Theunis Beukman Supervisor: Dr. Riana H. Geschke November 2011

O UTLINE Introduction – Motivation – Specifications Development of a new type of filter Prototype design & results Conclusion

M OTIVATION 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

S PECIFICATIONS FOR KAT-7 F ILTER Tune-all response (i.e. tunable in f 0 & BW) FBW ripple = 49% ( GHz) ΔL A < 1 dB L R > 15 dB s 21 20dB: 0.89 to 1.1 GHz 2.1 to 2.5 GHz

R ING -R ESONATOR Resonance where circumference is nλ (n=1,2,3…) Two possible field distributions at resonance Premise is to perturb modes with tuning elements

D EVELOPMENT OF A N EW T UNE - ALL F ILTERING -S ECTION Step 1:

D EVELOPMENT OF A N EW T UNE - ALL F ILTERING -S ECTION Step 2:

P ROPOSED F ILTERING -S ECTION

D ESIGN OF C OMPLETE F ILTER 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

N UMBER OF C ASCADED S ECTIONS 1 st prototype consist of 4 cascaded sections 2 nd prototype consist of 6 cascaded sections

B IASING N ETWORK

S ENSITIVITY OF V ARACTOR D IODES Influence of losses on passband: Influence of parasitic inductances on cut-off:

P ROTOTYPE 1: 4 C ASCADED S ECTIONS Board layout structured with laser Vias constructed with through-hole platting Physical size: 0.54 λ g × 1.07 λ g

P ROTOTYPE 1: C ENTRED R ESPONSES Fine-tuning the measured response: f0 = 1.53 GHz & FBW = 49%

P ROTOTYPE 1: BW-T UNING Simulated: ΔBW = 17.5% Measured: ΔBW = 24.1% (lower f 0 & poor L R )

P ROTOTYPE 1: F REQUENCY -T UNING Simulated: Δf 0 = 5% Measured: Δf 0 = 6.1% (lower f 0 & poor L R )

P ROTOTYPE 2: 6 C ASCADED S ECTIONS Board layout structured with laser Vias constructed with through-hole platting Physical size: 0.47 λ g × 1.69 λ g

P ROTOTYPE 2: C ENTRED R ESPONSES Fine-tuning the measured response: f0 = 1.53 GHz & FBW = 49%

P ROTOTYPE 2: BW-T UNING Simulated: ΔBW = 18.8% Measured: ΔBW = 19.8% (lower f 0 )

P ROTOTYPE 2: F REQUENCY -T UNING Simulated: Δf 0 = 8.5% Measured: Δf 0 = 8.5% (lower f 0 )

C OMPARE P ROTOTYPE F ILTERS

A DVANTAGES AND D ISADVANTAGES Advantages: – Wideband – Tunable in f 0 and BW – Implementable in microstrip – Low losses – High selectivity Disadvantages: – Sensitive to parasitic components – Physically large – Poor out-of-band rejection

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

R ECOMMENDATIONS 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 , November 2009.

C ONCLUSION 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

A CKNOWLEDGEMENTS 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