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    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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"Short Length" Directional Couplers - RF Cafe Forums

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Post subject: "Short Length" Directional Couplers
Unread postPosted: Thu Jan 01, 2004 12:02 pm

Good day.

I have been told that the best physical length for a directional coupler is 1/4 wavelength. However, I have used many couplers that are much shorter then 1/4 wavelength.

I have been told that this is accomplished by balancing the even and odd mode impedances. Would it be possible for you to tell me were I can find information about this. I do not care if it is a website, magazine or book.

Thank you for your time and help.


Post subject: "Short Length" Directional Couplers
Unread postPosted: Fri Jan 02, 2004 3:53 pm

Welcome to forum!
There are many different techniques to bring about the physical realization of passive couplers (i.e. Cross-Band Couplers, Directional & Dual-Directional Couplers). In your case, Directional Couplers with less than quarter-wavelength (<1/4 WL) is possible and can be done dependent upon your applications. I have recently designed 4 ports Directional Couplers with < ¼ WL at Fc at 5.4521…GHz and other in 18.7145…GHz for low-power applications using Microstrip technology and with internal 50 Ohm/Z terminated and other with external 50 Ohm/Z connected to an RF Amplifier…) Sorry OEM sold to is confidential! I also have designed substantial amount of them at high power level for VHF (RF sample)… and GSM radio applications. Now, there are several tradeoffs in < ¼ WL Directional Couplers design, benefits, cost and disadvantages to be consider (i.e. bandwidths, isolation, reverse power, directivity & power level, physical size, dielectric substrate material, thermal issues…etc). Sometime, one can be surprised what some old books can bring to light! Now, following are many books, articles and software. I'm confident some of them will be of your benefits. ... ftware.htm

In addition, I'm currently designing a micro-small Directional Couplers Stacked Technology (DCST) and will include several ports and <1/4 WL. I will be releasing this technology on the web as soon as we finish the legal and protection matter (patent).

I thought this might help you at this time. Keep in touch and Good luck!

John Pereira

Posted  11/12/2012
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