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

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





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



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)



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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