Compact 3‐dB waveguide hybrid with full bandwidth

Abstract

A compact waveguide 3-dB hybrid with full bandwidth is proposed in this Letter. The tight coupling and full bandwidth of Ka-band (from 26.3 to 40 GHz) are achieved by introducing multi-sections of waveguide with different width and depth, together with loaded posts on the bottom of some waveguide sections. The whole structure is symmetric both longitudinally and transversely (patent pending). The measured results show that return loss and isolation of the hybrid better than 25 dB and 26 dB, respectively, phase difference of the two output terminals within 90°± 3°and the power-split unbalance within 3.1 dB ± 0.5 dB are achieved over the full Ka-band waveguide bandwidth. Introduction: The 3 dB waveguide hybrids are widely used in many microwave and millimetre systems for branching and synthesis of signal power as well as generating desired power splitting with certain specification requirements, such as power ratio, frequency bandwidth, directivity and so on. Ka-band is typically used for satellite communications for its significantly wide frequency bandwidth. Hence the design of a broadband waveguide hybrid has profound practical significance. To achieve wider bandwidth, many approaches have been proposed and practiced, such as using continuous apertures [1] configurations, narrow-wall structures [2] and multi-aperture [3-7]. These couplers mainly contain two inline waveguides, which are coupled through one of the narrow or broad walls. Several wavelengths long have to be taken to achieve 3 dB coupling and full bandwidth. Cruciform directional couplers in E-plane rectangular waveguide [8] or in H-plane rectangular waveguide [9], cavity-type directional couplers [10] and narrow-wall directional couplers [2] are compact and with tight coupling, however, their fractional bandwidth is less than 30%. This Letter will show the realisation of a compact Ka-band waveguide 3-dB hybrid with full bandwidth. The measured results indicate that from 26.3 to 40 GHz (entire Ka-band range), the coupling coefficient is 3.1 ± 0.5 dB, return loss and isolation of the hybrid are better than 25 dB and 26 dB, respectively; phase difference of the two output terminals is within 91°± 3°.

X‐band compact coaxial power combiner for high‐power applications

“…However, the cross-section size is larger than 1.75 λ, which is not suitable for compact applications. Wu et al proposed a compact broadband waveguide hybrid by introducing multiple transforming sections in [12]. Around 25-dB return loss, 26-dB isolation, and 3.1 ± 0.5 dB transmission coefficients are reached over a bandwidth of 41%.…”