# Fully Metallic Additively Manufactured Monopulse Horn Array Antenna in Ka-Band
## 4 Experimental Validation  
The prototype of the difference pattern horn array antenna, manufactured using additive techniques, underwent measurement and experimental validation at the University of Oviedo, Spain. Initially, scattering parameters were assessed using the Agilent N5247A PNA-X vector analyzer to ensure proper functionality. The reflection coefficient comparison with CST Microwave Studio [35] is depicted in Figure 4. The maximum measured reflection coefficient is \(-10.8\) dB. Despite minor variations, primarily due to manufacturing tolerances, i.e., \(\pm 50\) \(\upmu\)m, the measured results below \(-10\) dB closely align with simulated data, validating the performance of the device. Once the reflection coefficient was successfully validated, radiation pattern measurements were carried out. Firstly, the prototype of the difference pattern horn array was placed in the anechoic chamber (spherical range) of the University of Oviedo, Spain. In Figure 5a, an image of the measurement setup for the anechoic chamber is depicted. The normalized radiation patterns for the main planes (\(\phi=0^{\circ}\) and \(\phi=90^{\circ}\)) at 36 GHz are illustrated in Figure 6 for both copolar (CO) and crosspolar (CX) Linear Polarized (LP) field components. In addition, values from a full-wave numerical simulation are compared with measurements, with dashed lines for \(\phi=0^{\circ}\), dotted lines for \(\phi=90^{\circ}\), and solid lines for simulations. Figure 3: Photographs of the additively manufactured difference pattern horn array antenna in AlSi10 Mg. Figure 7 displays the measured normalized radiation pattern for CO in the U-V plane at 34, 35, and 36 GHz compared with simulations. Additionally, the results show that the measured level for the null of the copolarized component with respect to the maximum is \(-27\) dB at 36 GHz, with SLLs remaining below \(-10\) dB. More importantly, the level in the null of the radiation pattern was accurately measured for different frequencies. Figure 8 presents the measured level in the center of the radiation pattern from 32 to 36 GHz compared with the simulated value. It is important to note the frequency squint that happens around the center of the pattern due to electrical dimensions. A minimum value of \(-48.4\) dB is measured at 33 GHz. Figure 4: Scattering parameters of difference pattern horn array prototype, comparing measured (_solid lines_) with simulated (_dashed lines_) results with \(\pm 1\%\) deviation in shadow. Figure 5: The measurement setup for the additively manufactured horn array prototype in **(a)** the spherical range in an anechoic chamber and **(b)** the planar acquisition range. Figure 6: Normalized radiation pattern of difference pattern horn array prototype at 36 GHz, comparing measured (_dashed and dotted lines_) with simulated (_solid lines_) results. Figure 7: _Cont_. Furthermore, the prototype was also measured in the planar acquisition range at the University of Oviedo, Spain. The picture in Figure 5b illustrates the prototype of the difference pattern horn array antenna mounted in the measurement setup in a planar acquisition range in a semianechoic environment. The setup comprises an open-ended waveguide in the Ka-band, used as a near-field probe. Both the probe and the prototype are connected to an Agilent N5247A PNA-X vector analyzer. Then, a 100 \(\times\) 100 mm\({}^{2}\) plane is measured at 95 mm from the center of the antenna to obtain most of the radiated power. The grid is sampled every mm from 32 to 38 GHz. This measurement campaign is used to evaluate the phase difference in the aperture. In Figure 9, near-field measurements are illustrated, both in amplitude and in phase, for frequencies of 34, 35, and 36 GHz. Remarkably, in Figure 9a,c,e, amplitudes are shown with a null in the central part for the cut \(x=0\), corresponding to the center of the aperture.