RADIO PHYSICS AND RADIO ASTRONOMY

Subject and Purpose. Essentials of the processes for millimeter-wavelength radiation from circular apertures are analyzed, with emphasis on the formation of the field’s radiation pattern (RP) and modal structure in the aperture. The work is aimed at obtaining analytical expressions for the circular aperture’s RP and verifying these in experiments. Further aims include investi- gation of radiation characteristics and possibilities for forming up specific types of wave beams for applications like medicine, communications and interaction with aerial vehicles. Also, possible techniques of Bessel beam generation are investigated for the millimeter-wavelength range.

Methods and Methodology. The electromagnetic field distribution over the waveguide aperture is assumed to be available for determining its radiated field in free space. The far-field characteristics are calculated via Kirchhoff ’s integral taken over the aperture and verified experimentally by measuring the RP and the voltage standing wave ratio (VSWR) in the wave guiding channel.

Results. Explicit expressions for the RP of a circular aperture have been derived, with the use of pattern functions, for two mutually orthogonal planes. Measurements at a frequency of 34 GHz revealed that a circular aperture of a 30 mm diameter provided for a voltage standing wave ratio (VSWR) in the guiding channel close to 1.0558. The calculated and measured cross section areas of the RP, as estimated for the planes of the E  and H field vectors, coincide with a Gaussian distribution to the level of −8.7 dB. The RPs produced by apertures of circular and rectangular cross-sections have been compared for antennas of equal maximum sizes.

Conclusions. Analytical expressions have been derived for the radiation pattern (RP) of a circular aperture supporting the TE11 mode in two mutually orthogonal planes. As has been found, such an aperture cannot provide for formation of the far- field electric distribution required for generating a Bessel wave beam at the conical lenses’ output.

Keywords: aperture method, millimeter wavelength range, circular aperture, radiation pattern, Gaussian distribution, voltage standing wave ratio (VSWR), conical lens

Manuscript submitted 16.03.2026

Radio phys. radio astron. 2026, 31(2): 108-118

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