You may also wish to look out for an article entitled "How to design wide band RF quadrature networks" Page 5, QEX, November 1982, published by The American Radio Relay League.
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Another source is "The theory and design of lumped element quadrature hybrids"? which can be downloaded at
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There is also an excellent book devoted to the subject, which I think was written by the same person, and based on his Phd, but I can't find the details at the moment.
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Regards,
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Martin
