# Research on Penetration Loss of D-Band Millimeter Wave for Typical Materials
## 1 Introduction  
The rapid growth of mobile data and the use of smartphones have created an unprecedented challenge for wireless service providers to overcome the global bandwidth shortage [1, 2]. To address this challenge, there is growing interest in cellular systems in the 30 to 300 GHz millimeter waveband, which has a much wider bandwidth available than today's cellular networks [3, 4]. Some high frequency bands (mm-band) were previously used for satellite communications, long-range point-to-point communications, military communications, and LMDS (28 GHz), but short wavelengths make it impossible for waves to bypass, or have quasi-optical propagation characteristics [5], which means that the high frequency bands do not have the rich scattering characteristics of the sub-6 GHz band [6, 7, 8, 9, 10]. Under line-of-sight conditions, the received signal energy is concentrated on the line-of-sight and a few low-order reflection paths. Under the condition of non-light of sight, signal propagation mainly relies on reflection and bypass, resulting in sparse channels in space and time, and the occlusion of people or objects will lead to large signal fading. High-band channels have many characteristics that are significantly different from sub-6 GHz cellular mobile channels [11, 12, 13, 14]. The development of new 5G systems that can operate in higher frequency bands requires accurate propagation models for these frequency bands. Industry trends at home and abroad show that 5G mmWave is the next stage of 5G development, but it will require a significant amount of time and R&D costs to address the propagation characteristics of mmWave, before it can be deployed as a more general wireless network solution. Millimeter waves propagate in space as directional waves, have good directivity, are easily blocked by obstacles, and lack penetrating power. Channel measurement and modeling work has also been carried out for high frequency bands, for example, Aalto University in Finland has carried out measurement activities in 15, 28, 60 GHz and E-bands(81-86 GHz) based on a 60 GHz VNA detection system and completed multi-point conference room measurements to obtain the extended SV channel model [15]. Using the VNA measurement system, Ericsson participated in the METIS, mmMAGIC and 5 GCM projects and completed the following several measurements: (1) in indoor 60 GHz transmission human blocking experiments [16], it was found that the human blocking loss can also be as high as 10-20 dB; (2) with indoor multi-frequency medium and long-range path loss measurements, it was observed that the bypass is the main path of millimeter-wave indoor non-light of sight transmission [16; 17]; (3) multi-frequency under NLOS conditions in urban blocks. The measurement found that the signal path loss does not depend on the frequency very much, and is lower than the result of the knife-edge bypass, indicating that the signal in the case of outdoor NLOS mainly comes from other reflection paths [17]. (4) The final measurement was multi-band measured wall penetration loss [18]. In the 5 GCM project, Nokia and Aalborg University in Denmark collaborated on path loss measurements at 10 GHz and 18 GHz [18]. The mm MAGIC project has other measurement activities [17], such as (1) French Telecom Orange Lab (Belfort) completed multi-frequency O2I measurements to observe penetration loss as a function of frequency; (2) French CEA-LETI completed 83.5 GHz and other indoor propagation channel measurements. In April 2019, Verizon, the largest mobile operator in the United States, launched 5G mobile services in the 28 GHz band in Chicago and Minneapolis. For indoor coverage, Verizon's 5G mmWave signal is nearly unreachable. After penetrating the concrete wall, the 5G download rate dropped sharply from 600 Mbit/s to 41.5 Mbit/s, while the 4G downlink rate at 1900 MHz did not change much, due to the severe penetration loss of 5G mmWave.