Discontinuities modelling and solution

As presented in subsection 4.4.1 the power transmission performance of the CO method is almost the same with the ST model. This is an ideal model assuming that there are no discontinuities (physical gaps) between the two individual modified Stripline parts that are connected together so as to structure the CO interconnection method. In this sub subsection the modelling of the discontinuities via simulations and their effect on the insertion loss (S21) is presented. The simulation models of the parameters (Dx, Dy, Dz) that describe the discontinuities are shown in Fig. 4-18.

Fig. 4- 18 Complementary Overlap discontinuities simulation modelling

The S₂₁ simulation results for various values of the parameters D_x, D_y and D_z are shown in Fig.

4-19. It can be seen that all the discontinuity parameters degraded the power transmission performance, in the case of the CO method. The most sensitive out of all the three discontinuity parameters is the Dz. The CO method is affected by the discontinuities between the two ends of the individual parts of the connected striplines.

NO GAP Dx = 1mm Dx = 5mm Dx = 10mm Dx = 20mm

NO GAP Dy = 1mm Dy = 5mm Dy = 10mm Dy =10.1mm

a)

b)

To ensure better power transmission (less insertion loss) when geometrical discontinuities occur while interconnecting both Stripline parts of the CO structure the ground planes of the longest side (GND) of both individual Stripline parts were extended by 10mm (Fig. 4-20). The simulated S₂₁ results for the D_x, D_y and D_z values with the extended ground plane (EG), for which the non-extended ground plane (NG) yielded S21 lower than -3dB ( Fig.

4-19), are shown in Fig. 4-21.

It can be said that the S21 was improved by the extension of the GNDs in the case of Dx and Dz. The Dy=10.1mm was not improved by the extension of the GNDs. But this value means that the two strips make no contact at all. Regarding the concept of CO in terms of practical application the scenario Dy=10.1mm would be a very rare one. From Fig. 4-19b it can be seen that in a scenario of Dy=10mm, where the two strips have a tangential contact the S21 was kept higher than -3dB. In terms of practical application of CO the Dx and Dz discontinuities are more likely to occur. The choice of enhancing the CO design by extending the GND planes by 10mm, improves the Stripline interconnection method by minimizing the effect of possible connection discontinuities. Regarding the reflection coefficient, when Dx, Dy and Dz occur, it was degraded above -10dB at most frequencies while the discontinuity parameters increased.

The extension of the ground planes improved the reflection coefficient at D_x case at all the examined frequency range. Regarding the Dz and Dy the extension of the ground planes didn’t significantly affect the reflection coefficient.

Fig. 4- 19 Transmission coefficient (S21) simulation results for various values of: a) Dx, b) Dy and c) Dz

NO GAP Dz = 0.3mm Dz = 1mm Dz = 3mm Dz =5mm

c)

Fig. 4- 20 Schematic of CO geometrical discontinuities: a) Dx, b) Dy and c) Dz with extended ground planes

a)

b)

c)

Y X Z

Y X Z Z

X Y

D_x=1mm: NG EG D_y=10.1mm: NG EG Dz=1mm: NG EG

Fig. 4- 21 S₂₁ simulation results of CO discontinuity parameters with (EG) and without (NG) extended ground plane

In terms of practical implementation of the CO the physical discontinuities should be avoided. This is an ideal scenario. The extension of the ground planes is proposed as a solution to minimize the effect of possible occurrence of discontinuities in practical applications (real life scenarios).

Finally, regarding the side shielding, which fulfills the wearable criteria [10] and shielding from other electronics requirement, it was found via simulations that the cases of CO with and without side shielding yielded similar performance.

4.4.3.2 Prototyping and measurements

In terms of evaluating the simulated results (Fig. 4-11) a prototype of the CO model was fabricated using the black felt as dielectric and copper tape for the conductive parts. This prototype was compared with the respective ST (reference) one (Fig. 4-22).

The measured transmission coefficient (S₂₁) and reflection coefficient (S₁₁, S₂₂), of the realized striplines, are shown in Fig. 4-23 and 4-24 respectively. The initial prototype of the CO was fabricated without the extended ground planes. For the case of the CO, appropriate measurement setup by using clamps was followed, so as to minimize the gaps (discontinuities) between two strip lines and achieve almost perfect contact of the two parts of the TLs (as in Fig. 4-26). Additionally, the case without using clamps for the S₂₁ measurement of the CO was examined so as to notice the effect of possible discontinuities occurrence.

Fig. 4- 22 Fabricated ST and CO prototypes of striplines

The clamps minimized the effect of the possible discontinuities, see Fig. 4-23. The case where discontinuities occur, without the use of clamps, seemed to significantly degrade in S₂₁ performance compared with the case where clamps were used. The cases of ST and of the firmly connected CO (with clamps) are in good agreement with simulations (Fig. 4-11). By using the CO method the total stripline model yielded insertion losses less than 0.7dB which is a very promising result in comparison with the 0.5dB insertion losses derived from the ST Stripline model. The reflection coefficient the CO with the clamps case is presented in Fig. 4-24. Both prototypes (ST and CO) yielded S11 and S22 lower than -10dB. Additionally, good two port network symmetry of the realized striplines was noticed as can be seen that S11 and S22 are quite close. It can be said that the CO is a good solution to avoid a coaxial connector, as long as discontinuities are minimized, between striplines in order to transmit power from one stripline to another.

Fig. 4- 23 Measured S21 results of ST and CO prototypes stripline models

Fig. 4- 24 Measured reflection coefficient (S11 & S22) results of ST and CO (with clamps) prototypes stripline models