This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS 1 Broadband Millimeter-Wave Beamforming Components Augmented With AMC Packaging Nadeem Ashraf , Student Member, IEEE, Ahmed A. Kishk , Fellow, IEEE , and Abdelrazik Sebak, Fellow, IEEE Abstract—For future millimeter-wave beamforming applica- tions, the improved designs of crossover and 90° hybrid coupler are prototyped. The wideband response of 30% is achieved at the center frequency of 30 GHz. The planar-single-layered structures are developed by using microstrip line technology, which is further augmented with the separate layer of artificial magnetic conductor packaging. The aim is to minimize the spurious radiation caused by the bends and discontinuities in the beamforming networks. For simulation purpose, CST Microwave Studio is used, and designs are fabricated and measured. For the first prototype, the measured crossover insertion loss is about 0.5 dB with ±0.15 dB variation within the operating region. The isolated ports show a maximum level of -15 dB. For the second prototype of hybrid coupler, -3.7 dB is measured at transmitted ( S 21 ) and coupled ports ( S 31 ) with the variation of ±0.25 dB as a magnitude imbalance between the output lines. The couplers’ isolation ( S 41 ) level is less than -15 dB. The through/coupled port phase difference ( 6 S 31 - 6 S 21 ) is 90° with ±3° variation in extreme cases within the frequency band of operation. Index Terms—30 GHz, 90° hybrid coupler, crossover, elec- tromagnetic bandgap (EBG), fifth generation (5G) prototyping, millimeter wave (mmWave), perfect magnetic conductor (PMC) packaging, printed ridge gap waveguide (PRGW), wideband beamforming. I. I NTRODUCTION B EAMFORMING is one of the key enabling technologies to realize future fifth generation (5G) of wireless commu- nication. Multibeam antenna system deployment is essential for this purpose. On a small scale, the sole implementation of digital beamforming can be realized by taking the RF signal directly from each antenna into processing units. However, for 5G large-scale antenna systems, this approach will not be energy efficient. It may result into substantial thermal losses in the electronics. To achieve energy/spectral efficiency in such systems, efficient analog beamforming networks are vital [1]. The main components in beam-switched networks are phase shifters and crossovers. Such designs are commonly realized by multilayer planar technology where the RF signals are coupled between the lines through a nonresonating aper- ture or proximity coupling of resonating patches [2]. Substrate- integrated waveguide (SIW) technology has the advantage of designing these components on the single substrate layer. For instance, the SIW technique is used to design a 4 × 4 Butler matrix for 60-GHz applications [3]. However, large- scale SIW implementation may exhibit high losses. Other Manuscript received June 4, 2018; accepted August 6, 2018. (Corresponding author: Nadeem Ashraf.) The authors are with the Electrical and Computer Engineering Department, Concordia University, Montreal, QC H3G 2W1, Canada (e-mail: n_ashr@ encs.concordia.ca; kishk@encs.concordia.ca; abdo@ece.concordia.ca). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LMWC.2018.2864883 Fig. 1. Microstrip circuit. (a) Three different kinds of waves in quasi-TEM structures. (b) Cross-sectional view and filed distribution [5]. modern circuit technologies, e.g., low temperature co-fired ceramic, are complicated and expensive comparatively. In the advancement of technology, the options are to utilize the existing low-profile legacy circuit technologies or to go for the new ones. In this regard, a microstrip line (MSL) technology has sev- eral advantages. The fundamental theory of RF and microwave coupled-line circuits is well established [4]. However, radiation losses are very critical at millimeter-wave (mmWave) frequen- cies. The radiation mechanism is linked to the excitation of three kinds of waves in quasi-TEM electromagnetic structures: radiated, leaky, and surface waves, as presented in Fig. 1 [5]. Therefore, spurious radiation/coupling must be minimized to utilize this technology for mmWave circuitry. In [6], perfect magnetic conductor (PMC) packaging was introduced and highlighted in [7] with the PMC packaging in mind. Further study at mmWave frequencies is presented in [8]–[10] and applied in filter design in [11]. The PMC is artificially realized by the 2-D distribution of electromagnetic bandgap (EBG) unit cells. This artificial magnetic conductor (AMC) is used to sup- press the packaging cavity modes. Likewise, the performance of the conventional MSL microwave components, as reported in [12], can further be improved by AMC packaging at mmWave. In this letter, packaged wideband mmWave crossover and 90° hybrid coupler prototypes are presented. The following objectives were under consideration: 1) single-layer substrate technology; 2) wideband response; and 3) minimizing radia- tion losses. As these components are the building blocks in the large-scale analog beamforming circuitry; therefore, AMC packaging may result into overall system-level performance enhancement. II. DESIGN DETAIL The 3-D exploded model view and design details are shown in Fig. 2. Layer 1 consists of 2-D distributions of EBG mushroom-like unit cells. The substrate RO3003 (ε r = 3, tanδ = 0.001) with 0.75-mm thickness and copper cladding of 17 μm is used. The components are designed on layer 3 having the thickness of 0.254 mm. Layer 2 is a spacer (RO3003) between MSL component designs and AMC layer. The cross-sectional view of the three-layered design structure is shown in Fig. 3. 1531-1309 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.