## 3 Results  
A prototype of the ESICL continuous profile filter was manufactured and measured. The filter was designed to have the stop band centered at 11 GHz. This led to \(\Lambda=13.52\) mm. For the sinusoidal variation of the coupling coefficient, the values \(A_{k}=50\), \(n_{p}=15\) and \(\theta=0\) were used, which are the values used in Section 2. Therefore, the coupling coefficient is the one depicted in Figure 2, the variation of the impedance is the one shown in Figure 3, and the width of the inner conductor is the one plotted in Figure 6. The other dimensions of the ESICL cross section are \(B=2.618\) mm, \(A=6\) mm, \(t=0.866\) mm. With all these values, the simulated insertion losses at the central frequency are 37.8 dB, and the fractional bandwidth is 23.8%. The prototype was manufactured with Rogers 4003C substrates of height \(h=0.813\) mm, with electrodeposited copper foils of 17 \(\upmu\)m, and substrate permittivity \(\varepsilon_{r}=3.55\). The manufactured prototype is shown in Figure 8. The manufacture of the ESICL filter follows standard processes of planar circuit manufacturing (drilling, milling, and electrodeposition). First, the ESICL via holes were drilled and the lateral walls were cut. Then, the substrate was metallized using electroplating. This metallized the via holes and the lateral walls. Next the accessing planar lines and the transitions were milled. Finally, all the layers were piled together using alignment screws,  
Figure 7: Influence of the design parameters (\(A_{k}\) and \(n_{p}\)) on the stop band response of the ESICL filter (insertion losses and fractional bandwidth). and soldered using tin soldering paste. An LPKF Protolaser U3 circuit board plotter was used for the drilling, cutting, and milling. An LPKF Mini Contac RS through-hole electroplating system was used for electroplating, and an LPKF ProtoFlow S reflow oven was used for curing the tin soldering paste. Figure 9 compares the simulated and measured scattering parameters of the ESICL prototype. As can be observed, there is a very good agreement between the simulation and measurements. One of the advantages of continuous profile filters is supposed to be the high tolerance to manufacturing errors. In order to verify this low sensitivity to variations in the dimensions of the filter, the scattering parameters of the ESICL prototype were simulated altering the width on the inner conductor (\(w(z)\)). This dimension is the most critical dimension of the filter, since this is the dimension that has a greater influence on the impedance of the ESICL. Taking into account the manufacturing tolerance of the machine used for drilling and cutting (50 \(\upmu\)m), the scattering parameters were simulated with the nominal value of \(w(z)\), with \(w(z)\) increased by 50 \(\upmu\)m, and with \(w(z)\) decreased by 50 \(\upmu\)m. The results are shown in Figure 10. As can be observed, the response of the filter did not change significantly after either increasing or decreasing \(w(z)\), which is consistent with the alleged advantage of this type of filters. Finally, the performance of the continuous profile filter of Figure 8 in the ESICL was compared with the same filter implemented in microstrip technology. Figure 11 shows the simulated results for this filter in both technologies. Lossy copper (conductivity \(\sigma=5.8\cdot 10^{7}\) S/m) and lossy dielectric (\(\varepsilon_{r}=3.55\), \(\tan\delta=0.0027\)) were considered in the simulations. The simulations were obtained using CST. These simulations estimated a quality factor of the ESICL filter of 1547, whereas for the microstrip filter, the estimated quality factor was 348. The reflection coefficient \(S_{11}\) at the central frequency (11 GHz) was -0.04 dB for the ESICL filter, and -0.91 dB for the microstrip filter. The total length of the filter was 20.3 cm in the ESICL, and 12.2 cm in the microstrip. Figure 8: Manufactured prototype of the ESICL continuous profile filter. Figure 9: Simulated and measured scattering parameters of the manufactured ESICL filter prototype.