. Ultimately, the antenna you should select depends on the application requirements.

Compare common electrically-short antennas on a scale of one to five, where one is the worst relative performance and five is the best:

Antenna type

Rel. gain

Size

Cost

De-tuning immunity

Notes

Monopole

5

1

1

4

Perpendicular ground for opt. results

Wire

4

1

4

3

 

PCB antenna

3

2

5

3

IFA and MIFA structures can require large area

Helical antenna

3

4

1

1

Add counterpoise to improve de-tuning

Chip

1

5

2

2

Vendors provide detailed guidance

Table 1: Electrically-short antenna relative performance