## 1 Introduction  
The large available bandwidth at mm-wave frequencies especially in the 60 GHz band enables new use case scenarios such as the 5G hot-spot proposed for the next generation of mobile communications (5G) [1; 2; 3; 4]. Generally, 5G is expected to bring a revolution to mobile communications: a 1000-fold increase in mobile data traffic and a substantially larger number of connected users per cell [5]. This is to be achieved by using a wider RF bandwidth and greater spectral efficiency as cell size is decreased [1; 2; 3]. These requirements can be met using carrier frequencies in the 57-66 GHz band where a large bandwidth is internationally available. To mitigate the higher free-space path loss in the millimeter-wave range, directive antennas are considered [2; 3; 4; 6]. However, the usage of directive antennas requires beam steering to enable user mobility and multiple independent beams so that multiple users can be supported in dense user scenarios simultaneously. Therefore, steerable directive antennas are a key technology for supporting multiple users in dense user scenarios [3; 6; 7]. Another key technology is optical fiber for fronthauling the high capacity 5G hot-spots and small cells [3; 8]. Radio-over-fiber (RoF) is used as the transport technology between the baseband unit and the antenna for reducing implementation cost and latency through direct optical-to-electrical (O/E)conversion [8]. Thereby, digital-to-analogue conversion and complex signal processing can be avoided. Further benefits of RoF include that it allows for centralizing network functions, which is expected to save cost, especially when a high number of radio access units (RAUs) is considered [3,8]. The application of millimeter-waves for wireless access is investigated intensely with the advent of 5G [2,3] and has already led to prototype devices for 28 GHz phased array beam steering, which are widely discussed and referenced [6]. Despite the technological challenges at higher frequencies, e.g., the 60 GHz band, active phased array beam steering solutions have been reported [7,9]. However, because scaling issues have led to more input ports, greater complexity, and more power consumption, these solutions only support the steering of one beam and a limited baseband signal bandwidth [3,6,7]. Thus, they can only support multiple users within one beam and only use frequency or time division multiple access [7], which limits user experience. Due to these constraints, passive solutions such as lens assisted beam switching or Butler matrix implementations have also been considered [3,10]. While these passive solutions can provide higher signal bandwidth and do not increase power consumption, they still require multiple signal inputs to allow multiple beam operation. Thus, their multi-user support scales poorly, as it requires additional fronthaul capacity and increases the size of the antenna integration. Thus, passive low-cost, multiple-beam solutions, which support a large overall bandwidth, still need to be systematically addressed. For the sake of completeness, it should be noted that the 5G mobile terminals will likely employ different antenna types, as there the vital requirement is to cover all internationally available bands with a very limited form-factor. This emphasizes multi-band operation and wideband coverage in contrast to high gain and beam steering capabilities in base stations. Thus, likely candidates for 5G mobile terminals are printed monopoles for sub 6 GHz 5G and small integrated antenna-on-chip MIMO configurations for mm-wave 5G [11,12]. In this paper, a compact and low-cost substrate-integrated waveguide (SIW) leaky-wave antenna (LWA) for 60 GHz band operation is proposed, and it was used to support multiple users in a 60 GHz hot-spot is proposed. In an LWA, beam steering was achieved by changing the radio frequency (RF) [13,14,15,16]. The fabricated LWA provides 1D H-plane beam steering as well as multibeam operation with 20 GHz operational bandwidth.