Coupling between different leaky-mode types in stub-loaded leaky waveguides

Abstract

Several leaky-wave antennas have been described in recent years that possess excellent properties, and they all have in common a parallel-plate stub guide of finite height as part of the cross section. For taller stubs and for larger leakage rates (wider radiated beams), some interesting new exotic interactions occur due to coupling between the desired leaky mode and another leaky mode, which is a modification of the “channel-guide” mode. Although we have described such coupling behavior briefly previously, this basic new feature (the coupling between two leaky (complex) modes) is not generally known, and is discussed here in more detail and in a more general context. In addition to a broad qualitative discussion, numerical results are presented for structures based on NRD guide and on stub-loaded rectangular guide. We believe that these effects are universal to all leaky-wave structures that possess a finite stub height in the cross section, so that the discussion here serves as a model for what to expect for other structures

Nonorthogonality Relations Between Complex Hybrid Modes: An Application for the Leaky-Wave Analysis of Laterally Shielded Top-Open Planar Transmission Lines

“…This type of leaky mode appears between the parallel plates and has been studied for a large variety of laterally shielded leaky-wave antennas [16]. Although the "channel-guide" modes are not desired, in practice, their propagation properties must be studied since they can couple with the wanted leaky mode, as can be seen in Fig.…”

“…Among these types of modes, we can find "channel-guide" leaky modes and evanescent modes below cutoff. It is very important to precisely study their propagation features since "channel-guide" leaky modes can couple to desired leaky modes [16], and modes below cutoff are essential to characterize discontinuities [2], [3].…”

Design of tapered leaky-wave antennas in hybrid waveguide-planar technology for millimeter waveband applications

“…The effect of the finite stub height ( , according to the schemes in Fig. 1) is critical, since it involves the appearance of channel-guide leaky-modes, which can couple to the desired leaky-wave mode, spoiling the antenna performance [15]. To the authors' knowledge, it is the first time that a full-wave method is applied to study the different possible tapering topologies for LWA in hybrid waveguide printed-circuit technology, taking into account all higher-order effects derived from the finite dimensions of the antenna, and without any restrictions on the geometry, neither for the printed-circuit perturbations (slot and strip width and position ) nor for the parallel-plate stub height, .…”

“…As a result, it is determined which taper topology is the best suited to modify the leakage constant of the leaky-mode while maintaining unchanged its phase constant, as previously explained. Section III makes a deep study in the effect of the stub length in the different tapering topologies, showing both the influence of coupling with unwanted leaky-modes (channel-modes [15] and slot-mode [16]) and the control of the polarization purity of the antenna. To obtain these parametric results, a full-wave two-dimensional technique developed in [10], [11] is used.…”

Dual polarization antenna fed by a dual mode substrate integrated NRD-guide

“…This arrangement produces a small asymmetry along the height of the NRDguide but is unsufficitent to generate significant leakage losses [6]. Simulation is done with a commercial finite integration time domain simulator [7], using a simplified NRD-guide model [5], Fig.…”