$4\times8$ Patch Array-Fed FR4-Based Transmit Array Antennas for Affordable and Reliable 5G Beam Steering

Abstract

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.

Beam-Steerable Passive Transmitarray Optimized Based on an Adjacent Algorithm

“…In addition, there was a gain improvement greater than 1 dBi compared to the TA optimized at 0° with a beam-steering angle of about 23° at a PO of 75°, and the gain improvement was 5 dBi compared to when only the feed antenna was used. In order to compare this with an account of gain improvement efficiency in the literature [10], the relationship between the aperture efficiency and the antenna gain was used [20]. The calculated gain improvement efficiency in one earlier study [10] was 0.0005, while that in the present paper is 0.0167, representing an improvement of approximately 27 times.…”

“…However, for simulations using unit cells, designing the unit cells requires a considerable amount of time, and errors can occur because each unit cell has different transmission losses. Therefore, an effective simple medium was used instead of unit cells to save time and to ensure that the gains of various beam-steering directions are actually improved [10]. After optimizing the POs of the feed antenna at 0° and 75°, the phase change of the passive TA was determined by (3), and the gain improvement of the optimized case was ensured using an effective medium instead of unit cells by ANSYS HFSS.…”

“…The thickness of the effective medium structure was selected to be 2.5 mm and the lateral dimension of the unit cell was 2.5 mm. The TA design follows the procedure described in the literature [10]. The potential design of TA using unit cells based on the state of art is depicted in Figure 17.…”

“…Nevertheless, the conventional passive transmitarray (TA) or lens was only designed to enhance the gain in the boresight direction [6][7][8][9]. If unit cells are arranged using the phase distribution on a TA based on the beam of the feed antenna in the direction of the boresight, the gain improvement is smaller in the remaining directions apart from the boresight direction [7], [10]. Some studies have shown different unit cell layouts that are robust to beam steering in a feed antenna to compensate for the gain reduction [10], but different beam- steering angles were not considered.…”

“…If unit cells are arranged using the phase distribution on a TA based on the beam of the feed antenna in the direction of the boresight, the gain improvement is smaller in the remaining directions apart from the boresight direction [7], [10]. Some studies have shown different unit cell layouts that are robust to beam steering in a feed antenna to compensate for the gain reduction [10], but different beam- steering angles were not considered. The beam-steering feature can be achieved by employing active components or active materials such as varactors, pin diodes, and liquid crystal in antennas [11][12][13], especially in reflectarray (RA) antennas and TA antennas for beam steering.…”