Personal radio antennas

Abstract

The trend toward personalizing vehicular radio sets has been accompanied by major engineering problems. Of these, one of the most challenging is that of designing an efficient antenna to occupy a small space. Due to these size limitations, personal radio antennas will be referred to as small antennas. This paper will describe a series of tests made under laboratory conditions followed by a coverage study made under service conditions in city streets to evaluate the relative performance of small antennas and accumulate propagation data for system design. The laboratory measurements included a study of the properties of ferrite loop antennas, coils, whips and short wire antennas. The field measurements covered actual recorded field strength data from personal carried transmitters using reference quarter-wave whips. It was concluded that ¾-wave whips even when working against as poor a ground plane as the set chassis offered the best performance. However, the 20 to 25 db of shadow loss found in city streets plus a 10 to 15 db antenna loss even with whips will severely restrict the coverage of personal transmitters. Other steps may be necessary if adequate areas are to be reliably covered.