Tune all wideband planar filters for kat 7
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Tune-all Wideband Planar Filters for KAT-7. Theunis Beukman Supervisor: Dr. Riana H. Geschke November 2011. Outline. Introduction Motivation Specifications Development of a new type of filter Prototype design & results Conclusion. Motivation. Tolerances in the fabrication processes

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Tune-all Wideband Planar Filters for KAT-7

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Tune all wideband planar filters for kat 7

Tune-all Wideband Planar Filters for KAT-7

Theunis Beukman

Supervisor: Dr. Riana H. Geschke

November 2011


Outline

Outline

  • Introduction

    • Motivation

    • Specifications

  • Development of a new type of filter

  • Prototype design & results

  • Conclusion


Motivation

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


Specifications for kat 7 filter

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


Ring resonator

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


Development of a new tune all filtering section

Development of a New Tune-all Filtering-Section

Step 1:


Development of a new tune all filtering section1

Development of a New Tune-all Filtering-Section

Step 2:


Proposed filtering section

Proposed Filtering-Section


Design of complete filter

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


Number of cascaded sections

Number of Cascaded Sections

1st prototype consist of 4 cascaded sections

2nd prototype consist of 6 cascaded sections


Biasing network

Biasing Network


Sensitivity of varactor diodes

Sensitivity of Varactor Diodes

Influence of losses on passband:

Influence of parasitic inductances on cut-off:


Prototype 1 4 cascaded sections

Prototype 1: 4 Cascaded Sections

Board layout structured with laser

Vias constructed with through-hole platting

Physical size: 0.54 λg × 1.07 λg


Prototype 1 centred responses

Prototype 1: Centred Responses

  • Fine-tuning the measured response:

    f0 = 1.53 GHz & FBW = 49%


Prototype 1 bw tuning

Prototype 1: BW-Tuning

Simulated: ΔBW= 17.5%

Measured: ΔBW= 24.1% (lower f0 & poor LR)


Prototype 1 frequency tuning

Prototype 1: Frequency-Tuning

Simulated: Δf0 = 5%

Measured: Δf0 = 6.1% (lower f0 & poor LR)


Prototype 2 6 cascaded sections

Prototype 2: 6 Cascaded Sections

Board layout structured with laser

Vias constructed with through-hole platting

Physical size: 0.47 λg × 1.69 λg


Prototype 2 centred responses

Prototype 2: Centred Responses

  • Fine-tuning the measured response:

    f0 = 1.53 GHz & FBW = 49%


Prototype 2 bw tuning

Prototype 2: BW-Tuning

Simulated: ΔBW= 18.8%

Measured: ΔBW= 19.8% (lower f0)


Prototype 2 frequency tuning

Prototype 2: Frequency-Tuning

Simulated: Δf0 = 8.5%

Measured: Δf0 = 8.5% (lower f0)


Compare prototype filters

Compare Prototype Filters


Advantages and disadvantages

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


Recommendations

Recommendations

Problem: Poor out-of-band rejection in prototype 2


Recommendations1

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.


Conclusion

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


Acknowledgements

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


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