Digital Microwave Radio Program

In 1981 CECOM placed four contracts for the exploratory development of ECCM techniques which are to be considered for use in a new digital microwave radio development. A spread spectrum modem is under development which will operate in the 4.4 to 5.0 GHz band. The modem will also be designed to operate, with minor changes, in the 14.4 to 15.35 GHz range. The modulation techniuqe selected is offset quadriphase shift keying. A hybrid direct sequence/frequency hopping system is being designed. The data rates at which the modems are expected to operate are related to various TRI-TAC and DCS multiplexers. Input data rates will vary from 72 kbps to 4.608 in the 4.4-5.0 GHz band and from 72 kbps to 18.720 Mbps in the 14.4-15.35 GHz band. The modulation and frequency translation schemes will be discussed. A steerable null antenna system will be designed for both RF bands and fabricated for C-band. The objective of this antenna is to discriminate against unwanted signals arriving in its side lobes and in the main beam. Among the requirements and constraints which will affect the antenna design are the need for duplex operation, the necessity for installation of the antenna on a 100 foot tactical mast, and the requirement to operate with high output power levels. A coding equipment development is underway which will result in the fabrication of an error correction technique to correct random errors and bursts of errors in the modem output.