Full-Wave Modal Dispersion Analysis and Broadside Optimization for a Class of Microstrip CRLH Leaky-Wave Antennas

Abstract

In this paper, a planar microstrip composite right/left-handed leaky-wave antenna is analyzed and designed as an infinite I-D periodic microstrip leaky-wave antenna. A parametric study, based on a full-wave numerical modal approach that analyzes a unit cell using a periodic layered-medium Green's function, is shown to be an efficient approach to accurately design the structure, completely eliminating open-stopband effects and achieving an almost constant radiation efficiency when the beam is scanned through broadside. Results obtained by the proposed approach are compared with those obtained by means of both an artificial transmission-line analysis and a Bloch-wave analysis, which use the fullwave simulation of a finite-length structure. The balanced condition is interpreted in terms of the behavior of the phase and attenuation constants relevant to the radiating harmonic. Furthermore, it is shown how radiation at broadside is guaranteed by the presence of two radiating elements (one series and one shunt) within the equivalent circuit of the unit cell. The effectiveness of the analysis is demonstrated through the design of a finite-length antenna excited by a source at one end

Dirac leaky-wave antennas for continuous beam scanning from photonic crystals

“…The figure also depicts how the leakage constant does not vary close to the G-point, contrary to typical LWAs. Various effects such as an open stopband or not supporting the appropriate radiation mechanisms typically manifest themselves with abrupt variations in the leakage constant around broadside in LWAs 21 .…”

“…It was demonstrated at microwaves that the stopband can be closed in transmission-line metamaterial LWAs, by 'balancing' the shunt and series transmission line impedances [19][20][21][22] . Such antennae can be simply identified as transmission lines with sub-wavelength unit cells having both series and shunt lossy resonators.…”

“…When the two resonant frequencies are made equal, a closed stopband situation arises. In addition, the existence of both series and shunt radiation resistances that have a specific ratio in the unit cell is a necessary condition to achieve actual broadside radiation even under the balanced condition 21 . Elimination of the open stopband in one-dimensional (1D) periodic printed LWAs at microwaves was demonstrated in ref.…”

“…These concepts have so far been demonstrated only at microwaves. Primarily this is because they are either applicable to periodic structures with a very subwavelength unit cell period (( l g ) such as transverse electromagnetic (TEM) and quasi-TEM mode (mainly microstrip type) LWAs, or require situations where it is possible to realize printed circuit or stub elements, or more complicated unit cells with additional mechanisms 22,23 , and/or situations where it is appropriate to apply transmission-line modelling as in refs [19][20][21][22] to determine the balanced condition and close the stopband.…”

“…21), to enable true unilateral broadside radiation and continuous beam scanning. Such structures are extremely useful for reliable leaky-wave operation, especially at higher frequencies beyond microwaves.…”