LOW ENERGY MICROWAVE AUTOMATIC COMMUNICATIONS SYSTEMS (LEMACS). SECOND INTERNATIONAL CONFERENCE ON ROAD TRAFFIC MONITORING

This article describes a low energy microwave automatic communications system designed to satisfy the requirements of non-stop toll collection. This system is based on a duplex two-way microwave data-communications system between the moving vehicle and a roadside vehicle incorporating a low profile vehicle mounted receiver unit. Data is transmitted on a frequency of 2.45 ghz, with a power output restricted to +5 dbm. Physical size and power are very important and a small low profile transponder card about the size of a credit card with its own internal power supply are used, utilizing microstrip technology. Details of circuit design are provided. Three methods of data retransmission are discussed (local oscillator, frequency doubler razban, and frequency re-use). Details of method of transmission used by the roadside beacon, and design details of the transponder/roadside beacon, its antenna and its microprocessing unit are also provided. (TRRL)