Suppression of Undesired Radiation of Directional HF Antennas and Associated Feed Lines

An analysis of the situation in point-to-point radio communication circuits at frequencies below MUF with respect to radiation in undesired directions brings to the fore some aspects which are useful as guide lines in antenna research, design, and application engineering. In many cases, the interference experienced in operating receivers in the high-frequency range can be attributed primarily to the relatively high side lobes of the radiation pattern of rhombic antennas. Progress has been made in suppressing these side lobes through the development of antenna arrays employing nonuniform amplitude distributions and, more recently, through the advent of modified horn-type antennas. Other sources of interference which are usually overlooked are associated with balanced open-wire lines which are not operated properly. Recently, it has become feasible to replace these lines by coaxial cable using broad-band balun transformers.