# A Software-Defined Radio Platform for Teaching Beamforming Principles
## 4 Beamforming Platform Validation and Testing
### Beamforming Platform Testing in Indoor and Outdoor Environments  
The functioning of the beamforming system was experimentally verified both indoors (in a laboratory) and outdoors (open area) by performing measurements of the patch antenna radiated pattern in an azimuthal plane. The experimental setup used for indoor measurement of the radiation pattern is present in Figure 14, with a similar setting being deployed outdoors in an open area of 2400 m\({}^{2}\). While controlled measurements in an anechoic chamber were not possible due to resource limitations, this approach was considered suitable for the defined objective, as will be further demonstrated. Due to the close positioning of the measuring probe and the antenna, we can assume that the measured field value is attributed to the antenna under test, allowing for sufficient data collection to understand the basic behavior of beamforming. Additionally, the use of both indoor and  
Figure 13: Measured and simulated S11 (**a**) and S12 (**b**) parameters. outdoor settings gives students a more comprehensive understanding of how beamforming performs under different environmental conditions. For the indoor scenario, the radiation pattern was measured in a 60 m\({}^{2}\) laboratory, for one horizontal plane placed at 90 cm above floor level, in a semicircle with a spatial resolution of \(5^{\circ}\). The patch antenna was connected by RF cables (same type and equal length) to the four TX channels of the USRP. An Aaronia PBSE field probe connected to the USRP RX channel was used for measuring signal strength. The field values were recorded for each azimuthal orientation in a semicircle with a radius of 1 m, considered suitable for the used frequency of 3.53 GHz (\(\lambda\) = 8.49 cm). Two beam orientations were measured: 1. No phase offset between the patch elements (phase values of \(0^{\circ}/0^{\circ}/0^{\circ}/0^{\circ}\)). 2. A phase difference of 45\({}^{\circ}\) between consecutive patch elements (\(0^{\circ}/45^{\circ}/90^{\circ}/135^{\circ}\)). According to Equation (3), the beam steering resulting from the second phase difference would be approximately 20\({}^{\circ}\) for the designed patch antenna. Based on Equation (3), and the maximum measured phase variation of 2.42\({}^{\circ}\), we have calculated a maximum error in the steering angle deviation of 1.01\({}^{\circ}\), which is considered suitable given manual positioning of the E field probe and the spatial resolution of the measurement. The designed graphical user interface presented in Section 2.2 was used to apply the values of the TX channels phase differences. Figure 15 presents the results of the measured radiation patterns in both indoor/outdoor scenarios for two beam orientations: forward \(-90^{\circ}\) and \(20^{\circ}\) tilt \(-\)right. The plotted data were interpolated by a factor of five using a spline function to achieve a better resolution (1\({}^{\circ}\)). Figure 14: Experimental setup for indoor radiation pattern measurement. Figure 15: Indoor/outdoor measured radiation pattern for two beam orientations. First, there is a notable difference in the beam patterns obtained in indoor and outdoor environments. In an indoor environment, there are more reflections and diffraction effects due to walls, furniture, and other obstacles. The multipath propagation occurring in an indoor environment typically results in a more complex or distorted beam pattern compared to outdoor environment. This explains why the small antenna side lobes are not visible for indoor measurements but become visible when the beamforming system is deployed outdoors. We can also observe that path loss is generally lower indoors due to the confined space but tends to fluctuate more due to reflections.