Band-stop filter effect of multiple slots in mobile phone antennas

A slot placed between the feed and the ground connections of a single shorted microstrip antenna in a two antenna system can produce a band-stop filter effect in one of the frequency bands where both antennas radiate at the same frequency. This band-stop filter effect creates a large group delay at a particular frequency anti-resonance and depends on the slot parameters and the feed/ground placement relative to the second antenna. This paper will show that a second slot can produce an additional band-stop anti-resonance to create two bandstop frequencies. The antenna geometry analyzed is a two planar inverted-F antenna system inside a mobile device where the first antenna with slots has both lower band and high band resonances (quad-band GSM or dual-band LTE) and the second antenna is a wide-band single frequency antenna at LTE/3G/WiMAX.