Hanyang University MODERN ANTENNA HANDBOOK by CONSTANTINE A

Hanyang University MODERN ANTENNA HANDBOOK by CONSTANTINE A. BALANIS ch. 3. 5. 4 – 3. 5. 8. 3 Kim Sung Peel 1/18 Antennas & RF Devices Lab.

Hanyang University Contents 3. 5. 4 Machining Operations 3. 5. 7 Special Conditions - 3. 5. 4. 1 Special Tools - 3. 5. 7. 1 Pressurization - 3. 5. 4. 2 Filleted Internal Corners - 3. 5. 7. 2 Passive Intermodulation - 3. 5. 4. 3 Swarf Control and Removal - 3. 5. 7. 3 Spaceflight Hardware - 3. 5. 4. 4 Chamfering and Deburring - 3. 5. 4. 5 Surface Finish 3. 5. 8 Examples - 3. 5. 4. 6 Component Handling - 3. 5. 8. 1 Machined Stepped or Corrugated Horns - 3. 5. 8. 2 Fabricated Horns 3. 5. 5 Welding, Brazing, and Soldering - 3. 5. 8. 3 Transitions 3. 5. 6 Bolted Joints 2/18

Hanyang University 3. 5. 4 Machining Operations • There is not much information about the important mechanical aspects of microwave structures available to a machinist not experienced. • A number of relatively simple but important aspects of microwave component fabrication that are sometimes overlooked between antenna and RF designers are worth discussing. - 3. 5. 4. 1 Special Tools • Many parts for aperture antennas can be machined using turning and milling tools with carbide inserts. • The machining of corrugated horns is an example. →Commercial carbide grooving inserts work extremely well, but these inserts do not always allow to fit into confined areas at the input end of a horn. →In these cases, special purpose tools can be made from steel bar and brazed-on carbide inserts, with cutting edges and angles. 3/18

Hanyang University 3. 5. 4 Machining Operations - 3. 5. 4. 1 Special Tools <Turning tools with carbide inserts> <Milling tools> https: //www. youtube. com/watch? v=9 r. Iwy. GOPb 0 o https: //www. youtube. com/watch? v=e 3 a. QYtm. ANRU <Carbide inserts> <Special purpose tools for corrugated horns> < Machining of corrugated horns > 4/18

Hanyang University 3. 5. 4 Machining Operations - 3. 5. 4. 2 Filleted Internal Corners • Fillet: rounded inside corner • The machining of a pocket or cavity on a milling machine naturally produces a cavity with rounded corners. • Deep cavities will take longer to machine if small milling cutter radius are specified. • Long milling cutters are prone to chatter when they enter filleted corners. • CNC(Computer Numerical Control) machines can reduce the tendency to chatter in internal corners. https: //www. youtube. com/watch? v=RNPoj. GFg 9 -8 < Chatter in internal corner> 5/18

Hanyang University 3. 5. 4 Machining Operations - 3. 5. 4. 3 Swarf Control and Removal • Swarf(Chips): debris or waste resulting from machining. • Swarf can be a significant cause of problems in the machining of antenna components. • The chips from aluminum and copper alloys are known as “long chip”, and these can become wrapped around cutting tools, damaging machined surfaces, occasionally causing tool breakage. • Many modern carbide tooling inserts are provided with “chip breaker” geometries to break long chips into short chips. • Corrugated horns are especially adept at trapping swarf in the corrugations. →Much care should be taken in the finishing of corrugated horns to detect and remove trapped swarf. <Long chip> 6/18

Hanyang University 3. 5. 4 Machining Operations - 3. 5. 4. 4 Chamfering and Duburring https: //www. youtube. com/watch? v=4 p. U_8 SO 7 f. MEhttps: //www. youtube. com/watch? v =4 p. U_8 SO 7 f. ME • Making all sharp edges to round edges for decreasing handling injuries. →This can be detrimental to the performance of some microwave devices. - 3. 5. 4. 5 Surface Finish • The finish on machined surfaces can be important to the functioning of an antenna component, especially at higher frequency. • A surface finish adequate to the task should be specified before manufacture. - 3. 5. 4. 6 Component Handling • Due to their relative softness, components made from aluminum and copper alloys require careful handling to avoid damage by scratching and denting. • Clean areas should be set aside for storage of components, and care should be taken with part handling both in and out of machine tools. 7/18

Hanyang University 3. 5. 5 Welding, Brazing, and Soldering • Some aperture antenna components require fabrication by welding, brazing, or soldering. • In choosing and applying a joining process, a number of issues should be considered. ①Suitability of process for the materials to be joined. →Aluminum alloys: easy to welding or brazing, but soldering is difficult. →Copper alloys: very easy to brazing soldering, but welding can cause porosity problems. ②Consider the heating effect of the process on the parts being joined. →Welding requires intense localized heating, which can lead to distortion of the parts being joined through thermal expansion stresses. →Brazing can be performed with either localized or generalized heating. Generalized heating can minimize thermal stresses during brazing, but can be difficult when parts are very large. ③Consider the strength required in the assembly. →Welding & Brazing joints: result in joints approaching the strength of the parent metal. →Soldered joints: much weaker than the parent metal. 8/18

