Design of wideband and dual-band antennas for 5G and sub-THz 6G wireless communication systems

This thesis presents various methods to design wideband antennas with multi-mode operation for millimeter wave (mm-Wave) and sub-THz applications. To start with, a tri-mode magneto-electric (ME) dipole antenna for the fifth generation (5G) communication system is presented, covering 5G New Radio FR2 bands of 24.25–29.5 GHz and 37–40 GHz. The proposed antenna is designed systematically using characteristic mode analysis (CMA), which provides insights into each individual resonant mode. This systematic design method facilitates the design process and reduces the optimization effort. Furthermore, each resonant mode can be manipulated independently. Likewise, a wideband low-profile wristband ME dipole antenna with unidirectional radiation property is designed in a similar way using CMA. Alternatively, a wideband antenna for sub-THz detector application is implemented by combining the fundamental mode and the first higher order mode. To move the resonant frequency of the higher order mode of this dual-mode antenna towards the fundamental resonance, a stepped-impedance structure is introduced into the dual-folded-dipole antenna to control the frequency ratio of two modes.

Developed from the above mentioned tri-mode ME dipole, a dual-wideband dual-polarized antenna is proposed to cover FR2 bands of 24.25–29.5 GHz and 37–43.5 GHz with second-order bandstop filtering characteristics. The band-notched behavior with high band-edge selectivity is implemented by two types of resonators, namely hairpin and coupled λ/4 open-/short-circuited stub resonators. Moreover, without increasing the size of the reference wideband antenna, the proposed dual-wideband antenna provides independent control of the transmission poles and zeros.

To compensate for the free space loss at mm-Wave and sub-THz frequencies, an integrated lens antenna is adopted. Furthermore, more feed elements at the focal plane can be activated to enhance the effective isotropic radiated power (EIRP) of the antenna system. A technique that uses conjugate field matching to predict the complex excitation coefficient of array elements of a feed cluster at the focal plane is proposed. This method improves the scanning properties, e.g. sidelobe level, directivity, and aperture efficiency for both the two-element and five-element design cases. Instead of activating several array elements at the focal plane, an alternative method, say in-antenna power combining with multi-feed leaky slot antenna structure, is presented.