(affordable) shielding options for some DIY microwave (up to 12GHz) projects ? - Page 1
Forum section: electronics / rf-microwave

author: prutser
author_rank: Regular Contributor
timestamp: July 28, 2023, 08:40:00 am
content: I am looking for some tips with respect to (affordable) shielding options for some DIY microwave (up to 12GHz) projects.Several options for small modules:- Standard aluminium die-cast enclosures (such as from Hammond)- Aluminium extrusion enclosures- Bare PCB, but soldered shielding cans on PCB- Milled RAW aluminium (using Schaeffer frontpanel service)Many (expensive) commercial modules use milled aluminium. Aluminium may oxidize, how is this WRT to shielding ?- Any other suggestions ?Also looking for a way to shield the individual sections of a filterbank on a PCB (up to 8GHz)Any suggestions, tips, examples ?What distance to keep between milled top and transmission lines which cross milled section boundaries ? Any rule of thumb ?Thanks in advance for any tips.I

author: rhb
author_rank: Super Contributor
timestamp: July 28, 2023, 01:34:57 pm
content: Consider buying or making a small bending brake and using galvanized 28 gauge steel used for HVAC ductwork. Most HVAC shops will give you a lifetime supply just for asking. WEAR LEATHER GLOVES!!! I had to get stitches for a cut for the first time in 70 years when a stack of scraps dislodged and grazed my finger tip on the way to the floor. Never felt a thing. Discovered it a minute or two later when I saw blood all over the place.Solders well so a strip of copper foil tape over the seam and soldered at a few tack points seems to work well. The steel attenuates the H field.If you figure out the dimensional part I'd really like to know that myself.Have Fun!Reg

author: mr ed
author_rank: Regular Contributor
timestamp: July 28, 2023, 11:11:23 pm
content: Brass shim stock is easily worked wi5h tin snips and soldered. Or, buy cheap small Chinese bias t modules and rip out the gurs. You get a milled box and 2 sma connectors fo 25 bucks - delivered.

author: David Hess
author_rank: Super Contributor
timestamp: July 28, 2023, 11:16:55 pm
content: For one-off projects, I like to make enclosures out of double sided copper clad board. Solder the seams on both sides to make the enclosure very strong as shown below.Quote from: prutser on July 28, 2023, 08:40:00 amA gasket which penetrates the oxidation is used, like sharp finger stock or wire braid.

author: rhb
author_rank: Super Contributor
timestamp: July 29, 2023, 04:53:51 am
content: FWIW Thin copper sheet is cheap ($0.05/sq inch for .1 mm $0.12/sq inch for .3 mm) and convenient for internal shields in DS PCB enclosures.SS FR4 with 1/8" wide (cut 1/4" in half) copper foil tape makes good 50 ohm microstrip. I use that and foil pads for my prototyping and experiments. Matching RF connectors e.g. SMA to the microstrip is difficult, but decent results are not two difficult. This is based on tests using a Tek 11801 & 20 GHz SD-24 TDR head.There should be examples in my thread on testing RF connectors and cables. If not I can add some tests on a 4" or so example.Reg

author: David Hess
author_rank: Super Contributor
timestamp: July 30, 2023, 02:33:05 am
content: Quote from: rhb on July 29, 2023, 04:53:51 amI have been thinking of making a small radial arm saw that uses Dremel cutting disks so that I can cut accurate strips of copper clad board for glue down microstrips.

author: rhb
author_rank: Super Contributor
timestamp: July 30, 2023, 03:26:45 am
content: Harbor Freight sells a small 4" table saw that I bought to make Manhattan pads. I then discovered foil on FR4 and now just use small squares of foil tape for pads. I doesn't have the aesthetics of a Chappy Happy build but it works very well.With a carbide blade it will do a good job, but you'll need to verify the impedance as it will change. I learned the foil tape microstrip from Thomas Lee's "Planar Microwave Engineering". To get consistent width a slitter is needed, but I haven't made one yet.I'll start up the 11801 and attach a couple of photos later.Have Fun!Reg

author: David Hess
author_rank: Super Contributor
timestamp: July 30, 2023, 02:39:18 pm
content: Quote from: rhb on July 30, 2023, 03:26:45 amHmm, Micro Mark has two even smaller table saws at 3-1/4 and 2 inch. The 2 inch carbide blade has a .043 inch kerf.I was thinking of a sliding table and fixed clamp to hold a Dremel using Dremel abrasive cut-off disks.

author: rhb
author_rank: Super Contributor
timestamp: July 31, 2023, 12:28:15 pm
content: The fence on the HF is pretty useless, but that's not hard to improve if you use it a lot. And for your application you would want a fence permanently hastened to the table to preclude changes in impedance.I need to make another 12" long microstrip test board as the first one has series parts inserted and the other pure line board is too short.Reg

author: David Hess
author_rank: Super Contributor
timestamp: July 31, 2023, 03:48:23 pm
content: Quote from: rhb on July 31, 2023, 12:28:15 pmI was going to make a screw driven adjustable fence and attach an inexpensive digital calipers to it.

author: rhb
author_rank: Super Contributor
timestamp: July 31, 2023, 08:28:15 pm
content: That would be useful if you changed substrates for higher frequency.