**4. Integration of the transducer with the divider: experimental results of the Ku-band and W-band power combiners**

The last step in the design is the integration of the mode transducer and the radial divider. Since the return loss levels in both components have been carefully

#### *Electromagnetic Fields and Waves*

controlled, the final optimization of the full power combiner is a simple task only involving a few parameters: the radius of the circular waveguide and the dimensions of the matching cylinders in the divider and in the transducer. After that, the power combiners are manufactured and tested.

#### **4.1 Experimental results of the Ku-band power combiner**

The 16-way radial Ku-band power combiner has been manufactured in brass. **Figure 9a** shows a photograph of the unit during the experimental characterization of the scattering parameters. In the photograph of **Figure 9a**, the combiner has 16 high-precision WR75 matched loads attached to its output ports. The manufacturing has been done in four parts, two halves corresponding to the mode transducer and another two halves corresponding to the radial divider. The cuts separating the parts have been done along the E-plane of the waveguides, in order to reduce the insertion losses.

**Figure 9b** shows the comparison between the simulation and the measurement of the return loss level, under excitation by the input common port. In the inset, the port numbering has been included in a 3D CAD view. The agreement between theory and simulation is excellent, even when the measured value is better than 30 dB in the 11–13 GHz bandwidth. Only a small difference is shown at the upper extreme of the band at 13 GHz.

 **Figure 10a** presents the measured insertion loss of the 16-way combiner compared with i) the theoretical value assuming perfect conductor (σ = ∞, −12.04 dB), and ii) the average value simulated corresponding to the brass conductivity (σ = 15.9·106 S/m, −12.15 dB). From these results, it can be said that the effective conductivity obtained in the manufacturing has virtually achieved the nominal value. The amplitude balance is also very good, since the extreme values are within ±0.15 dB. The phase responses of the transmission from the input to the 16 output ports are shown in **Figure 10b**, with a detail in the inset. The balance between the extreme values is very good as well, within ±2.5o .

**Figure 11a** shows the transmission between two output ports to characterize the isolation. One of the output ports has been selected, the sixth in this case, according to the inset in **Figure 9b**, which represents a generic case because of the rotational

#### **Figure 9.**

*(a) Manufactured Ku-band prototype in the test bench including the high-precision matched loads in the output ports for the experimental testing. (b) Comparison between the simulation and the measurement of the return loss at the input (port 1 in the figure). In the inset, a 3D CAD view shows the port numbers.* 

*Design of Radial Power Combiners Based on TE01 Circular Waveguide Mode DOI: http://dx.doi.org/10.5772/intechopen.82840* 

#### **Figure 10.**

*(a) Measured insertion loss of the 16-way Ku-band combiner compared with the theoretic value assuming perfect conductor (σ =* ∞*, −12.04 dB), and the average value simulated corresponding to the brass conductivity (σbrass = 15.9 MS/m, −12.15 dB). (b) Measured phases of the 16-way combiner from port 1 to ports 2–17, with a detail in the inset.* 

#### **Figure 11.**

*(a) Measured isolation response of the 16-way Ku-band power combiner: Transmission between the output port 6 (see the inset in* **Figure 9b***) and the adjacent output ports of a middle of the combiner, i.e., the S7,6, S8,6, etc. until S14,6 parameter. (b) Comparison between the simulated and measured combining efficiency.* 

symmetry. The graph shows the measured transmission to the adjacent ports: S7,6, S8,6, etc., until the S14,6 parameter. The results for the other parameters related to the other half of the divider would be similar (the simulated results would be exactly equal for a perfectly symmetric combiner). The average value for these eight responses is approximately −14 dB. However, it is interesting to note that the worst case corresponds to the isolation between two contiguous ports, the S7,6 parameter in this case, where the minimum value is close to −6 dB.

