# Conductive Ink Printed Fabric Antenna with Aperture Feeding Technique
## 3 Antenna Design  
### Simulation and Fabrication  
The antennas were first designed and simulated in ANSYS Electronics Desktop [16] and then fabricated and measured. Figure 2 shows a prototype of the fabricated antennas and SMA integration concepts for direct and inkjet-printed fabric antennas. A simple square patch antenna is designed to obtain a comparative performance analysis of the two printing techniques at 2.4 GHz. That is the direct/inkjet print method and screen printing.  
The base fabric from the screen printing (polyethylene terephthalate (PET)), is now a conductive fabric sheet measuring 0.12 mm in thickness. This was used for the radiator and ground layer of the patch antenna in Figure 2a. The probe-fed patch antenna is designed with specifications from [17]. The square-shaped radiating patch measures 52 mm on either side. The same material is used for the ground layer which is attached to a 66 mm\({}^{2}\) felt substrate. A 10-micrometer adhesive film bonds the 0.12 mm polyester patch and ground with the 1.0 mm thick substrate. To eliminate and/or minimize geometrical errors, a specialized cutting tool was obtained from Cricut Inc. (Maker 3\({}^{\text{th}}\)) for cutting all fabric materials and adhesive tapes.  
A thin substrate of 1 mm was used to demonstrate a worst-case scenario for a lossy felt substrate. As with all probe-fed patch antennas, the SMA connector is attached to the patch and ground layers using conductive epoxy paste with high silver concentration and fast curing time. The resulting antenna shown in Figure 2a is mildly heated and pressed to ensure maximum bonding of the layers.  
Figure 2: Fabricated antennas showing (**a**) top view of probe-fed patch antenna with conductive polyester base fabric, (**b**) back view of direct printed probe-fed antenna showing SMA attachment (**c**) top view probe-fed antenna with direct printed silver ink.  
Similarly, the direct printed antenna was designed and fabricated by directly injecting and printing the silver ink on a pre-treated felt fabric. The pre-treatment involved thermal pressing at 150 degrees Celsius to ensure an even surface to maximize ink adhesion. The Materpincs SCAG-003 [18] silver-copper-based conductive ink was used with a viscosity of 14,550 mPas and sheet resistivity of 0.05 m\(\Omega\)cm (0.025 m\(\Omega\)/sq), thus achieving bulk conductivity of 0.04 MS/m. The ground plane was printed first and cured at 130 degrees Celsius for 5 min, and then the radiating patch was also printed and cured for the same duration. The direct print resulted in a thicker conductive layer of 0.35 mm compared to the screen-printed method which achieved 0.12 mm thickness. The fabricated model is shown in Figure 2b,c.  
As explained earlier with the differences in the two printing techniques, it was not feasible to use the same inks for the two methods as their printing mechanisms and ink viscosity requirement were different. In addition, to ensure optimum results for each technique, it was necessary to use the best available conductive ink that is optimal for each printing method.  
From Figure 2, each antenna measured 66 mm\({}^{2}\) with a patch size of 52 mm\({}^{2}\). The thicknesses of the antennas were 1.24 mm and 1.7 mm for screen-printed and direct printed methods, respectively. The SMA connector added an extra thickness of 9.5 mm (SMA receptacle length) to both antenna models.