Ask Harlan: September 4, 2003
Harlan Howe is back with more answers for you!
YOUR RF & MICROWAVE TECH Q&A RESOURCE
You may know Harlan Howe from his twelve years as publisher and editor of Microwave Journal ®, or from his 34 years as a Microwave design engineer and engineering manager, or from his service as an IEEE fellow and past president of MTT-S.
Now, although semi-retired, Harlan is available to answer your questions about RF and Microwave engineering. If he doesn't have the answer, he will find an industry expert who does.
FROM: John Alderman, Alderhood Inc.
I need a source of microwave in solid state form at under a hundred watts -- perhaps below ten watts at 2.4 GHz. This is for a field portable chemical process so it needs to be small, light weight, efficent, and as inexpensive as possible. It does not have to be hi-fidelity or stable as it is being used to heat and excite a process. It would be especially good if could initiate then reduce power to a setting. Your help in this is appreciated.
I am not aware of any commercial product that fits your needs, however, it should be easy to make a source from a low cost oscillator and a power amplifier. If the amplifier does not have a gain control, the addition of a variable attenuator between the oscillator and amplifier should give you the control that you want. I suggest that you check the listings for manufacturers of these items in our buyer's guide on this web site. It can probably be assembled from standard parts.
First, thank you very much for answering questions.
I simulated a parallel coupled strip-line filter at center frequency 1.2 GHz and fractional bandwidth is 0.1 with HFSS software, but simulation results show 70 MHz shift downward in frequency response.
Which parameters of the filter effect the center frequency if permitivity and dielectirc thickness are constant?
I would be pleased if you help me.
The center frquency is controlled by the length of the resonators. The reason for the downward shift is due to capacitive fringing at the ends of the resonators, which makes them appear electrically longer than they are. If you shorten the resonators by the percentage amount of the shift, it should bring it on to the desired frequency.
FROM: Joe Zhou, COM DEV Ltd
I know a paper published by Microwave Journal some years ago. How can I find it ? Can I use the key words or subject or anything else to locate it?
We do not have a full keyword search for papers older than five years. [Ed note: limited articles are available from 1995 and 1996, primarily each month's cover story.] If you can provide us with the year, an author or a title, we can send you a photocopy of the paper. Send full contact information and the specifics of your request to firstname.lastname@example.org.
FROM: Cynthia Allen, I AM REALTY
I would like to know what type of device (remote also) can create a pulsed vibration? Where and how could it be connected?
How can the television be used as a video and audio transmitter?
The types of devices I am referring to can be felt by anyone in the given area?
Example: If I was sitting in a chair - I can feel a vibrating sensation.
Cynthia D. Allen
High power loudspeakers can transmit vibrations in the same way that you can feel vibrations from a loud drummer in a rock band. Except for this type of vibration, a TV set cannot transmit video or audio since it is only a receiver.
FROM: Mi Zhou, UESTC (China).
Dear Mr Harlan,
I'm a post-graduate major in microwave circuits and systems, and I'm confused about the future of Microwave circuits. With the development of MMIC,will the RF and Millimeterwave System-on-Chip be commercially available? or MCM technology predominate over the market? and will Hybrid MIC be knocked out? I want to know which field is most promising in future. Thank you.
The MMIC, RF and Millimeter Wave System-on-a Chip is available now for some applications. The MCM approach fills a need for complex systems using optimized individual chips. Hybrid MIC, while older technology, is still viable for many applications. I don't expect that any technology will be "knocked out". After all, people are still using waveguide for applications where it is best suited.
Of the three technical fields, MCM requires knowledge of both MMIC and packaging techniques and will probably give you the most flexibility.
FROM: Jesse Sheinwald, Telular
BNC stands for bayonet Neill Concilman. Neill and Concilman were connector designers at Amphenol. I used to deal with a sales manager at Amphenol who was a cousin of the Neill. Neill is also the N in N-connector.
The "bayonet Neill Concilman" definition of BNC is indeed correct and is one of about half a dozen established definitions. I chose the more generally used definition in my original answer. Thanks for the additional information for our readers.
FROM: Anil Agrawal, Qualcomm
Do you know of an equation that modifies the conductivity of a conductor based on its surface roughness? Also, if you could give the reference for that equation.
P.S.: In one of your previous responses to questions you mentioned that maybe someone could respond to that question. This column does not list email of the person asking the question. How can we respond then if we wanted to respond to other people's questions?
I am not aware of any simple equation that will give you the answer. The effect of surface roughness is related to skin depth, which is inversely proportional to the square root of frequency and conductivity. None of the books in my library even mention surface roughness, although we all know that "smoother is better." I'm sure that someone has done a thesis or research paper on the subject. Perhaps one of our readers may be able to provide a reference.
In answer to you second question, we are not providing e-mail addresses to protect privacy. If you want to respond to a reader, please send the information to me and we will forward it.
[Ed note: in the coming months, MWJournal.com will be expanding the Ask Harlan feature to include an interactive discussion board where you can continue discussing topics with your colleagues. Stay tuned.]
FROM: Jay Patel, Paratek Microwave, Inc.
My question concerns the RFID industry. I am trying to figure out which polarization would be the best choice if I were trying to design an antenna to meet many of the RFID tag makers requirements. I know most of the tags are designed to be linear (either horizontal or linear depending on how the package is placed). Some companies use circular polarization to avoid the package placement issue. Do you think it is better to design a 6 dB (FCC limit) linear pol antenna or a 9 dB circular pol antenna in hopes to provide a solution to satisfy multiple RFID manufacturers?
My own feeling is that the circularly polarized antenna will have a wider future market.
FROM: Hosain Menshady, IEI
Please spend a few valuable time for answering to my request.
I want to design a wideband VCO/Synthesizer with following important specifications:
3-Necessary tuning voltage for "VCO" is:1-12volt
If you have any suggestion for optimized design I will be happy.
I would appreciate if you help me in selecting the proper Synthesizer,prescaler, etc.
I am looking forward to hearing you.
Designing a wideband VCO/Synthesizer is a little beyond the scope of this column. I can suggest several good books on the subject that may be of some help to you.
Oscillator Design and Computer Simulation , Randall W. Rhea, Noble Publishing, 1995, ISBN # 1-884932-30-4
Nonlinear Microwave and RF Circuits , Stephen A. Mass, Artech House, 2003, ISBN # 1-58053-484-8
RF and Microwave Oscillator Design , Michal Odyniec, Artech House, 2002, ISBN # 1-58053-320-5
FROM: Gao Yuanci, UESTC
Does the millimeter wave really have efficient bio-effect?
Millimeter waves are part of the electromagnetic spectrum like radio waves and microwaves. They have a bio-effect only if the power levels are high. The safety standard for non-ionizing radiation is contained in the ANSI-C-95 standard , which is available from ANSI and IEEE.
FROM: Zhang Kai, UESTC
I don't how to calculate the impedance of the coplanar strip and coplanar waveguide with finite ground. Reading about the impedance for the coplanar strip, I found the paper-synthesis formulas for coplanar lines in hybrid and monolithic MICs, (Electronics Letters 1996 Vol.32 No 24). The formulas the author gave, I calculated with matlab, but they are wrong! Would you like to give me some advice!
This is not a simple problem, as you have already found out. There is a software package called EMPLAN: Electromagnetic Analysis of Printed Structures in Planarly Layered Media , Software and User's Manual, By Kinayman and Aksun, Artech House, 2000, Software No. U31849.
I think this may solve your problem.