An approximate analytical method based on experimental results for predicting the coupling characteristics of various coupling structures is described. Expressions for the propagation constants were derived using the generalized effective dielectric constant method. For nonsymmetric coupling structures, the theoretical coupling coefficients were modified by a correction factor. Comparisons between experimental and theoretical results are presented.

Coupling Characteristics of Planar Dielectric Waveguides of Rectangular Cross Section

Rectangular dielectric waveguide and its optimal transition to a metal waveguide

We present experimental results on a leaky wave antenna built from an inverted strip dielectric waveguide, in a frequency range going from 64 to 74 GHz. We study the frequency scanning for inclined backward beams, and the variations of gain and 3 dB beamwidth. We propose an approximate analysis for calculating the main lobe angle, and the radiating space harmonic's amplitude. Comparison between experimental and theoretical results makes appear that the angle's value (for inclined beams) is very sensitive to machining tolerances.

Leaky Wave Antenna Using an Inverted Strip Dielectric Waveguide

Multicolor capabilities, high detectivity, and quick response are highly important for advanced infrared sensor systems.
Photodiodes made of narrow-band semiconductors are widely used in such applications. However, the photodiodes
require cryogenic temperatures and are expensive. Less expensive uncooled bolometric detectors are less sensitive,
significantly slower, and have no multicolor capability. In order to overcome abovementioned obstacles, we have been
developing infrared detectors consisting of a dielectric rod antenna (DRA) in conjunction with a nanoscale metalinsulator-
metal (MIM) tunnel diode. In these assemblies, the DRA amplifies the incident electromagnetic radiation, and
the induced infrared frequency voltage is rectified by the MIM diode connected between the DRA and the ground
electrically conductive plate, thus transforming the electromagnetic energy into a useful electrical signal. Because of the
antenna's directional selectivity and using an MIM diode having the extremely low tunneling time and nanometer size
contact area, such a detector can respond at terahertz frequencies at room temperature. It has been shown that DRAs
made of high resistivity silicon posses low loss and enhanced gain at long infrared wavelengths. The proposed
approach demonstrates the inherent benefits of a nanoscale device manufacturing technique that is compatible with
existing CMOS technology, which may lead to the design of low cost sensors and/or sensor arrays for use in military
and commercial applications.

Uncooled nanoscale infrared high-speed sensors for missile seeker applications

The propagation and loss characteristics of the suspended H-waveguide, a new dielectric waveguide structure for millimeter-wave applications, are described. Both the mode-matching and the effective dielectric constant techniques are investigated. Some novel applications of the suspended H-waveguide are also presented.

Suspended H-Waveguide and its Millimeter Wave Applications

A novel dielectric waveguide that simulates optical graded index fibre is proposed for millimetre-wave applications. It is shown that a gradually varying refractive index across the guide can result in a well confined, single-mode propagation even in a guide several wavelengths wide. The desired index profile is achieved by varying the thickness or height of the waveguide. The effective-dielectric-parameter concept is introduced and used in generating the thickness profile which is approximated by a roof-top. Experimental results for a trial guide are presented and discussed together with the relative merits of this guide.

R. Menendez

Papers

Effective graded-index guides for millimetre-wave applications