Multimode Rectangular Waveguide Research Articles

Free-Space Subterahertz-Field Polarization Controlled by Selection of Waveguide Modes

We study experimentally the free-space electro-magnetic field emitted from a multimode rectangular waveguide equipped with a diagonal-horn antenna. Using the frequency range of 215-580 GHz, a photo-mixer is used to launch a free-space circularly-polarized electro-magnetic field, exciting multiple modes at the input of the rectangular waveguide via an input diagonal-horn antenna. A second photo-mixer is used, together with a silicon mirror Fresnel scatterer, to act as a polarization-sensitive coherent detector to characterize the emitted field. We find that the radiated field, excited by the fundamental waveguide mode, is characterized by a linear polarization. In addition, we find that the polarization of the radiated field rotates by 45 degree if selectively exciting higher-order modes in the waveguide. Despite the higher-order modes, the radiated field appears to maintain a predominant Gaussian beam character, since an unidirectional coupling to a detector was possible, whereas the unidirectionality is independent of the frequency. We discuss a possible application of this finding.

A filter of H 0n modes in a multimode rectangular waveguide

A technique is developed for calculating the electrodynamic characteristics of a filter of H 0n modes in the case of various configurations of the filter and various combinations of its mechanical and electric parameters. In numerical computations, the complete set of the filter parameters is taken into account. It is shown that the number of absorbing elements in the filter can be reduced from three to two and that, simultaneously, the quality characteristics of the filter can be improved.

Transition, radiation and propagation loss in polymer multimode waveguide bends

Design curves for insertion loss of multimode polymer waveguide 90 masculine bends are reported as a function of bend radius for several waveguide widths. For the first time, to our knowledge, in multimode rectangular waveguides the insertion loss is resolved into its components of transition, radiation and propagation loss, in order of decreasing strength, separating them from input and output coupling loss by calibration and comparison of experimentally measured and beam propagation method (BPM) modeled curves. We used the method of nested bends for the first time in multimode polymer waveguides to calculate the propagation loss on a small substrate without using destructive cut-back. The lowest loss of 0.74 dB occurred for a 50 mum square cross section, Deltan=0.0296, 13.5 mm radius waveguide bend.

Micron-Sized Imaging System Based on Multimode Waveguides

The design and analysis of an extremely compact micron-sized imaging system consisting of a multimode rectangular waveguide is presented, and both the on- and off-axis imaging characteristics in the far field are studied. The imaging capabilities of this system are comparable to that of a high numerical aperture lens system with the advantage that it is extremely compact, simple to be fabricated and can be extended to arrays.

Wavebeam Multiplication Phenomena to RF Power Distribution Systems of High-Energy Linear Accelerators

A new quasi-optical concept of electrically proof Delay Line Distribution System (DLDS) for high-energy electron/positron accelerators is proposed. In order to increase microwave power, used for particle acceleration, the concept assumes summing up of a few wavebeams in multimode rectangular waveguide. Operating by mutual phases of the wavebeams, to be produced by coherent sources, the system allows also a distribution of long multiplied RF pulses on a set of acceleration sections. Calculations of key components are fulfilled at 34 GHz frequency.

Transformation of the near radiation field of semiconductor lasers by a multimode rectangular waveguide

A report is given of theoretical calculations and of an experimental demonstration of transformation of twodimensional amplitude-phase distributions of a radiation field generated by a single semiconductor injection laser or an array of such lasers. This transformation is performed by a rectangular waveguide with transverse dimensions which are large compared with the radiation wavelength. Consideration is given to ways of constructing two-dimensional light-emitting arrays of semiconductor lasers (both oscillators and amplifiers) with a coherent interaction of the fields.

Loss Increases in Multimode Rectangular Infrared Waveguides Due to Helical Deformations

The coupling coefficients for all TE/sub pq/ and TM/sub pq/ modes of multimode rectangular waveguides, caused by elementary rotations about the three axes of symmetry, are calculated in the microwave approximation. The modes b coupled to a common mode a by these independent rotations form three nonoverlapping families. Furthermore if a deformation consisting of no more than two of these rotations is considered, none of the modes b are coupled to each other by that deformation. These properties lead, in the case of mild deformations, to the formulation of a multimode coupling theory which shows that the loss increase due to such deformations can then be viewed as the result of multiple two-mode coupling. Explicit formulas are derived for the loss increase of TE/sub p0/ due to mild circular bending. Qualitative features of twists and helical deformations are also brought out.

A generalized approach to the analysis of infinite planar array antennas

In this paper a generalized expression for the complex power radiated by an element in an infinite planar array antenna is derived. Since this power formula applies to a large class of phased array antennas where the aperture field distribution can be completely specified (in normal mode form), it proves to be a powerful, unifying principle. The utility of this approach is illustrated by the simplicity with which previously known results can be derived; e.g., an infinite array of slots in a ground plane and an infinite array of flat dipoles with or without a ground plane. Further demonstrations of the usefulness of the power formula are provided by the systematic and straightforward solutions of the less-well-known problems of infinite arrays of crossed-dipole pairs and infinite arrays of open-ended rectangular waveguides. The waveguide array solution is particularly interesting because it reduces to a set of equations which are identical to those one would use to characterize an N-port network on an admittance basis (N is the number of waveguide modes). Since the power formula is derived for a parallelogram element Lattice, the resultant solution for a specific type of element is in its most general form. Expressions for the scan-dependent, dominant mode radiation admittance and the element gain function for a multimode rectangular waveguide radiator are also derived. In addition, various aspects of the waveguide array solution are investigated in the light of previous studies of infinite arrays.