# Conductive Ink Printed Fabric Antenna with Aperture Feeding Technique
## 5 Measurement and Result Discussion  
The fabricated antenna models (BLE ad LoRa) are measured to validate the aperture-coupled feed technique with coaxial cable and that of the modified patch structure. Figure 8c shows the anechoic chamber setup for the LoRa antenna model. The results presented in Figures 9-12 show excellent gain and return loss performance, nearing that of a regular PCB microstrip patch. Figures 9 and 10 show the simulated and measured \(S11\) of the BLE and LoRa models, respectively. With a measured impedance bandwidth of 82 MHz (2.40-2.482 GHz) at \(-10\) dB \(S11\) shown in Figure 9, the measured BLE model operates well within the 2.44 GHz band. The LoRa model result shown in Figure 10 is measured at \(-10\) dB \(S11\) from 853-885.5 MHz, representing 32.5 MHz bandwidth, also operating within the LoRa band. Both models are comparable to the simulated results with minimal differences. The success of the correlating results was a result of using very precise cutting tools, minimal epoxy application, and low-loss adhesive film. The conductive epoxy adhesive can significantly affect the impedance performance when not applied and cured properly. Figure 10, for instance, shows slightly improved results in the 511 of the measured data compared with the simulated. This among other reasons stated already may also be due to the marginal inaccuracies of representing the dielectric coefficient, conductivity, and loss tangents of the newly created conductive materials used in these models. Further discussions on this are shown in [4,9]. Figure 10: S11 curve of LoRa aperture-fed antenna (868 MHz center frequency). Figure 9: \(S11\) curve of BLE aperture-fed antenna (2.44 GHz center frequency). Figures 11 and 12 show the normalized radiation patterns in the \(yz\) and \(xz\) planes of the BLE and LoRa models, respectively. A measured antenna gain of 3.85 dBi at 56.1% radiation efficiency (\(\eta_{\textit{eff}}\)) is recorded at 2.44 GHz. The simulated gain was obtained at 5.1 dB, representing a 1.25 dB drop in measured gain. A front-to-back (FBR) of better than 9.35 dB (\(\approx-5.5\) dB back radiation) is recorded in both planes and HPBW of 78.8 deg. and 73.76 deg. is recorded in the \(yz\) and \(xz\) planes, respectively. With the LoRa model, an antenna gain of 3.9 dBi is measured at 868 MHz with \(\eta_{\textit{eff}}\) of 44.92%. The simulated gain was obtained at 3.5 dB. A front-to-back (FBR) of better than 20.62 dB (\(\approx-16.7\) dB back radiation) is recorded in both planes. Measured HPBW is observed at 87.6 deg. and 73.4 deg. for \(yz\) and \(xz\) planes, respectively. The BLE model in particular resulted in an FBR of 9.35 dB compared with the LoRa with 20.62 dB. Although comparable to some aperture-coupled antenna results shown in Table 3, this may be attributed to the higher fringing radiations in the \(yz\) plane resulting in increased surface currents on the ground plane. The smaller patch size of the BLE model thus resulted in a larger back lobe radiation. This can be corrected by increasing the ground size of the antenna and/or the substrate thickness. Conversely, the minimized back lobe observed in the LoRa model shows the performance improvement of this feeding technique over the traditional aperture-fed patch antenna with suppressed back lobe. Figure 11: Normalized radiation patterns of aperture-fed antenna (2.44 GHz). Figure 12: Normalized radiation patterns of aperture-fed antenna (868 MHz). The cable placement on the antenna ground layer had minimal effect on the radiation pattern. However, some distortions in the pattern can be observed especially in the _xz_ plane of the LoRa model and both planes of the BLE. The patterns show a dip between theta 90 to 120 degrees which is the plane on which the cable is laid. An effective suggestion might be to use thinner cables with a higher grade of shielding; both of which were expensive and inaccessible to the researchers in the course of the design. Another area of concern was the cross-polarization (x-pol.)