Wideband Substrate Integrated Magneto-Electric Dipole Antenna Arrays


Student thesis: Doctoral Thesis

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Award date19 Aug 2021


This thesis presents a series of wideband substrate integrated antennas and arrays. All the proposed antennas are based on the concept of magneto-electric (ME) dipole and are extended to arrays for practical applications, including low side lobe level (SLL), compactness for beam scanning, low-profile reconfigurable transmitarray, and the dual-polarizations. The proposed antennas are developed based on the concept of ME dipole, which enables to maintain good performance over a wide operating frequency band. Moreover, the proposed antenna arrays are integrated into the substrates, demonstrating their ease of integration with other systems, and fabrication-friendly nature. 

First, a new method is proposed to suppress the SLL of the antenna array. Different from conventional amplitude-tapered excitation methods, ‘±1’ excitations are used to feed the antenna array and achieve low SLL. The SLL performance can be optimized by using a modified binary particle swarm optimization (MBPSO) algorithm with ideal ‘±1’ excitations. Then, the ideal ‘±1’ excitations are replaced with microstrip line feed and aperture coupled ME dipoles. The ‘+1’ excited ME dipoles are fed from the default direction, while the ‘−1’ excited ME dipoles are fed from the direction physically reversed. According to the optimized array configuration, combining the ME dipole elements with a 256-way parallel power divider, a planar 16 × 16 millimeter-wave antenna array is designed, fabricated, and measured. An overlapped operating bandwidth of 38% (24.1−35.4 GHz) is obtained with an SWR less than 2.4 and an SLL lower than −17.2 dB. The gain is up to 26.3 dBi. The new binary concept paves a new way for SLL suppression.

Second, a wideband compact ME dipole antenna is investigated for millimeter-wave beamforming applications. An ME dipole fed by a substrate integrated coaxial line (SICL) is proposed, with a wide operating frequency band and low profile. Then, transverse slots are etched on the patches to miniaturize the antenna. The radiation performance of the higher-order mode is also improved. The antenna is finally miniaturized to 2.5 × 3.3 mm2 (0.27 λ0 × 0.35 λ0, where λ0 is the wavelength in free space at the center frequency) in an array environment. A bandwidth of 48.8% (24.3−40 GHz) for SWR < 2 can be achieved, with a unidirectional radiation performance over the operating band. By combining the proposed compact antenna with an 8-way SICL feed network, a 1 × 8 linear array is designed, fabricated, and measured. Due to the compact size of the antenna, a beam-scanning potential of ±45° can be achieved over a wide frequency band. 

Third, a wideband 1-bit reconfigurable transmitarray (RTA) with a low-profile characteristic is presented. First, a wideband element of the RTA is designed by combining two central-via-feed ME dipoles, and two pin diodes are integrated within the element to achieve 1-bit reconfigurable phase states. Next, the folded scheme is adopted to achieve multiple reflections between the feed source and the RTA, this reduces the focus-to-diameter ratio (F/D) to about one-third of the conventional transmitarray. A reflective surface with a polarization conversion function is designed beneath the RTA around the source, the unit cell of which is a special C-shaped polarizer operating over a wide frequency band. Finally, a prototyped low-profile RTA with 12 × 12 elements is designed, fabricated, and measured. The whole structure has an aperture size of 5.75λ0 × 5.75λ0, and the height-to-diameter ratio (H/D) is 0.28. The measurement results show that the proposed RTA has a beam-scanning capability to ±40° in both E- and H-plane throughout a bandwidth of 32%. The realized gain is up to 19 dBi and the peak aperture efficiency is 20.5%.

Finally, a wideband dual-polarized ME dipole for millimeter-wave applications is presented. The ME dipole consists of four shorted patches, which are fed by two pairs of T-shaped probes orthogonally oriented on the same layer. The feed lines are connected with the T-shaped probes through metallic vias. A simulated overlapped impedance bandwidth of 50% is achieved with return loss larger than 10 dB, gain up to 9.4 dBi, and isolation higher than 17.8 dB between the dual polarizations. By combining the antenna elements with single-layered feed networks, a 2 × 2 array is designed, fabricated and measured. The overlapped operating bandwidth is 50%, respectively, with a gain of up to 14.8 dBi.