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This paper presents a novel method of designing affordable 28-GHz transmit array antennas utilizing FR4 substrates, which are low-cost but lossy. It is demonstrated that low insertion loss can be achieved by employing appropriate combinations of spatial filter unit cells, where each unit cell is selected to minimize the loss factors defined by lossy spatial filter modeling. The loss factor with inter-layer couplings was found to be more variable than that without inter-layer couplings, although inter-layer couplings have previously been utilized to increase the tunable range of the phase shift. Therefore, the number of metal layers in the low-pass spatial filter more affected by the inter-layer coupling is selected to be less than the number of metal layers used in the bandpass spatial filter for a given thickness in the proposed method. In addition, a novel transmits array in which some of the unit cells are sinusoidally arranged is described. This can achieve up to 1.6-dB gain enhancement at some steered angles compared with the conventional design. To simulate transmit arrays rapidly, an effective simple medium structure representing a transmit array is presented. Finally, the measured results confirm the effectiveness of the proposed design approaches for affordable transmit array antennas. Only a small difference of 0.8 dB between the simulated and measured results confirms the successful manipulation of the lossy characteristic of FR4.

This paper describes a millimeter-wave thin lens that exhibits different beam-shaping characteristics depending on the polarization of the incident waves. The proposed unit cell topologies, which use multiple rectangular patches and rectangular-slotted grids, enable thinner (= 0.05λ 0) and smaller (= 0.168λ 0) features than in previous polarization-dependent lenses. An appropriate set of the proposed unit cells is shown to cover a tunable phase range of 180 • with respect to one polarized wave but have an almost-zero tunable range of phase shifts with respect to another polarized wave. Thus, using this unit cell set for x-polarized incident waves, the proposed lens operates as a convex lens, whereas for ypolarized incident waves, the lens operates as a frequency selective surface. This confirms that gain variations of 13 dB or more can be differentiated according to the polarization of the incident waves on the lens, supporting polarization-dependent beam-shaping capability as a function of the polarization of incident waves.

This paper presents a new accurate and efficient design methodology for complex integrated lens antenna (ILA), to achieve wide-angle beam coverage with scan loss mitigation at the millimeter-wave (mmWave) spectrum. The proposed ILA comprises inhomogeneous curvatures with internal and external center off-sets, in which multiple parameters instigate high order and non-linear behaviors. A two-dimensional (2-D) ray-tracing model is used to estimate the refractions on the elliptically curved boundaries based on geometrical optics. This approach is integrated into the particle swarm optimization of the 2-D raytracing model to determine the near-optimum geometric configuration of the ILA. Denoted as Geometric Optics-based Multiple Scattering (GOMS), the computational memory usage is reduced by a factor of 10,000 using this approach. The devised ILA achieves a wide-angle beam coverage of 156 ° with a scan loss of 2.10 dB alongside a broad impedance bandwidth of 35.0 GHz to 42.0 GHz. The measurement results for the performance of the fabricated prototype of the ILA validate the wide-angle scanning with scan loss mitigation inferred from the simulation results. This confirms the effectiveness of this method for complex design challenges involving multi-variants and restricted computational resources.

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