Biaxial beam reconfiguration of flat slot antenna array using reconfigurable synthesis transmission line

Journal:
IEEE Transactions on Antennas and Propagation

IF: 4.388 (2021)

DOI:
10.1109/TAP.2017.2700235

Keywords:
Impedance, Microstrip antenna arrays, Switches, Feeds, Microstrip, Varactors, Slot antennas

Beamwidth Switchable Planar Microstrip Series-Fed Slot Array Using Reconfigurable Synthesized Transmission Lines

Huy Nam Chu, Tzyh-Ghuang Ma

Dr. Chu Huy Nam, MediaTek Inc., Hsinchu, Taiwan

Reconfiguring the beam for the antenna array can help increase anti-interference ability and increase coverage by controlling the direction of radiation. While the old methods of applying mechanical control encountered many difficulties in terms of vibration during the reconfiguration process as well as the reconfiguration time being too slow. Recent approaches using radio frequency (RF) on/off switches such as PIN diodes or MEM micromechanical switches offer convenience and shorten reconfiguration time. However, MEM switches require very high precision in manufacturing and quite high voltages to achieve good performance, which makes it difficult to maintain and supply voltage to the reconfigurable system. image. In contrast, diode PIN switches, although simpler in terms of voltage supply, consume too much power to be effective (low loss, high isolation). This causes inadequacies in designs for mobile phones or handheld devices due to limited power supply.

This article presents the idea of a reconfigurable synthetic transmission line to replace RF switches while still ensuring the desired effects and especially the almost negligible power consumption. The idea comes from using variable diodes combined with concentrator elements to create a perfect on/off circuit for a predetermined frequency. The efficiency of the reconfigurable synthesis line is completely comparable (or superior) to common RF switches on the market. In particular, the use of variable diodes in the reverse voltage region almost does not allow direct current to pass through. This minimizes the power consumption of the synthesis link, which can provide high efficiency at RF frequencies. Based on Figure 1, when operating in the open state (Figure 1b), the resonator L₃C_eq (C_eq is the equivalent capacitance of the structure L₂C_v) acts as an ideal open-circuit structure circuit. This makes the remainder of the composite transmission line equivalent to an ideal microstrip transmission line with low loss and reflection coefficient. On the contrary, when operating in the closed state (Figure 1b), the circuit resonates L₂C_v,off creates a short-circuit structure that prevents the signal from passing through the output. By adjusting the remaining parameters of the circuit (L₁, C₁, q1) we can tune the input impedance of the composite transmission line close to an ideal open circuit structure with a very high reflection coefficient.

To demonstrate the applicability of the above idea, a reconfigurable synthesis line was designed and integrated into the slot antenna array to be able to steer the beam along two axes. x and y. Controlling the number of radiating elements in the two axes results in the beam and gain of the slot antenna array being flexibly controlled.

By integrating the reconfigurable synthesis line into the slot antenna array as shown in Figure 2 to replace the RF switches (S1 and S2), the number of radiating elements (indicated by dark dots) can be adjusted. controlled in three modes (3×6, 2×4, and 1×2). The parameters of the antenna array such as gain, emission efficiency, and reflection coefficient all show positive results. When compared with reconfigured antenna arrays using old methods such as mechanical control or RF switches, the proposed antenna arrays show advantages such as vibration resistance (compared with mechanical control) or save energy (compared with RF switch control).