Theunis BeukmanSupervisor: Dr. Riana H. Geschke

November 2011

TUNE-ALL WIDEBAND PLANAR FILTERS FOR KAT-7

OUTLINEIntroduction

– Motivation– Specifications

Development of a new type of filterPrototype design & resultsConclusion

MOTIVATIONTolerances 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 FILTERTune-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 GHz2.1 to 2.5 GHz

RING-RESONATORResonance where circumference is n∙λ

(n=1,2,3…)Two possible field distributions at

resonancePremise is to perturb modes with tuning

elements

DEVELOPMENT OF A NEW TUNE-ALL FILTERING-SECTION

Step 1:

DEVELOPMENT OF A NEW TUNE-ALL FILTERING-SECTION

Step 2:

PROPOSED FILTERING-SECTION

DESIGN OF COMPLETE FILTERCascade filtering-sections

– Increases selectivity– Decreases return loss

Non-tunable matchingCapacitor values chosen from design graphs

according to the desired specificationsDesign biasing network for the 2 different

varactorsOptimise response with closed form

microstrip models in MWODetermine final layout with EM solver

NUMBER OF CASCADED SECTIONS1st prototype consist of 4 cascaded sections2nd prototype consist of 6 cascaded

sections

BIASING NETWORK

SENSITIVITY OF VARACTOR DIODES Influence of losses on passband:

Influence of parasitic inductances on cut-off:

PROTOTYPE 1: 4 CASCADED SECTIONSBoard layout structured with laser Vias constructed with through-hole

plattingPhysical size: 0.54 λg × 1.07 λg

PROTOTYPE 1: CENTRED RESPONSESFine-tuning the measured response:

f0 = 1.53 GHz & FBW = 49%

PROTOTYPE 1: BW-TUNINGSimulated: ΔBW = 17.5%

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

PROTOTYPE 1: FREQUENCY-TUNINGSimulated: Δf0 = 5%

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

PROTOTYPE 2: 6 CASCADED SECTIONSBoard layout structured with laser Vias constructed with through-hole

plattingPhysical size: 0.47 λg × 1.69 λg

PROTOTYPE 2: CENTRED RESPONSESFine-tuning the measured response:

f0 = 1.53 GHz & FBW = 49%

PROTOTYPE 2: BW-TUNINGSimulated: ΔBW = 18.8%

Measured: ΔBW = 19.8% (lower f0)

PROTOTYPE 2: FREQUENCY-TUNINGSimulated: Δf0 = 8.5%

Measured: Δf0 = 8.5% (lower f0)

COMPARE PROTOTYPE FILTERS

ADVANTAGES AND DISADVANTAGESAdvantages:

– 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

RECOMMENDATIONSProblem: Poor out-of-band rejection in prototype

2

RECOMMENDATIONSSolution: 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.

CONCLUSIONFollowing 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

ACKNOWLEDGEMENTSSKA project for scholarshipSonnet Software for the academic licenseApplied Wave Research for the academic

license Wessel Crouwkamp and Wynand van

Eeden, for their help with all the fabrications