Published in IET Microwaves, Antennas & Propagation Received on 17th May 2012 Revised on 28th September 2012 doi: 10.1049/iet-map.2012.0272 ISSN 1751-8725 Dual-layered substrate-integrated waveguide six-port with wideband double-stub phase shifter O. Kramer T. Djerafi K. Wu De´ partement de Ge´ nie E ´ lectrique, Poly-Grames Research Center, E ´ cole Polytechnique de Montre´ al, Montre´ al, QC, Canada H3T 1J4 Abstract: A dual-layered six-port front-end circuit on the basis of substrate-integrated waveguide (SIW) technology is presented and demonstrated. The use of SIW technology allows the development of a compact circuit with low radiation loss at millimetre- wave frequencies. The six-port architecture makes use of multilayer couplers that provide a wide coupling area through two slots; a new broadband SIW phase shifter composed of two H-plane stub lines and a reference line; and two SIW power dividers. The six-port design is free from loads as in the case of classic modified six-port architectures with eight ports. To validate the proposed concept, an integrated broadband six-port front-end circuit prototype was designed, fabricated and measured. Simulation and measurement results show that the proposed six-port circuit can easily operate at 60 GHz for V-band system applications. The two-layered structure presents interesting technological features including low profile, small volume and footprint and high- density integration. 1 Introduction Millimetre-wave access systems at 60 GHz are designed to support short-range point-to-point or point-to-multipoint data links in connection with broadband multimedia services [1]. These services include, for example, e- commerce, interactive video transmissions, or remote learning and telemedicine [2]. As an alternative to the classic super-heterodyne and homodyne techniques, six-port radio architecture was proposed for the development of low-cost and high-efficient direct-conversion software-defined transceivers, which are now becoming an attractive solution compared with the conventional mixer-based schemes because of its low- power consumption, good linearity and low system noise as well as low design and manufacturing cost [3, 4]. The six- port junction circuit is a passive interferometer device that essentially consists of several couplers, power dividers and one wideband phase shifter, and it can be considered as a black box with two inputs and four outputs. The output ports are terminated with power detectors. Characteristic relationship or correlation between the two input signals (phase and amplitude) can be determined by reading the baseband power information from the output ports. Substrate-integrated waveguide (SIW) technology has been found suitable for the design of six-port radio and radar [5–7] systems with the demand for low loss and low cost, as well as integration of high-density microwave and millimetre-wave components and subsystems [6]. To ensure wide-band performances of the six-port on the basis of SIW technology, both coupler and phase shifter must have wideband properties. In this work, a V-band six-port is proposed, which is based on the combination of two couplers and two power dividers with a broadband 908 phase shifter using H-plane stubs. The architecture leads to a six-port structure, which is different from the conventional types of six-port that generally have seven- or eight ports. In this case, excessive ports should be terminated by appropriate loads. The two-layer coupling structure is a very attractive scheme for the realisation of high-performance couplers using a wide coupling aperture, and also an SIW stub-based H-plane phase shifter is used to achieve the desired phase distribution. In this work, different components are first designed as fundamental building blocks of the six port. Parameters of these components are fine-tuned using Ansoft’s high- frequency structure simulator package to realise broadband performances. The broadband H-plane phase shifter is modelled, designed, optimised and measured. Combining the designed coupler and phase shifter, the six-port front- end circuit is then developed and optimised. To demonstrate the performances of the proposed six-port circuit, an experimental prototype is fabricated and measured. Simulation and measured results are presented and discussed. 2 Design framework The block diagram of the proposed six-port circuit is shown in Fig. 1. The six-port junction was designed with Rogers RT/ Duroid 6002 substrate with dielectric relative permittivity of 2.94 and substrate thickness of 0.254 mm (10 mil). As shown in Fig. 1, the six-port circuit is composed of two hybrid couplers, two power dividers and one two-stub phase shifter. The next sub-sections will describe in detail these different components. 1704 IET Microw. Antennas Propag., 2012, Vol. 6, Iss. 15, pp. 1704–1709 & The Institution of Engineering and Technology 2012 doi: 10.1049/iet-map.2012.0272 www.ietdl.org