Tune-all Wideband Planar Filters for KAT-7

1. Tune-all Wideband Planar Filters for KAT-7 Theunis Beukman Supervisor: Dr. Riana H. Geschke November 2011

2. Outline • Introduction • Motivation • Specifications • Development of a new type of filter • Prototype design & results • Conclusion

3. Motivation • Tolerances in the fabrication processes • Waveguide filters: fine-tune with tuning screws • Microstrip filters: fine-tune with electronic tuning elements • Need for a new filter synthesis consisting of: • Wide bandwidth • Tunable in frequency and bandwidth • Implementable in microstrip

4. Specifications for KAT-7 Filter • Tune-all response (i.e. tunable in f0 & BW) • FBWripple = 49% (1.2 - 1.95 GHz) • ΔLA < 1 dB • LR > 15 dB • s21 ≤ − 20dB: • 0.89 to 1.1 GHz • 2.1 to 2.5 GHz

5. Ring-Resonator Resonance where circumference is n∙λ (n=1,2,3…) Two possible field distributions at resonance Premise is to perturb modes with tuning elements

6. Development of a New Tune-all Filtering-Section Step 1:

7. Development of a New Tune-all Filtering-Section Step 2:

8. Proposed Filtering-Section

9. Design of Complete Filter • Cascade filtering-sections • Increases selectivity • Decreases return loss • Non-tunable matching • Capacitor values chosen from design graphs according to the desired specifications • Design biasing network for the 2 different varactors • Optimise response with closed form microstrip models in MWO • Determine final layout with EM solver

10. Number of Cascaded Sections 1st prototype consist of 4 cascaded sections 2nd prototype consist of 6 cascaded sections

11. Biasing Network

12. Sensitivity of Varactor Diodes Influence of losses on passband: Influence of parasitic inductances on cut-off:

13. Prototype 1: 4 Cascaded Sections Board layout structured with laser Vias constructed with through-hole platting Physical size: 0.54 λg × 1.07 λg

14. Prototype 1: Centred Responses • Fine-tuning the measured response: f0 = 1.53 GHz & FBW = 49%

15. Prototype 1: BW-Tuning Simulated: ΔBW= 17.5% Measured: ΔBW= 24.1% (lower f0 & poor LR)

16. Prototype 1: Frequency-Tuning Simulated: Δf0 = 5% Measured: Δf0 = 6.1% (lower f0 & poor LR)

17. Prototype 2: 6 Cascaded Sections Board layout structured with laser Vias constructed with through-hole platting Physical size: 0.47 λg × 1.69 λg

18. Prototype 2: Centred Responses • Fine-tuning the measured response: f0 = 1.53 GHz & FBW = 49%

19. Prototype 2: BW-Tuning Simulated: ΔBW= 18.8% Measured: ΔBW= 19.8% (lower f0)

20. Prototype 2: Frequency-Tuning Simulated: Δf0 = 8.5% Measured: Δf0 = 8.5% (lower f0)

21. Compare Prototype Filters

22. Advantages and Disadvantages • Advantages: • Wideband • Tunable in f0 and BW • Implementable in microstrip • Low losses • High selectivity • Disadvantages: • Sensitive to parasitic components • Physically large • Poor out-of-band rejection

23. Recommendations Problem: Poor out-of-band rejection in prototype 2

24. Recommendations Solution: Cascade a wider BPF with prototype 2 [2] M. Sanchez-Soriano, E. Bronchalo, and G. Torregrosa-Penalva, “Compact uwb bandpass filter based on signal interference techniques,” Microwave and Wireless Components Letters, IEEE, vol. 19, no. 11, pp. 692 - 694, November 2009.

25. Conclusion Following the literature review, there exists a need for a tune-all wideband filter synthesis A new filter design, based on perturbed ring-resonators, was proposed for KAT-7 specifications The theory was confirmed with fabricated filters This type of filter can also be applied to other wideband specifications such as that of MeerKAT

26. Acknowledgements SKA project for scholarship Sonnet Software for the academic license Applied Wave Research for the academic license Wessel Crouwkamp and Wynand van Eeden, for their help with all the fabrications