## 4 Experimental Results
The other measured characteristics of both resin-based filters are similar to aluminum-based prototype and initial design specifications (Table 1). The advantage of the 80 g resin-based prototype is that it is 2.6 times lighter than its aluminum-based one (208 g). Table 5 compares various GGW bandpass filters with the wideband GGW Chebyshev filters manufactured in this work. The order \(n\) or number of cells of the GGW filters [30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45] reported in Table 5 varies between two and seven, and almost half of them are of order five, as are the proposed GGW filters. The structures were mainly manufactured by means of a CNC milling machine, except for two [36; 41] that also used a 3D printing technique. The  
Figure 13: EM simulated and measured 5-parameters for the conductive paint metallized resin-based fifth-order wideband GGW Chebyshev filter (Figure 8c). different designs cover the bands X to W (8 GHz-110 GHz). Half of them are distributed in the low X and Ku bands (8 GHz-18 GHz) as the proposed design. As can be seen in Table 5, unlike the proposed design method and [45], which can achieve wideband responses (\(FBW>10\%\)), the other filters developed are narrowband (\(FBW<4\%\)), since they were obtained from resonant cavities [30; 31; 32; 33; 34; 35; 36], coupled resonators [37; 38; 39; 40; 41; 42], evanescent wave coupled resonators [43], and periodic corrugations acting as resonators [44], which can only work in a narrow bandwidth. The wideband response of the proposed GGW bandpass filter design was obtained by combining the high-pass behavior of the GGW with the low-pass characteristic of the metallic pins placed along the groove area of the GGW, acting as impedance inverters. Contrary to [45], a rigorous synthesis method based on stepped impedances was applied to the metallic pins to obtain the desired higher cutoff frequency (\(f_{c,H}\)) of the passband. The three manufactured wideband GGW bandpass prototypes present high performance in the passband and rejection band with respect to the other GGW filters. Except the resin-based GGW prototype metallized with a conductive paint spray (Figure 13) that has \(RL=15\) dB and \(IL=1.2\) dB, the other two wideband GGW filters (Figures 11 and 12), based on aluminum and resin coated with a silver layer, exhibit better \(RL\) and \(IL\) than most of the filters reported in Table 5. In addition, the maximum level reached in the stopband (\(RLSB\)) is similar to the highest values obtained with the narrowband filters. The three fabricated prototypes did not require any post-manufacturing tuning, since the sensitivity to the mechanical tolerance is lower than bandpass filters based on high-\(Q\) resonators. It should also be noted that the metallic pins along the groove area of the GGW, which are properly centered, distributed, and sized according to a stepped impedance technique, allow the implementing of compact wideband Chebyshev GGW filters. The designed fifth-order wideband GGW filter has a first-order normalized area of \(0.53\lambda_{0}^{2}\). In Table 5, this area is, respectively, 1.4 and 9.9 times less than the smallest [45] and largest [33] GGW bandpass filter.