Meandering microstrip leaky-wave antenna with dual-band linear-circular polarization and suppressed open stopband

TL;DR

The paper tackles the challenge of achieving dual-band, polarization-controlled beam scanning in a compact, conformal mm-wave antenna. It proposes a time-delay-based, three-meander unit cell augmented with two smaller meanders to realize dual-band operation via spatial harmonics $n=-1$ (Ku-band, LP) and $n=-2$ (K-band, CP), while suppressing open stopband through mitered corners. The approach is supported by analytical design relations, Brillouin diagrams, and full-wave simulations, and is validated experimentally in K-band and Ku-band, showing broad scanning ranges and polarization performance. The design remains vias-free and compatible with flexible substrates, with practical guidance for OSB mitigation and Ku-band efficiency enhancement through substrate thickness or extended cascades.

Abstract

This paper proposes a dual-band frequency scanning meandering microstrip leaky-wave antenna with linear polarization in the Ku-band and circular polarization in the K-band. This is achieved by making use of two spatial harmonics for radiation. The unit cell of the periodic microstrip antenna contains three meanders with mitred corners. To ensure circular polarization, a theoretical formulation is developed taking into account the delay caused by microstrip length intervals. It defines the unit cell geometry by determining the length of the meanders to ensure that axial ratio remains below 3 dB throughout the operational band. Moreover, the meanders are used to provide better control over scanning rate (the ratio of change of angle of maximum radiation with frequency) and reduce spurious radiation of harmonics by ensuring single harmonic operation within the operational band. To guarantee continuous scanning through broadside direction, open stopband is suppressed using mitered angles. The antenna is designed on a 0.254-mm substrate making it suitable for conformal applications. The fabricated antenna shows a backward to forward beam steering range of 72 deg (-42 deg to 30 deg) in the K-band (19.4-27.5 GHz) with circular polarization and of 75 deg (-15 deg to 60 deg) in the Ku-band (11-15.5 GHz) with linear polarization.

Figures (16)

• Figure 1: (a) Configuration of the proposed 10 unit cells periodic frequency scanning antenna with radiation pattern shown in the broadside direction. The meandering microstrip is etched on top layer while bottom layer is copper. (b) Beam scanning operation of the proposed LWA as a function of frequency in the Ku-band and K-band. The antenna radiates a fan-beam in the E-plane (X--Z plane), while in the H-plane (Y--Z plane) the antenna changes the direction of maximum radiation with change in frequency.
• Figure 2: Evolution towards final design of proposed unit cell: (a) conventional unit cell operating in single band and radiating due to the $n=-1$ spatial harmonic, (b) dual band operating unit cell radiating due to $n=-1$ and $n=-2$ spatial harmonics, and (c) modified unit cell with the introduction of two meanders ($p<p_0$) to improve the scanning range and the circular polarization performance.
• Figure 3: $E_{\mathrm{abs}}$ plots at phase 0° for the frequency at which broadside radiation occurs for (a) $n=-1$ and (b) $n=-2$. The sinusoidal graphs above $E_\mathrm{abs}$ plots are representative of the electric field variation across microstrip line throughout the unit cell. (c) Unit cell with single large meander. Radiation sources for a single large meander are depicted in the figure. The four radiating magnetic current sources are shown at points $\mathrm{A}$, $\mathrm{A_1}$, $\mathrm{B}$ and $\mathrm{B_1}$. (d) Brillouin diagram for the unit cell with the single meander. (e) Unit cell design with two additional meanders that results in 12 radiation sources. (f) Brillouin diagram for the improved unit cell with two additional meanders.
• Figure 4: Normalized RHCP and LHCP gain in the H-plane obtained from simulation for the formed by connecting 10 unit cells with singular meander. The main lobe is due to spatial harmonic of $n=-2$. The realized gain of the main lobe varies from 8 to 14 across the frequency range.
• Figure 5: Axial ratio values in the main beam direction versus frequency obtained by full-wave simulation of 10 unit cells connected in series for 3 cases: (a) single meander with $\phi_{\mathrm{AA_1}} = \pi$, (b) single meander with $\phi_{\mathrm{AA_1}}=9\pi/8$ to reduce the period of the unit cell and in presence of two additional meanders on either side of large meander (with $\phi_{\mathrm{AA_1}} = \pi$) with the size (c) ($\phi_{\mathrm{sect}}= 10\degree$) and (d) ($\phi_{\mathrm{sect}}= 25\degree$).