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A theory for the design of multiple-branch waveguide couplers is described which is based on field expansion into suitable eigenmodes and field matching at the discontinuities. Fringing fields and power transmission due to higher order mode excitation, mutual interaction between coupling branches, and frequency dependence of the coupling can directly be included in the computations by this theory. Together with the Fletcher-Powell optimization procedure the direct numerical synthesis of branch dimensions is possible which requires no additonal corrections. Design examples are given for Ku-band lOdB-, 8dB-, 6dB-, and 3dB-5-branch couplers. Measurements verify the theory.Übersicht: Eine Theorie zum Entwurf von Mehrfach-Abzweighohlleiterkopplern wird beschrieben, die auf der Reihenentwicklung der Felder in geeignete Eigenwellen und der Feldanpassung an den Stoßstellen beruht. Durch diese Theorie können Streufelder und die Leistungsübertragung aufgrund der Anregung höherer Wellentypen, die gegenseitige Beeinflussung der Koppel-Abzweigleitungen sowie die Frequenzabhängigkeit der Kopplung direkt in die Berechnungen mit einbezogen werden. Die direkte numerische Synthese der Abmessungen der Abzweigleitungen ist mit der Fletcher-Powell-Optimierungsmethode möglich, wobei keine zusätzlichen Korrekturmaßnahmen erforderlich sind. Entwurfsbeispiele für lOdB-, 8dB-, 6dB-und 3dB-5-Abzweighohlleiterkoppler werden für das Ku-Band angegeben. Messungen bestätigen die Theorie.Für die Dokumentation: Richtkoppler / Hohlleiterabzweigleitungen / Orthogonalentwicklung / Numerische Optimierung

Pseudobinary nitride alloys display enhanced piezoelectric properties compared to their nonalloyed counterparts enabling their wide application in high‐performance transducers and acoustic wave resonators. Their fabrication remains challenging because of their inherently stochastic nature, which requires in‐depth understanding of the film growth dynamics and the interplay of deposition parameters. Herein, thin Al1−xYxN films are produced with varied yttrium content in the range from x = 0.09 to 0.28 on a gradient seed layer on 200‐mm Si substrates and investigated via various X‐ray diffraction methods, high‐resolution scanning transmission electron microscopy, nanoindentation, and atomic force microscopy. Bulk acoustic wave resonators, solidly mounted on a multilayer acoustic isolation, are fabricated to analyze the piezoelectric performance of the films and to extract corresponding material parameters via fitting of the high‐frequency electrical response by 1D Mason's model. The trend of declining coupling is explained by the lattice softening and the increase in electron density, experimentally observed by monitoring reduced elastic modulus and dielectric constant values, respectively. The absence of expected enhancement of the piezoelectric modulus is interpreted by the presence of oxygen impurities, facilitating the inhomogeneous strain of the AlYN lattice, which effectively cancels the energy flattening phenomenon, found in III–V pseudobinary alloys.

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