In power combiners, a key figure of merit is the combining efficiency parameter [34], defined in (Eq. (2)), using the number 1 for the input common port. It characterizes the combined effect of the deviations of both magnitude and phase with respect to the ideal behavior. **Figure 11b** shows the simulated and measured efficiency, which is better than 95% in the whole operating bandwidth.

$$\mathbf{f}\_{\xi}^{\mathbf{x}} = \frac{1}{N} \left| \sum\_{k=1}^{N} \mathbf{S}\_{k+1,1} \right|^{2} \tag{1}$$

## **4.2 Experimental results of the W-band power combiner**

 The 5-way radial W-band power combiner has been also manufactured in brass [16] by micromachining. The unit has been divided into four parts, which will be stacked vertically. **Figure 12a** shows the CAD view of the parts separated before the assembly, and also after the integration. **Figure 12b** shows a photograph of the combiner during the experimental characterization of the scattering parameters, with high-precision WR10 matched loads.

The comparison between the simulation and the measurement of the return loss level is shown in **Figure 13a**. This is the reflection coefficient seen at the input common port, which is port 6 in the numbering in the inset of the figure. The measured level is better than 20 dB in the complete operation band (12 GHz centered at 94 GHz), and better than 25 dB in the 80% of this bandwidth. These measured levels are coherent with the sensitivity analysis of the power divider taking into account a tolerance for the fabrication of ±0.02 mm.

A systematic process has been followed to characterize the insertion loss of all the transmissions between the common input and the five outputs. According to

**Figure 12.** 

*(a) 3D CAD of the four sections in E-plane configuration to make the 5-way W-band combiner and its final assembly. (b) Manufactured prototype in the measurement bench including the high-precision matched loads in the output ports for the experimental characterization.* 

#### **Figure 13.**

*(a) Comparison between the simulation and the measurement corresponding to the return loss level of the 5-way power combiner excited by the input common port (port 6 in the figure). In the inset a 3D CAD view is shown including the port numbers. (b) Measured insertion loss of the 5-way combiner compared with the theoretical value assuming perfect conductor (σ =* ∞*, −6.99 dB), and the average value simulated corresponding to the brass conductivity (σbrass = 15.9 MS/m, −7.35 dB).* 

*Design of Radial Power Combiners Based on TE01 Circular Waveguide Mode DOI: http://dx.doi.org/10.5772/intechopen.82840* 

#### **Figure 14.**

*(a) Measured phases of the 5-way combiner, with a detail in the inset showing its very small difference. (b) Measured isolation response corresponding to the transmission between output port 1 (see the inset in* **Figure 13a***), and the adjacent output ports of a middle of the combiner, i.e., the S2,1 and S3,1, parameters.* 

#### **Figure 15.**

*Comparison between the simulated and measured combining efficiency of the 5-way W-band power radial combiner.* 

the numbering in the inset of **Figure 13a**, the vector network analyzer is connected between port 6 and the corresponding port from 1 to 5, while the other four ports are connected to high precision matched loads (i.e., with return loss level better than 40 dB at W-band).

**Figure 13b** presents the measured insertion loss of the 5-way combiner compared with the theoretical value assuming perfect conductor (σ = ∞, −6.99 dB), and the average value simulated corresponding to the brass conductivity (σbrass = 15.9·106 S/m, −7.35 dB). The average measured value of −7.6 dB implies that the effective conductivity obtained in the manufacturing is only slightly degraded with respect to the nominal value. The balance for the amplitudes is very good, since it is within ±0.4 dB at the extremes of the band.

The phase response of the transmission between the input and the five output ports is shown in **Figure 14a**, with a difference at the extremes of the band within ±3.5<sup>o</sup> , which also emphasizes the accurate manufacturing for obtaining this reduced margin at this band. **Figure 14b** shows the transmission between two output ports to characterize the isolation. Since the structure is symmetric, a generic port is selected (number 1 in this case, using the numbering in the inset of **Figure 13a**). In consequence, it is simulated and measured the transmission to its adjacent ports,

 i.e., the S2,1 and S3,1 parameter. Their average level is approximately −7 dB, very close to the theoretical value of |η1| = |η2| = |√5/5| in **Table 2**, which is −6.98 dB. Finally, the efficiency has been simulated and measured showing both results in **Figure 15**. The measured efficiency is better than 85% in the whole operating bandwidth.
