A Novel Impedance Matched Mode Generator for Excitation of the TE21 Mode in Compact Dual-Mode Circular Waveguide Feeds

作者：Pour Z Allahgholi^*; Shafai Lot

来源：IEEE Antennas and Wireless Propagation Letters, 2011, 10: 427-430.

DOI：10.1109/LAWP.2011.2153819

• Circular waveguide
• compact size
• dual-mode feed
• input impedance

A compact dual-mode circular waveguide horn antenna is presented that is fed by the dominant TE11 mode and generates the higher-order TE21 mode in order to reduce the cross polarization of offset reflectors. To excite the second mode, two blocks and a small discontinuity step are used. These blocks are tangent to the aperture of the second waveguide, as opposed to the traditional case where they are usually located right at the discontinuity step, which results in high reflections. An analytic model is then deployed to extract the mode content factor along with the field tapers of each mode in the principal planes. Other than far-field radiation patterns, emphasis is placed on the scattering parameters of the antenna, and they are compared to the ones for the same antenna with no blocks as well as the traditional case when the blocks are placed right at the discontinuity of the stepped waveguide. It is shown that the proposed feed provides a good impedance match, over a wide frequency band, similar to its counterpart for the single-mode antenna with no blocks. To verify the concept, a prototype antenna is fabricated and tested. There is an excellent agreement between the simulated and measured results.

• 出版日期2011