Microwave Repeater Research

Microwave Repeater Research m INTRODUCTION m TT WAS some 80 years ago that Maxwell and Hertz demonstrated that free space is a good transmission medium for electromagnetic waves. Since this fundamental contribution, the radio art has advanced tremendously and a decade ago it had progressed to the point where it was possible to construct equipment suitable for quantitative propagation studies of microwaves. Such studies were made and they indicated that normal propagation over "line-of-sight" paths of signals of 10 to 20 centimeters wavelength was characterized by free space attenuation and freedom from atmospheric interference. These results, together with the facts that in this wavelength range wide bands of frequencies are available and it is possible to design small antennas having high directivity, encouraged us to start more comprehensive research work on microwave repeater circuits. This paper gives the present status of the work which was interrupted by our war efforts and resumed at the end of the war with the construction of an experimental New York-Boston system as an initial objective. The first section will describe our propagation studies. It will be followed by sections on repeater circuit planning, antennas, radio frequency channel filters, the construction and testing of the repeater amplifier, and a concluding section on the whole repeater. I. PROPAGATION STUDIES* By H. T. FRIIS That portion of the radio frequency spectrum represented by wavelengths shorter than about five meters has long been considered as the proper domain for point-to-point communication links, local broadcasting, and mobile radio communication.