What is in this article?:
- Design Tips on Dielectric Waveguide
- Plating and preparing the raw substrate
- Attenuation of plated-dielectric waveguide & joining waveguide and fitting flanges
- Rf heating effect and the effect of solar heat
- Heat transfer and temperature stability
- Lightweight waveguide components, antennas, and feed systems
Lightweight waveguide components, antennas, and feed systems
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Lightweight waveguide components
Waveguide components developed using dielectric as a substrate are shown in Fig. 8.
The rectangular waveguide components were produced by grinding of the substrate which was Polystyrene 4 lb (comm.). The circular waveguide components, of the same dielectric substrate, were produced by turning. The copper plating of the substrates was performed by using either Shipley or Dynchem process.
The measured responses of several of the components are shown in Fig. 9. This method of fabrication allows a weight reduction of better than six to one over aluminum counterparts.
Lightweight antenna and feed system
A dielectric parabolic antenna and feed system is shown in Fig. 10. The antenna consists of a mirror. The antenna consists of a parabolic mirror; 18-in. in diameter with an f/d of 0.33.
The paraboloid was contoured from two solid sections of a low-loss dielectric substrate with a dielectric constant of 1.04 and loss tangent of 0.0004. Both sections of the substrate were pinned together with dielectric Dowell pins.
Due to the mirror’s size, copper plating was not possible, so the reflecting surface of the mirror was deposited by spraying with a fine silver-base lacquer, “Eccoshield ES.” The antenna feed is a dielectric conical horn integral with the parabolic mirror and fed with a circular dielectric copper-plated waveguide.
Lightweight components and integrated microwave subsystems, whose electrical performance is compatible with their conventional counterparts, can be easily and economically produced. Examples of such components are shown in Fig. 11. A complete TR subsystem, suitable for airborne operation, is shown in Fig. 12.
This new technique allows for rapid “bread-boarding” of complete subsystems. The only requirement is an inventory of straight waveguide sections plus E- and H-plane bends. With these components, the engineer can fabricate, without model shop assistance, any microwave component or subsystem and thus check a design in a relatively short time.
Recent studies point toward development of lightweight dielectric waveguide capable of carrying higher powers than are feasible to date. Such a waveguide is shown in Fig. 13. This new structure is of hexagonal cross section with rounded corners divided along its narrow dimension. Such a division is permissible because no current lines are broken by the division.
The waveguide would be constructed by casting a lightweight dielectric substrate with a density of 3.7 lb/ft3 and then copper plating. Both halves of the waveguide would be joined by dielectric Dowell pins and cemented with epoxy resin.
The purpose of the modified cross-section shape is to ease manufacture (small draw angle of about 2.5° allows for ease in withdrawing the mandrel). Rounded corners of about 0.03 in. facilitate mandrel withdrawal and allows for better adherence of copper to the dielectric substrate during plating. Mechanical inspection is also eliminated in that it is only necessary to inspect the original mandrel.
With this type of manufacture, which produces a different cross-sectional shape of waveguide, new waveguide dimensions are required as listed alongside the sketch.
This modified waveguide possesses the same guide wavelength as the conventional waveguide. Measurements of this parameter were conducted at X band, and the change in guide wavelength was 0.295%. The modified waveguide can be joined to conventional waveguide with good match. Also, the matching is independent of frequency. A prototype of the proposed modified waveguide at L band can be pressurized to 24.5 lb/in2.