NEW VOR COUNTERPOISE SYSTEM FOR REDUCTION OF SITING ERRORS.

The analysis of the field pattern generated by an Alford loop above a circular counterpoise is treated quite effectively by replacing the fields of the Alford loop by those of a nearly equivalent circular loop, this being justifiable upon consideration of the frequency and dimension parameters involved. A detailed theoretical analysis results in an expression for the free space field pattern of a circular loop above a large counterpoise as a function of the following parameters wavelength of transmitted energy, height of loop above counterpoise, and size of counterpoise. The expression holds for counterpoise, diameters large compared to wavelength. Experimental verification of field patterns was possible for all single and double loop configurations under consideration, including both small and large diameter counterpoise. The antenna elements employed were actual scaled versions of the operational Alford loops. Precautions in measurement technique, such as placement of microwave absorbant material were vital to obtaining good nulls in the multiple loop patterns. The multiple loop patterns present significant improvement in essential radiation characteristics over the single loop configuration and it is therefore felt that serious consideration should be given to use of the multiple loop configuration as a means of eliminating VOR bearing errors in areas containing undesirable geographic and man-made characteristics.