case. The beamwidth is inversely proportional to the directivity. It can be noted that the cross-polarization pattern can be divided into two ranges. One range is within the main beam and the other is beyond the main beam. Within the main-beam range, the crosspolarization level increases as the directivity increases, as shown in Figure 9.
3. EXPERIMENTAL RESULTS
Two antennas are built with two different waveguide types, as shown in Figure 10. The first antenna is made with a circular waveguide and the second antenna with a rectangular waveguide. The flanges are square shaped, which destroys the axial symmetry. The first antenna has flange dimensions of 58 Ο« 58 mm, waveguide diameter of 22 mm, a squired dielectric slab of 30 Ο« 30 mm, and thickness 2.54 mm; the distance between the waveguide aperture and the dielectric slab is 15 mm; and r Ο 10.2. The measured radiation patterns at 10 GHz are shown in Figures 11(a) and 11(b), without and with dielectric slab, respectively. The second antenna has a rectangular waveguide aperture of dimensions 22.86 Ο« 10.16 and flange dimensions 41 Ο« 41 mm, a squired dielectric slab of 30 Ο« 30 mm, and thickness 2.54 mm; the distance between the waveguide aperture and the dielectric slab is 15 mm; and r Ο 10.2. The radiation patterns without and with the dielectric disc are shown in Figures 12(a) and 12(b), respectively. It can be seen that the beamwidth of the antenna with the dielectric slab is much narrower than the beamwidth without the dielectric slab, regardless of the radiating-aperture shape.
4. CONCLUSION
In this paper, placing a dielectric disc in front of its aperture has enhanced the directivity of a circular waveguide with flange. The effect of different parameters on the directivity, phase center, and cross-polarization was investigated. The concept was also verified experimentally and showed that the dielectric slab will enhance the antenna directivity, regardless of the aperture shape, as was demonstrated experimentally.