Printed Loop Antenna with Four Resonant Modes
Image of the Printed Loop Antenna with Four Resonant Modes.

The need for multiband antennas to cover various bands like GSM/LTE, WiFi, GPS etc. is constantly increasing. While PIFA/IFA antennas are very popular, their unbalanced modes have high ground plane surface currents which makes them sensitive to user interaction. The balanced modes of loop antennas on the other hand have less surface currents, making them more suitable for user interaction. Unfortuantely, these balanced modes lead to structures with smaller bandwidths than those of conventional PIFAs/IFAs.

The four mode loop antenna has four resonant modes. These modes are generated by the folded, meandered loop element. The bandwidth of the lowest mode can be increased by using a matching circuit, while the others are increased by adjusting the tuning arms or adjusting the spacing between the feed and shorting pins.

Typical total gain at fmin, 2.17fmin and 3.8fmin
Reflection coefficient in dB versus frequency overlaid with popular LTE bands