Hanyang University 3. 5. 6 Bolted Joints • Any bolted connection in a microwave device must ensure adequate electrical contact at the internal edges to present an uninterrupted current path for the signal. • “Crush” flange joint: inside walls are contacted, while the remainder of the joint has a small definite gap(0. 1~0. 2 mm). →Drawback: Water can penetrating at open edge, possibly leading to corrosion. • “Contact” or “relieved” flange joint: two contact faces at inner and outer edges with the bolts in between. →Contact pressure is shared by both faces, so contact pressure at inner wall is reduced. →Outer contact provides improved protection from corrosion. < “Crush” flange joint> < “Contact” or “relieved” flange joint> 9/18

Hanyang University 3. 5. 7 Special Conditions - 3. 5. 7. 1 Pressurization • Antenna systems designed for use in outdoor environments are often lightly pressurized with some kind of gas(dehumidified air, dry nitrogen, etc. ) to ensure water cannot enter. • Sealing such systems to hold internal pressure requires radome covering the aperture and seals at each joint to prevent leakage of air or gas. • O-ring: specially molded silicone rubber seals to protect the system against weather and to retain air or nitrogen. →In designing the proportions of O-ring grooves for sealing, the grooves’ diameter should be larger than that of O-ring. < O-ring for sealing of pressurization> 10/18

Hanyang University 3. 5. 7 Special Conditions - 3. 5. 7. 2 Passive Intermodulation(PIM) • PIM is the generation of interfering signals caused by nonlinearities in the mechanical components of a wireless system, especially anywhere that two different metals come together. Junctions of dissimilar materials are a prime cause. →low PIM is an antenna system is as much a result of good hardware design and fabrication. • For reducing PIM, the number of parts and there for joints must be kept minimum, and the same material should be used throughout the assembly. - 3. 5. 7. 3 Spaceflight Hardware • The extreme environment of space imposes some stringent requirements on hardware design and fabrication. • Materials used in flight hardware subject to large temperature variations, solar radiation, extremely high vacuum, severe shock and vibration during launch. • Extremes of temperature can lead to problems between differing materials. →The effects of differential expansion must be assessed. • Must be assessed for effects of radiation and high vacuum. →Many materials degrade, loss mass under these conditions. 11/18

Hanyang University 3. 5. 8 Examples - 3. 5. 8. 1 Machined Stepped or Corrugated Horns →milling & turning 12/18

Hanyang University 3. 5. 8 Examples - 3. 5. 8. 1 Machined Stepped or Corrugated Horns • Boring bar on the left has a smoothly curved top face on the carbide to promote chip flow out of the corrugation, while the other has a chip breaker geometry. • Boring bar’s maximum possible size: it can clear both the front and rear walls during turning. • It will probably be found that any grooving boring bar will tend to chatter at the bottom of the corrugation. →This can be prevented by reducing the spindle speed at the end of each cut. < maximum possible size of boring bar> 13/18

Hanyang University 3. 5. 8 Examples - 3. 5. 8. 2 Fabricated Horns • Rectangular horns, especially for large sizes, are often fabricated from flat sheet sections, joined by welding, brazing, or soldering, depending on the strength and accuracy required. • The typical joint configurations for these alternate joining methods are quite different. ①Corner joint of a welded fabrication: →Two flat sheets do not overlap: to ensure complete penetration of the weld pool toward the inner surfaces during welding to minimize gaps along the inside of the joint. →Backup bars may be placed on the inside of the joint to prevent burn-through of the weld pool and can be used to support the parts in correct alignment during welding and help minimize distortion. < Rectangular horn> 14/18

Hanyang University 3. 5. 8 Examples - 3. 5. 8. 2 Fabricated Horns ②Corner joint of a brazed fabrication: →One of the sections to overlap the other: overlapping section is extended past the outside surface of the joint to create a lip to which filler metal can be applied by hand. →Filler metal flows through the joint to form a small fillet on both sides. 15/18

Hanyang University 3. 5. 8 Examples - 3. 5. 8. 2 Fabricated Horns ③Corner joint of a soldered fabrication: →Low strength of the filler metal usually requires additional reinforcement of the joint in the form of cover strips. →Use of a reinforcement along the outside of the joint to increase the surface of the solder joint. 16/18

Hanyang University 3. 5. 8 Examples - 3. 5. 8. 3 Transitions • Waveguide transitions are often needed to connect waveguides to the inputs of aperture antennas. • Where the transition provides a change in diameter of a circular waveguide, a turned component can be used. • Occasionally, a transition must also provide a change in waveguide shape. • A method that is often used to make such devices is wire electric discharge machining. (wire EDM) →Electrical discharge between a tightly stretched wire and workpiece is used to burn a slot in the workpiece, and so to saw out a hole or shape. https: //www. youtube. com/watch? v=p. Bue. Wfzb 7 P 0 17/18

Hanyang University Thank you for your attention 18/18