Patent Application
20230246344
This patent application relates to microwave devices, and more particularly to microwave waveguide transitions.
Waveguide transitions are radio frequency (RF) devices that provide RF transmission transition between different waveguides or antennae. Some examples of applications for which they are used are in RF/microwave systems, including Wi-Fi, radio, cellular, satellite and other communications, RF/microwave heating in food, chemistry and other industries, and chemical reaction enhancements for emissions aftertreatment, chemical synthesis and various external/internal combustion engines and jet engines.
Some of the major challenges in waveguide transition design are to provide a smooth transition between hollow and solid waveguides or antennae, to achieve high transmission efficiency and low reflection for a wide operating frequency range, and to transmit high power microwave energy.
A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:
The following invention is directed to a waveguide transition that launches a high-power microwave signal from an air-filled waveguide into a solid waveguide whose end face is a radiating aperture antenna. The transition provides a small-sized and high-performance device that smoothly transitions from different size waveguides or antennae for efficient, wide-band and high-power transmission.
The invention enables using reduced-size waveguides and antennae that can be installed for space-limited applications. The transition may be constructed from materials especially suited to withstand harsh working conditions (high pressure, high temperature, and high chemical reactivity). Examples of such applications are heating chambers, chemical synthesis chambers, aftertreatment reactors, combustion vessels, and internal combustion engine cylinders.
An example of microwave energy transmission for which transition 10 is designed is 8-12 GHz. This distinguishes transition 10 from other transitions, such as for coaxial cable, which are unsuitable for such transmission energy.
In the example of this description, waveguide 11 is a conventional rectangular waveguide. Specifically, waveguide 11 is a straight waveguide section designed for interconnections, having an attachment flange 11a. Such waveguide sections are commercially available in various sizes, lengths, and frequency ranges. Examples of typical straight waveguide section configurations are in size ranges from WR-10 to WR-137, lengths from 3 to 12 inches, and frequency ranges of 5.85 GHz to 11.0 GHz in thirteen waveguide bands. These specifications are examples only; the invention is not limited to use with waveguides with these specifications.
Waveguide 11 need not be a straight waveguide; waveguide sections are available with various bends and twists. Furthermore, waveguide 11 need not be rectangular and may be some other hollow (air-dielectric) waveguide, such as an elliptical or circular waveguide.
Waveguide 11 has a tuning screw 11b through its wall. This permits fine-tuning of the center frequency of operation. Transition 10 need not cover the full frequency bandwidth of waveguide 11, and tuning screw 11b provides a fine-tuning function to optimize the transition performance at a chosen frequency of operation. A target frequency band for antenna 12 may be selected.
Transition 10 comprises an attachment flange 10a, a support housing 11b, and a ceramic rod 10c. Attachment flange 10a is “compatible to” the attachment flange 11a of waveguide 11, meaning that it is shaped and sized to provide a tight connection to flange 11a and has a central waveguide opening. Flanges 10a and 11a may be provided with bolt holes and may be bolted together. When attached, flanges 10a and 11a provide a central air passage from waveguide 11 into chamber 11b.
Rod 10c is a solid piece of high-dielectric material. A suitable material for rod 10c is ceramic, specifically, a low loss microwave dielectric ceramic. However, some other homogenous high dielectric constant material could be used. In the example of
An upper portion of rod 10c, which extends through and above flanges 10a and 11a, provides the antenna for microwave transmission. The antenna is implemented with a radiating aperture at the end of rod 10c. In other words, only the end face of rod 10c radiates microwave energy.
Support housing 11b is a rigid structure that surrounds some or all of the upper portion of rod 10c. It provides support and protection for the upper portion of rod 10c. It may be made from a material designed to withstand harsh environments, such as a ceramic.
A lower portion of rod 10c extends into waveguide 11. The portion of rod 10c that extends into waveguide 11 functions as a matching transformer between the air-filled waveguide mode of waveguide 11 and the solid cylindrical waveguide mode of antenna 12.
The upper portion of rod 10c is metal plated. As a result, the metal plating contains a cylindrical waveguide mode within rod 10c within cylindrical boundaries. These plated portions of rod 10c result in rod 10c functioning as a cylindrical waveguide with a radiating aperture antenna. On the lower portion of rod 10c, which extends into waveguide 11 there is no such plating. The end faces of rod 10c are not plated.
Optionally, to prevent breakage or fracture of ceramic rod 10c, a sleeve 10d may be attached to chamber 10b, in which case, rod 10c is inserted through the sleeve. An appropriate material for such a sleeve is brass.
In operation, transition 10 transitions microwave energy from a standard (air-filled) waveguide to a much smaller (dielectric-filled) waveguide whose end face forms a radiating aperture (antenna). In the example of this description, the cross-sectional area rod 10c can be approximately one-third that of a conventional circular waveguide. With appropriate higher-dielectric ceramics, the size of rod 10c could be made even smaller. An advantage of ceramic materials is that their high strength, melting point, and heat conductivity make them durable as well as suitable for harsh environments.
The small size of transition 10 provides the ability to inject microwave energy into a small structure (such as an engine cylinder), which would not be possible with an air-filled waveguide.
In particular, when antenna 12 may be used to introduce a high-power microwave field into a combustion chamber containing an air-fuel mixture for the purpose of enhancing combustion. Because rod 10c functions as an antenna via only its radiating end face, it may be implemented as a small antenna port 12 within the combustion chamber 51. This radiating port 12 may be implemented by fitting the radiating end of rod 10c into an aperture in the chamber wall, such that the radiating end (antenna 12) is flush with the inner wall of the chamber. In other embodiments, it may be desired to have the rod 10d extend into a combustion chamber. A combustion chamber may be equipped with more than one radiating antenna 12.
