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.

Click here to submit your question now.

FROM: Anil Agrawal, AT&T Bell Labs

Hi Harlan,
First, thanks for being available for answering questions...
I am looking for a paper, a book, or any source that describes design steps to design a Hairpin Bandpass filter in microstrip. I have researched few papers, articles, & a couple of books but none of them describe (at least not clearly enough) how exactly to design one. I am NOT looking for a filter synthesis program like Eagleware's M/Filter. In fact, I have access to it. But, even after using a filter synthesis program the EM simulation is way OFF. So, I would like to learn what parameters (and why) I should be "tuning" to get to the desired results. BTW, frequency in my application is 12 GHz or more.
Thanks again.



Dear Anil,

The design of a hairpin filter is not that different than the design of a side coupled filter except that the half wave resonators are folded. The original paper for this type of filter is "Parallel-Coupled Transmission-line Resonator Filters ", S.B. Cohn, MTT-6 No. 2, April 1958, pp 223-231. A procedure for calculating the even and odd mode impedances is also available in Chapter 7 of "Stripline Circuit Design ".

Once you have Zoe and Zoo, you will need to use one of the many design programs to translate them into dimensions for your particular construction.

Tuning is not recommended, since it requires loading the ends of the resonators, which is subject to variation with temperature. I suggest that you build the filter, measure it and adjust the artwork to bring it on frequecy.


Dear Sir

I`m designing a microstrip coupled line filter at 30 GHz. I have to place this filter in an enclosure. What are the possible consequences of doing so at mmWave frequency? What is the criteria adopted for choosing a suitable top cover hight? How can I predict the cavity resonance?

With best regards,



Dear Sanjeev,

The rule of thumb that I have used is to keep the cover height at least 4 times the substrate thickness. There may still be some effect since you are designing with coupled lines, which tend to increase the field above the substrate.

The resonant frequency of the package is difficult to predict since the enclosure is partially loaded with dielectric from the substrate. I suggest that you include some lossy material in the enclosure to damp out any resonance's.

FROM: John Ball, Northrop Grumman

How do I locate companies that manufacture DRFM?


Dear John,

This is a little outside my area of expertise, however, Michael Puttre, editor of JED, the Journal of Electronic Defense (, has four suggestions. They are:

Kor Electronics (

Avitronics (

EWST Ltd. (

EADS Airborne Systems (

Hope this helps.

FROM: Gal Teofil Ovidiu, University of Oradea

What are the names of free microwave ciruit design softwares and where kind I find them online?


I am not aware of any free microwave design software from commercial companies that make their living selling this material; they do not put it in the public domain. There may be some free software available from universities, however, it will probably be focussed on support of a thesis or a specific project and will not be general purpose software.

FROM: William Harlow, HEICO Corp.

Hello. My name is Bill Harlow I do acquisitions and work for HEICO Corp ( We are in due diligence on a microwave component manufacturer for the satillite industry. We could use a consultant who is very knowledgable to give us market,technology and competitive assessments. Can you get me in contact with someone? Bill (tel:305-374-1745).


The purpose of this column it to address technical questions of general interest to our subscribers. We are not in a position to recommend consultants, however, by posting your question some reader may contact you directly to offer services.

FROM: Gideon Argaman, Celletra

Where can I find your Book : "Stripline Circuits "? I have lost my copy several years ago and yet could not find another.


"Stripline Circuit Design " is still available from Artech House, 685 Canton St., Norwood, MA 02062 as part of their IPF® (in print forever) program. It can also be ordered from

FROM: S.D., Houston

Is there a Cliff's Notes version of Stripline Circuit Design ?



See answer above.

FROM: Joe Tauritz, University of Twente

Hi Harlan,

How do you submit new Event info? I have sent an announcement to "Contact us" but aI am not sure if that is the best procedure.

Best regards,

Joe Tauritz


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