# A Dual-Band Modified Franklin mm-Wave Antenna for 5G Wireless Applications
## 1 Introduction  
The evolution of mobile standards from the first generation (1G) standard to the fifth generation (5G) standard, where we currently stand, and the future standards is considered as a revolution in the field of wireless communications. It all began with 1G, where the basic calling facility was introduced with no proper coverage and security for the network. 2G networks changed the whole concept with the introduction of a messaging facility or short message system as well as with digital voice calls and encryption of the calls. The second-generation network laid the foundation for all wireless communication networks. The introduction of 3G, or the packet-switched networks improved data rates, increased data transfer capability, as well as the introduction of video calls for applications such as video streaming and video conferencing revolutionized the mobile standards [1]. Fourth-generation (4G) networks are currently the most popular network standard in the present world. The transition from the previous standard to the present standard required various infrastructure changes to the antenna as well as the other equipment such that it can become 4G compatible. All the above standards face a common problem, which is the scarcity of bandwidth. The 5G standard or the internet of things era is the solution thatovercomes this problem. 5G technology requires new infrastructure that has to be laid for the implementation. It is a mature technology that has proven to be of high data rate communication [2; 3]. The wireless spectrum that exists presently is losing its free space, which has led to researchers exploring the unused millimeter-wave (mmW) spectrum for such applications [4]. Millimeter wave technology exploits the frequency spectrum from 30 to 300 GHz. The wavelength required for the operation of mmW varies from 10 to 1 mm. The advantages of using the above technology include high data rates, almost the same as those obtained in optical fibers, achieved at a lesser cost or free of cost [5; 6]. The added merits to this technology are that at high frequencies, the traffic is less, and the communication would be more secure because these frequencies cannot be utilized by everyone. The drawbacks are that a completely modified infrastructure has to be laid out for obtaining these higher frequencies [7; 8]. Proper substrate selection is needed with an appropriate value of dielectric constant, while the thickness of the substrate also plays an important role in the deployment of this technology. mmW technology deals with frequencies in the range of GHz, so the conventional single-antenna structures might fall short of the requirements such as high gain, directive patterns, and bandwidth. So, the need of combining of antenna structures to form array structures is required. Among the different types of antenna array structures, one of the array types is the collinear array (CoA) antenna. A series of antenna elements that are fixed in such a manner that they are parallel and located along a common axis is termed a collinear antenna array. This antenna principle is further modified and applied to a new antenna termed Franklin antenna [9]. In a Franklin array antenna, in addition to the antenna patch elements that are placed in a collinear manner, two transmission lines are placed in between the patches as well as a phasing stub assembly. High gain is a feature of these antennas. The restriction of these classes of antennas is that they are mainly restricted to a single band of operation [9; 10; 11]. Several researchers showed interest in the collinear array principle of antennas in improving the various antenna parameters. A simple arrangement of collinear microstrip patch antenna is illustrated in [12; 13], which was limited to a single band operation with a high gain. The narrowband, along with single-band operation, was the limitation of this antenna. Various modifications of the collinear array antenna were introduced, of which the Franklin antenna is an example.