MCML-BF: A Metal-Column Embedded Microstrip Line Transmission Structure with Bias Feeders for Beam-Scanning Leakage Antenna Design

Abstract

This article proposes a novel fixed-frequency beam scanning leakage antenna based on a liquid crystal metamaterial (LCM) and adopting a metal column embedded microstrip line (MCML) transmission structure. Based on the microstrip line (ML) transmission structure, it was observed that by adding two rows of metal columns in the dielectric substrate, electromagnetic waves can be more effectively transmitted to reduce dissipation, and attenuation loss can be lowered to improve energy radiation efficiency. This antenna couples TEM mode electromagnetic waves into free space by periodically arranging 72 complementary split ring resonators (CSRRs). The LC layer is encapsulated in the transmission medium between the ML and the metal grounding plate. The simulation results show that the antenna can achieve a 106° continuous beam turning from reverse -52° to forward 54° at a frequency of 38 GHz with the holographic principle. In practical applications, beam scanning is achieved by applying a DC bias voltage to the LC layer to adjust the LC dielectric constant. We designed a sector-blocking bias feeder structure to minimize the impact of RF signals on the DC source and avoid the effect of DC bias on antenna radiation. Further comparative experiments revealed that the bias feeder can significantly diminish the influence between the two sources, thereby reducing the impact of bias voltage introduced by LC layer feeding on antenna performance. Compared with existing approaches, the antenna array simultaneously combines the advantages of high frequency band, high gain, wide beam scanning range, and low loss.

Keywords: beam scanning; bias feeder; holographic principle; liquid crystal; periodic leakage antenna.

Figure 1

The antenna cell structure. (a) Main view; (b) Top view; (c) left view.

Figure 2

Electric and magnetic field energy distribution at the CSRR slot. (a) Electric field energy distribution; (b) Magnetic field energy distribution.

Figure 3

Comparison of MCML and ML performance after removing the CSRR slot. (a) S₁₁ parameters; (b) S₂₁ parameters.

Figure 4

Comparison of electromagnetic wave transmission between MCML and ML structures. (a) ML electric field energy map; (b) MCML electric field energy map; (c) ML electric field vector map; (d) MCML electric field vector map.

Figure 5

MCML cell performance simulation. (a) S₁₁ parameters; (b) S₂₁ parameters.

Figure 6

Dispersion curve of antenna unit.

Figure 7

Radiation diagrams of MCML cell. (a) 3D plot; (b) 2D plot.

Figure 8

Structure of the periodic leakage antenna array.

Figure 9

Beam gain maps corresponding to different beam directions.

Figure 10

Reflection coefficients corresponding to different beam directions.

Figure 11

Bias feeder structure.

Figure 12

Comparison curves of S₃₁ parameters under different w_bias values.

Figure 13

Comparison curves of S₃₁ parameters under different d_bias values.

Figure 14

Sector-blocking bias feeder structure.

Figure 15

Comparison curves of S₃₁ parameters under different d_sec and r_sec values. (a) d_sec; (b) r_sec.

Figure 16

Beam gain diagrams corresponding to different beam directions after adding bias feeder.

Figure 17

Reflection coefficients corresponding to different beam directions after adding bias feeder.