MICROWAVE REPEATER RESEARCH 201 



An increase in the effective area, A, of the antennas reduces both the total 

 gain required of the amplifier and the output noise power. Crosstalk be- 

 tween the several antennas in a repeater station and interference from outside 

 sources also decrease as the antennas are increased in size because of the 

 increased directivity. Therefore, the antennas should be as large as main- 

 tenance and initial costs will permit. Antennas will be discussed in detail 

 in Section III. 



Equations (II-2) and (II-3) show that the wavelength X should be small. 

 Also more frequency space or signal channels may be had at shorter wave- 

 lengths. On the other hand, the fading factor M increases somewhat as the 

 wavelength is decreased and, besides, attenuation due to rain sets a lower 

 limit for X in the region of 5 centimeters. The status of the apparatus art has 

 also been an important factor, but it now permits utilization of the wave- 

 length range extending upward from 3 centimeters. Since the war, our work 

 has been concentrated on a 10% band around 4000 megacycles or 7^ 

 centimeter wavelength. The manner in which this 4000-megacycle band 

 may be divided up into separate channels is explained in Section IV. 



The effects of varying the repeater separation d will now be discussed. 

 d appears in the denominator of the exponent of (IT2) which indicates that 

 large separations are favorable, while (II-3) shows that a decrease in separa- 

 tion cuts down the noise. Small separations are very costly, the cost being 

 almost inversely proportional to the separation. We have concluded from 

 propagation studies and site surveys that in the eastern part of the United 

 States it is desirable to use separations of about 30 miles, which generally 

 provide line-of-sight paths with reasonable tower heights. It should be 

 mentioned that the fading allowance factor M is not independent of d; 

 an increased d requires a larger fading factor. 



III. Antenna Research* 



There are three electrical characteristics which repeater antennas should 

 possess. The first is high gain (large effective area), as this will reduce the 

 path loss and accordingly the requirements on transmitter power. The 

 second is good directional quahties so as to minimize interference from out- 

 side sources and also interference between adjacent antennas. The third 

 is a good impedance match so that reflections between the antenna and the 

 repeater equipment will not distort the transmitted signals. These char- 

 acteristics should preferably be attainable without the imposition of severe 

 mechanical or constructional requirements. 



It was felt that a 10-foot round or square antenna would be the largest 

 that maintenance and initial cost would permit. Propagation studies also 



* This section prepared by W. E. Kock who performed the major part of the work on 

 antennas. 



