A wide-band electromagnetic coupler for thru-glass applications

Externally mounted cellular antennas are often used in cars in conjunction with a phone handset. External antennas not only improve antenna system performance but also decrease radiation exposure to the phone user. The antennas for cellular phones can be roof-mounted, magnetically mounted or mounted on the glass of the vehicle. The glass-mounted antenna offers distinct advantages in that a hole does not need to be punched or drilled in the sheet metal of the vehicle nor does a cable have to be routed through a window or body panel opening. This paper presents a new geometry for the efficient coupling of multiple cellular bands (North American AMPS/PCS or European GSM/PCS/UMTS) through automotive glass. The new coupling geometry is of a small size and has a bandwidth on the order of 100% based on a 3 dB reduction from the peak coupling frequency. Dimensions of the coupler can easily be changed to shift the coupling response up or down in frequency. The frequency bands covered lie between 824 MHz and 2.17 GHz.