A white paper released by Allen Telecom Group’s Antenna Specialists Division indicates portable users of personal communications services may experience challenges when using a handset inside a vehicle.

“The paper looks at the distortion created by the vehicle at PCS frequencies,” said Dale Horn, author of the paper and vice president of engineering for the Antenna Specialists Division. “This is a whole new experience in terms of a wave length that is a different size.”

The use of PCS handsets, which operate at microwave frequencies, inside an automobile causes the signal to deteriorate and performance suffers because of the shielding effects of the metal car body, said Horn. The only openings in a vehicle are the windows that let the signal out or in. The result is more dropped calls or an increased inability to connect to the network.

“There needs to be an awareness on the part of both the consumer and the service provider only because there is no experience with PCS. The consumer has got to know he’s going to experience differences in performances compared to outside.”

After measuring the performance of a vertically positioned standard half-wave dipole antenna inside a vehicle, the paper, “Portable-Vehicular PCS Antenna Considerations,” concluded the best solution to poor performance is to use an external antenna and/or active mobile repeater positioned inside an automobile with a hardwired external antenna.

“A portable was used inside the vehicle without a driver present because it was too hard to get repeatability with an individual holding a phone in a manner comfortable,” said Horn. “A person doesn’t hold the phone the same way each time. An antenna is generally at an angle-anything except vertical-and that can cause signal loss and a great amount of variability.”

The handset was mounted off the headrest in a position simulating an actual portable antenna. The average signal level from the standard antenna operating inside the vehicle, the paper concluded, is about 5 decibels below the same antenna in free space. “Further, the pattern distortion caused by a passenger operating the phone inside the vehicle increases this loss.”

Using an external-mounted antenna enhances the performance of a handset by providing gain over the antenna on the portable and further improves the signal coverage, Horn continued.

“The good news is that the vehicle’s degrading effect on portable phone performance at PCS frequencies is less than at cellular frequencies, but the efficiency of the portable, plus the relatively small size of the antenna, will result in system performance that is even more user-dependent,” he said.


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