Millimeter-Wave Slot-Based Cavity Antennas With Flexibly-Chosen Linear Polarization

Slot-based cavity antennas are hailed as promising candidates for millimeter-wave applications. Nevertheless, the linear-polarization (LP) angle of their broadside main beam is limited by the slots etched on the cavity's top surface. In this work, an innovative technique is developed to significantly improve the selection flexibility of their LP inclination angle. It is attained by an integration of a single-layer, closely spaced C-shaped patch surface. A TE 710 -mode slot-based cavity antenna is employed as the base configuration, which radiates a broadside beam with its LP along \phi = 90^{\circ } . To effectively predict and monitor the polarization conversion of the surface-integrated TE 710 -mode cavity antenna, an analysis method using a unit cavity extracted from its original cavity antenna is presented. A subsequent surface-integrated system with the specified 45° LP was then simulated, fabricated, and measured. The measured results validate that a 45° LP state is achieved with an operating bandwidth from 33.3 to 36.5 GHz. Further investigation is conducted to flexibly choose the LP direction from \phi = 15^{\circ } to 165°. Two more examples with the fabricated antenna prototypes successfully radiate the specified \phi = 15^{\circ } and 75° LP beams, respectively. This near-field polarization conversion surface can be generalized to cavities with different resonant modes.