_Article_  
Bandwidth Improvement in Bow-Tie Microstrip  
Antennas: The Effect of Substrate Type and  
Design Dimensions  
[PERSON] 1, [PERSON] 2,3,5 [PERSON] 2, [PERSON] 4,  
[PERSON] 5, [PERSON] 6, [PERSON] 6 and [PERSON] 2,* (c)  
Footnote 1: [[http://www.mdpi.com/journal/applsci](http://www.mdpi.com/journal/applsci)]([http://www.mdpi.com/journal/applsci](http://www.mdpi.com/journal/applsci))  
Footnote 2: [[https://www.mdpi.com/journals/article/pdf/10.0002/10](https://www.mdpi.com/journals/article/pdf/10.0002/10)]([https://www.mdpi.com/journals/article/pdf/10.0002/10](https://www.mdpi.com/journals/article/pdf/10.0002/10)).  
a bow-tie antenna that was used in GPR applications [18]. They adjusted the parameters of the antenna to change its equivalent capacitance and inductance, while it was tuned to operate in the frequency range from 0.5 to 1.2 GHz, thereby realizing an ultra-wideband antenna. Very recently, [PERSON] and [PERSON] proposed a novel wideband cylindrical conformal antenna for global positioning system (GPS) applications by using a wide slot in the ground plane, incorporating a bow-tie-shaped patch antenna [19]. The effect of graphene conductive ink on the performance of bow-tie-shaped antenna was also studied by [PERSON] et al. [20]. It was seen that the developed design is well compatible for applications in LTE, WiMAX and Wi-Fi. In 2019, another bow-tie antenna was designed by [PERSON] and [PERSON] for entire band application of GPS (L5), PCS, IMT-2000, Bluetooth, Wi-Fi, WiMAX bands, and part of ultra-wide band (UWB) frequency range [21]. In order to utilize bow-tie type UWB antennas [PERSON] et al. in [22] designed a balun which is integrated into the antenna.  
In the current research work, three different bow-tie-shaped microstrip antennas are designed, fabricated and experimentally tested. The first and second batch of the devices is fabricated on different thicknesses of RT 5880 substrate. Simulations and experimental results of the first batch showed that the antenna is well matched and the S11 is about 37 dB. The antenna is a single band operating at 7 GHz with 0.7 GHz (6.7 GHz-7.4 GHz) impedance bandwidth. The second batch is also printed on RT5880 materials with different substrate thickness. It was noticed that higher thickness provided relatively wider bandwidth, which is around 0.9 GHz (6.7 GHz-7.6 GHz), and the percentage bandwidth was increased from 10% to 12.5%. The third design is suggested to show a broadband application of bow-tie-shaped antenna. In the third batch, 1.4 GHz bandwidth was obtained. All of the three designs are under the UWB band and can be used for different microwave applications. From the results of the paper, it was found that the smaller thickness provides wider bandwidth with lower gain. Therefore, the thickness and relative permittivity of the substrate can be selected based on the application. It means the substrate thickness and type can be used to control obtained gain and bandwidth. This work can be used as a practical guide that can help researchers to view substrate selection as a method to control antenna performance (gain, bandwidth, polarization). This point can be considered as the novelty of this work, which may not have been seen before.  
As is generally known, the design of a slotted bow-tie antenna depends on the applications and if it is working in frequency or time domain. In frequency-domain applications, slots are often used in a bow-tie antenna to increase the antenna bandwidth [23; 24; 25]. In this case, two parameters are of importance--namely the slot width and location. The slot dimensions, which is another novel side of this study, are chosen especially for the required bandwidth and gain.  
The rest of this paper is organized as follows: In Section 2, the design of bow-tie-shaped microstrip antennas is presented, while the fabrication process of the antennas are presented in Section 3. Further, the simulation and experimental results along with discussion are given in Section 4, and the main conclusions are drawn in Section 5.