# A Dual-Band Modified Franklin mm-Wave Antenna for 5G Wireless Applications
## 1 Introduction
Researchers have worked on several modifications of this antenna to obtain improved antenna parameters. One such work is demonstrated in [14], where it is used for radar application. Here, the conventional Franklin antenna is modified for automotive short-range radar applications in which the phase-shifting sections are arranged in a simple straight-line configuration. It is again restricted to a single band operation with less bandwidth. Another variation of the Franklin antenna is presented in [15], which is used for wireless charging applications. The design is complex, as it consists of 32 elements arranged in a collinear array pattern. Since it is designed for wireless charging applications, the frequency of operation is low. A 14 element Franklin antenna was proposed in [16]. The advantage of this design was that a simplified feeding technique was introduced, which gave rise to a more longitudinally and transversely compact class of antennas. A circularly polarized Franklin antenna is demonstrated in [17], where it finds its application in radars. Here the 12 elements are arranged circularly to obtain a circular class of Franklin antenna. The design provides high inter port isolation and moderate impedance. All these antennas were limited to narrowband operation, and in [18], a modified Franklin antenna was introduced where the upper and lower cut off frequencies are designed based on the patch length and stub length. The six-element array antenna generated a wide bandwidth over a single resonant frequency. In [19], the Franklin antenna was developed on dielectric slab to operate at single band of operation. Here, the meander-based geometry is used to obtain high impedance phenomenon at the desired single band resonance. The designed antenna is powered by standard and surface waves along with a dielectric structure, in such a way that the energy is gradually radiated. Finally, in [20],the design that was used for the multi-band response was modified to obtain a single band operation. The design was modified in such a way that additional uniform slots were introduced in the ground plane. This enabled the antenna to resonate at a single frequency with a suitable bandwidth. Even though this antenna results in a large bandwidth as well as gain, the drawback was that it was limited to a single frequency of operation. All of the collinear array antennas and Franklin antennas that were designed earlier faced certain drawbacks, such as the single/dual resonant frequency with narrowband operation, limited bandwidth, low directive pattern, and complex structure. Due to these issues, it may be difficult for them to be integrated with portable wireless devices for modern wireless communication systems. In this paper, the proposed antenna introduces the concept of a Franklin antenna that has been modified in such a way to obtain a wideband antenna resonating at two different frequencies i.e., 22.7 and 34.9 GHz. The proposed antenna is designed in four steps. In the first step, the Franklin radiator is designed by utilizing a 3 \(\times\) 3 unit cell array structure with full ground plane. This structure resulted in four mmW bands with poor impedance matching at the first three bands. So, in order to overcome this problem, the ground plane is etched with a one-by-three array slot format in the second step. This modification also resulted in triple band operation but with poor impedance matching at the first two bands. In the third step, the slot configuration at the ground part is modified in the form of a two-by-three array, while keeping the radiator unchanged. This configuration resulted in dual band operation with S\({}_{11}\) very close to \(-10\) dB, at both bands. Finally, in the fourth step, in order to get the desired wide bandwidth and good impedance matching with dual band operation (i.e., at 22.7 and 34.9 GHz), the ground part is further etched with a slot configuration of a three-by-three array. A detailed parametric investigation is also carried out to fix the dimension of the proposed design.