A novel leaky-wave antenna based on an image nonradiative dielectric guide with two dielectric slabs is designed, fabricated and measured. By selecting appropriate values of permittivities and thicknesses for the two slabs, the gain bandwidth can be enhanced to four times wider than the ordinary single-layer nonradiative dielectric antenna. With appropriate thickness of the dielectric slab, the beamwidth can also be adjusted.

This paper introduces a new concept—space equalization into mutual coupling calibration of digital beamforming (DBF) array. Based on the concept, combined optimization method (COM) is developed to minimize element pattern errors in specified narrow angle and keep global errors being suboptimum. By constructing the cost function of COM properly, the complete equations are derived for the calculation of calibration matrix. Experimental results show that COM calibrates element errors efficiently in constrained narrow space and eliminates mutual coupling errors and channel gain and phase errors in a broad angle region.

Radiation region for open guiding structures is known to be further divided into antenna- and reactive-mode regions, and there is no clear cutoff point defined between the two regions. For a leaky-wave antenna, it is crucial that the antenna is designed to operate in the antenna-mode region so as to increase radiation efficiency, whereas in integrated circuits, the leakage should be suppressed to avoid unwanted coupling among circuits. Therefore, a reasonable definition of the two above-mentioned mode regions is necessary. In this paper, we propose a simple, but good alternative to define these two regions by means of a new version of complex effective dielectric constant, where the complex nature is due to leakage rather than dielectric or metal losses, as is customary. With the new approach, the reactive-mode region is found to be consistent with the conventional concept, and our results are similar to those in the literature. The present technique, however, helps in a better understanding of the results in a much easier way. Furthermore, we find for the first time that the attenuation constant in the deep reactive-mode region can be divided into two separate parts, one is due to the cutoff effect, while the other is caused by the leakage effect. Simple closed-form expressions are derived to determine the two kinds of effects. One can, therefore, gain some insight into the leakage effect in the reactive-mode region. A nonradiative-guide leaky-wave antenna is then investigated as a showcase and low radiation efficiency is observed in the reactive-mode region.

Characteristics of a transverse slot in the upper plate of a nonradiative dielectric guide operating in the dominant LSE00 mode have been analyzed. A fundamental radiation phenomenon due to the open property of the guiding structure is observed theoretically. It is found that the propagation direction of the leakage covers the whole angular spectrum in the plane parallel to the metallic plates. Explanation to its physical existence is given. A simple, but efficient method is developed to determine its angular power density. Numerical computation shows that the leakage is substantially high when the slot is near resonance.

A new leaky nonradiative dielectric guide with a double-layer dielectric slab is investigated in this paper by combining a multimode network theory with a mode-matching method. Numerical results show that proper selection of the permittivities can vary the leakage constant over a wide range. A leakage constant larger than 10% of free-space wavenumber can be obtained easily without entering the cutoff region. Leaky-wave antennas with shorter length and medium gain can thus be developed. In addition, the present leaky guide possesses the advantages of simple fabrication and physical stability. Extensive numerical results are provided to guide the antenna designs.

The frequency selective characteristics of lossy dielectric periodic structures with arbitrary grooved profiles and any incident angle are analysed using a method which combines multimode network theory with the rigorous mode matching method. Based on this, the effects of dielectric loss on the selective behaviour are systematically studied. Some guidelines for the accurate design of the dielectric frequency selective surface are given.

Guided-wave characteristics of a new hybrid or composite structure that consists of a non-radiative dielectric (NRD) waveguide surface mounted on the top of a relatively thin dielectric substrate are presented. This proposed structure is thus no longer a conventional NRD guide because its asymmetry may potentially generate unwanted leakage loss. Detailed numerical results show that one of the most interesting features is that it can still preserve a great deal of the desired properties of the conventional NRD guide under certain circumstances. This structure allows for a direct hybrid integration of a planar microstrip circuit with the NRD guide, thus providing an alternative design building block to a class of 3D multilayered millimetre-wave circuits. Experiments further verify the low-loss characteristics of the structure. In addition, effects of the width of ground plane are also discussed to show its low or non-radiating guided wave properties. A basic guideline in the design of a low-loss surface mounted NRD guide is provided.

Nonradiative dielectric guides and H-guides are widely used in millimeter-wave integrated circuits and antennas. To analyze the behavior of discontinuities, obstacles, and slots in such structures, an increasingly used mathematical formulation is the integral-equation approach, for which Green’s function is required. Here, an efficient programmable full-wave Green’s function, due to a magnetic-current element placed inside the dielectric layer, is derived in the spectral domain. In the derivation procedure, the field is divided into two parts: the incident and scattering fields. The contribution of the surface wave is included in the scattering part, while the singularity, when the field and source points are the same, is presented in the incident field part. By doing so, one can deal with the singularity caused by the source and surface-wave poles encountered in the integration separately and freely. The Green’s function is then used to analyze the radiation characteristics of a single transverse slot in upper plate of the H-guide. The results obtained are in good agreement with experimental data available in literature.

Leaky-wave characteristics of a class of nonradiative dielectric (NRD)-guides with various shapes of trapezoidal cross section are systematically studied for their potential applications in low-cost millimeter-wave antennas. A numerical technique is applied to model these irregular structures. The technique is formulated by effectively combining a multimode network theory with a mode-matching method. Our emphasis in this work is on the investigation of parametric effects in connection with the trapezoidal dimensions on leakage properties of the NRD-guide. Extensive results are presented to derive some useful guidelines for the design considerations of new types of NRD-guide leaky-wave antennas.

A new approach is proposed for dielectric multistep discontinuity in guiding structures which combines edge-element analysis with the mode-matching method and multimode network theory. It is demonstrated that the approach has the generality of the edge-element analysis and the simplicity of the multimode network method, while retaining the high accuracy of the mode-matching method. The calculations for different multistep discontinuities verify the effectiveness and suitability of the approach for analysis of three-dimensional (3-D) lossy dielectric discontinuity problem.