Low Profile Integrated GPS and Cellular Antenna

In recent years, the rapid decrease in size of personal communication devices has lead to the need for more compact antennas. At the same time, expansion of wireless systems has increased the applications for multi-functional antennas that operate over broad frequency bands or multiple independent bands. The civilian GPS system is quickly becoming the standard for personal and commercial navigation and position location. The difficulty with GPS is that there is no return link. That is, a GPS terminal determines its position, but that position is known only to the terminal user. A return link enables positional information derived from GPS to be communicated to a remote location. This is especially desirable for unmanned terminals. The next wide scale technology area for GPS is the integration of a GPS receiver with some type of wireless service to provide communication of the GPS - derived position as well as messaging. One of the most popular uses for this service is tracking of mobile cargo.

This paper presents a design for a compact, low-profile antenna that operates at both the conventional cellular telephone band of 824 to 894 MHz and the civilian GPS L1 frequency of 1575 MHz. The combined antenna unit has a lateral diameter of less than 4 inches (10 cm) and its height is less than 2 inches (5 cm). The integrated unit is a hybrid design of two collocated antennas that operate at the two different bands. The planar inverted F antenna, PIFA, meets the specifications which are required in a reduced size environment. The PIFA is capable of achieving a bandwidth of 8% in the cellular band. The GPS portion of the hybrid unit consists of a dielectrically loaded patch located in a "piggyback" configuration on top of the top PIFA element.

Computer simulation and design were performed using a combination of IE3D, a 2.5 dimensional commercial moment method code, and Fidelity, a commercial full 3D finite difference time domain code. Results will be presented from these calculations along with measurements on prototype antennas using both the Virginia Tech outdoor antenna range and the Virginia Tech near-field antenna range.