At 08:02 03/08/2000 -0800, Ed Price wrote: >For emission testing, you might be able to get around high AF's by using a >high-gain, very low-noise pre-amp. See Miteq Corp for pre-amps. > Zhong made a very good point in that high gain goes hand-in-hand with high directivity, i.e. a radiation pattern which exhibits a narrow beamwidth. A narrow main beam is useless for most immunity testing, where the goal is to illuminate a substantial part of the EUT. It is also undesirable for emissions testing when the object is to measure narrow-beamwidth high frequency emissions originating from the EUT. Hence obtaining a horn with the highest possible gain is not necessarily the best solution.
>I think the best route to go is to build your own horns as needed. > >OTOH, I am currently waiting for delivery of two custom-built horns, with >low AF's, for the 18-26 GHz band and the 26-40 GHz band. For custom-built >horns, I suggest you contact: > <snip> It is pretty easy to design and build your own horn antennas, especially standard gain horns, if you have access to a metal shop. Most antenna labs I have worked with have a few homebrews in their antenna collection, some are of professional quality, some are quick-and-dirty solutions. I've even seen university labs perform measurements with antennas built out of a styrofoam coffee cup lined with aluminum foil (how's that for recycling!) and similar ultra low-cost solutions, with surprisingly good results. For standard gain horns and their cousins, design formulas can be found in antenna text books, and you can develop your own design compromise optimized for your measurement setup and tests requirements. In our lab most of the better performing antennas (horns, multibands, wire, microstrip, fractal) used in specialty testing apps are designed and built in-house. There are two areas where homebrewing gets challenging: a. coax-to-horn transition, aka antenna feed. For standard gain horns and like antennas, an off-the-shelf coax-to-waveguide transition for the correct frequency range will perform well. Simply solder the horn onto a matching flange, and you're in business. However, the antenna feed portion in multi-band antennas and other exotic designs can be considerably more troublesome. b. the performance verification/antenna calibration. You'll need a reference antenna with known performance for this, or a set of similar antennas, and fairly accurate instrumentation, or you'll have to send out your antenna to a qualified antenna cal lab capable of doing microwave frequency calibrations accurately. Simply building an antenna according to the design drawings does not necessarily mean it will perform according to the design specifications, unfortunately. It's even possible to build more exotic broadband antennas like ridged waveguide horns or flared horns in-house, but the design process is not as easy and straightforward (computer design effort required, typically) and the level of talent required to design and build those increases exponentially. As in: unless you have previous antenna design and manufacturing experience, don't bother trying, it's cheaper to simply purchase an existing design or have one designed and built for you. Or, sometimes it's possible to play with an existing antenna and tweak it to the performance you require. -Robert Robert Bonsen Principal Consultant Orion Scientific email: [email protected] URL: http://www.orionscientific.com phone: (512) 347 7393; FAX: (512) 328 9240 ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
