## 1 Introduction  
Millimeter waves (MMW) are considered for short-range wireless links for Fifth-Generation (5G) cellular communications. This will increase channel capacity and channel availability. New bands in the MMW spectrum are already allocated, mainly in the vicinity of 28 GHz [1; 2; 3; 4]. In addition to the growth in cellular communications, the rising popularity of autonomic vehicles has accelerated development in automotive radars, which are based on millimeter wave technology [5; 6].  
Currently, a common method to analyze signal propagation in tunnels or corridors uses modal expansion [7; 8; 9; 10]. In this approach, the tunnel is treated as an empty waveguide, and the field in the cross-section is expressed as a summation of the transverse Eigenmodes above the cutoff frequency. However, at high frequencies such as those of the millimeter wavelengths, the method becomes ineffective. The transverse dimensions are much larger than the wavelength, and too many modes are required to be considered. In such an overmoded scenario, the calculation will be inaccurate, and the modal approach is no longer useful.  
An alternate method to deal with indoor propagation is by solving the Maxwell equations in a numerical computational solver, imposing boundary conditions to calculate the field along the tunnel. In large structures, the computation becomes time consuming, requiring large storage and computing capabilities, and its resulting accuracy is limited to the numerical calculation resolution [11; 12].  
Due to its short wavelength, the propagation of MMW can be analyzed using \"quasi-optical\" models. The wavelength is much smaller than the cross-section dimensions, and the indoor multi-path can be treated using ray-tracing, providing significant advantages compared to propagation modeling [13; 10; 14; 15]. The ray-tracing model has high resolution and is easy to implement on any computer without the need for special storage or computing capabilities.  
Compared to the \"conventional\" RF bands in the VHF and UHF, the MMW band faces more implementation challenges [16; 17]. Millimeter waves suffer from atmospheric attenuation, are affected by scattering and absorption, and are specularly reflected by surfaces. Nevertheless, the potential of MMW communication is important. In addition to its free spectrum, it is useful for densely packed communication networks due to its small equipment and antennas, and it offers frequency reuse potential due its to directivity and atmospheric attenuation.  
This research focuses on the implementation of ray tracing in the analysis of indoor millimeter wave propagation. The MMW antennas are frequently directional, and their radiation pattern must be considered. It is shown that the radiation pattern of the transmitting and receiving antennas plays a role in the indoor multipath that emerges due to the occurrence of multiple reflections. It is important to note that, although the use of ray-tracing in the analysis of millimeter waves' propagation is both effective and reliable, it is necessary to determine how many rays should be considered in the simulations. The accuracy of the multi-ray model is examined for different scenarios, including omni-directional and directive transmissions. The study is employed to demonstrate a millimeter wave link operating in frequencies allocated for the 5G cellular communications. Experimental verification is conducted and the results compared to the simulation model results.  
The objective of this work is to study the propagation of millimeter wave transmission along corridors (or tunnels), comparing between communication scenarios of omni-directional links, as well as directive ones. Theoretical analysis is done for expressing the transfer function (magnitude and phase) of a wireless MMW link in both cases. The model is used for calculating the power budget and dispersive group delay emerging due to the involved multi-path phenomenon.