and high gain planar array a suspended stripline feeding

BGU

Band and High Gain Planar Array Wide BGU

with a Suspended Stripline Feeding NetworkNetwork

N Daviduvitz U Zohar and R Shavit

Dept. of Electrical and Computer EngineeringB G i U i i f h N I l

N. Daviduvitz, U. Zohar and R. Shavit

Ben‐Gurion University of the Negev, Israel

ANTENNAS MINI‐SYMPOSIUMANTENNAS MINI‐SYMPOSIUM July 30, 2012

Faculty of Engineering, Tel Aviv University

OutlineBGU

• Motivation

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• Suspended Substrate Stripline

• Radiating Element Design

• Feeding Network Design• Feeding Network Design

• Antenna Array Analysis

• Comparison to other feeding networks

C l i• Conclusions

Motivation and Previous WorkBGU

Motivation

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Motivation• In many wireless applications, single element antennas are unable to meet the gain and radiation pattern requirements and an antenna array is necessary.

• The feeding network complexity and length, decrease the array ffi i d i f di d l iefficiency and gain for medium and large size arrays.

• A feeding network with low losses is an important factor in theenhancement of the gain and radiation efficiency.enhancement of the gain and radiation efficiency.

Previous Work on the subjectR.N. Simons, "A Millimeter‐Wave Cavity‐Backed Suspended Substrate Stripline Antenna”, IEEE Antennas and Prop Inter Symp Dig vol 3 pp 2110‐2113 1999IEEE Antennas and Prop. Inter. Symp. Dig.,vol 3, pp. 2110 2113, 1999.

Suspended Substrate StriplineBGUBGU

Physical LayoutThe suspended substrate stripline consists of a strip conductor of width w and of a strip conductor of width w and thickness h printed on a dielectric substrate of thickness d. The substrate is suspended inside a grooved metal channel of width ainside a grooved metal channel of width aand height b.

Suspended Stripline Main Advantages

Cross section of the suspended substrate stripline

Suspended Stripline Main Advantages• Low losses due to thin dielectric sheet ‐ r=3.66 ,tan=0.004.• Wide band support due to TEM mode propagation.• Small dimensions compared to standard waveguides, which allows compact

design.• No coupling between suspended stripline adjacent lines.• No radiating losses from the feeding network.• No surface wave losses.

Radiating ElementBGU

Physical LayoutThe radiating element consists of a shorted

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The radiating element consists of a shorted cylindrical waveguide fed by a metallic strip supported by a thin dielectric substrate thus f i b Th b i th t i fforming a probe. The probe is the extension of the suspended stripline and is inserted into the waveguide through a rectangular opening in the waveguide wall.

Design Guidelines• The waveguide supports only TE mode• The waveguide supports only TE11 mode

propagation.• Impedance matching is achieved by

f h d d lRadiating element

optimization of the suspended striplinefeeding probe parameters L and w and its distance, Bt from the short.

• EM simulation performed using HFSS commercial software.

Radiating ElementBGUBGU

h l

Return loss of the radiating element as a function of frequency

Description Physical Size

Waveguide radius R 10 mm

Probe length L 5.34 mm

Probe width w 0.6 mm

Distance to aperture Tp 26.5 mm

Di t t h t Bt 6 05

Radiating element

Distance to short Bt 6.05 mm

Optimized physical dimensions of the radiating element

Radiating ElementBGUBGU

Copol and Xpol of the radiating element at the center frequency

Radiating element gain as a function of frequency element at the center frequency

of 10GHzfrequency

Parameter ValueGain (10GHz) 8.63 dBi( )Main lobe direction 0 deg.

94 deg.62 d

Single element radiation parameters

62 deg.Rad. efficiency (10GHz) 0.9934

Suspended Substrate Stripline and Microstrip BGU

Mi i M i Di d

ComparisonBGU

Microstrip Main Disadvantages1. High transmission losses as frequency goes up2. Radiation losses3. Mutual coupling to adjacent lines Cross section of a microstrip line

Comparison of the insertion loss of a 1cm suspended stripline and a microstrip line

Parameter StudyStriplineSuspended Substrate BGUBGU

Characteristic impedance of SSL as a function of the metal strip width at the center frequency of 10GHz

Cross section of suspended substrate stripline

Insertion loss at the central frequency of 10GHz as a function of the metal strip width

Feeding NetworkBGU

Design Guidelines• Low loss operation based on the

suspended stripline analysis

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suspended stripline analysis.• Injected power (amplitude and phase)

divides evenly among the 16 radiating l telements.

• Main lines characteristic impedance Z0=41 and element impedance 22.

Electric field distrib tion in a cross section ofElectric field distribution in a cross section of the transmission line


Transmission line width a 1.6 mm

Transmission line height b 0 8 mmTransmission line height b 0.8 mm

Metal strip width w 1 mm

Metal strip thickness h 0.03 mm

Feeding networkDielectric sheet thickness d 0.2 mm

Feeding Network AnalysisBGUBGU

Feeding network HFSS design

Phase difference of the two output ports of the T‐junctions as a function of frequency

Amplitude difference of the two output ports of the T‐junctions as a function of frequency

Mutual Coupling Between Array ElementsBGUBGU

Type 2 Elements Type 1 Elements

Type of elements due to mutual coupling considerations

Real and imaginary parts of type 1 elements Real and imaginary parts of type 2 elements

Antenna ArrayBGUBGU

4x4 element array geometry


Array length 9.4 cm

d h

Parameter ValueGain (10GHz) 20.41 dBiMain Lobe Direction 0 degArray width 9.4 cm

Antenna height 3.3 cm

Spacing between 2 35 cm ( ~ 0 8 λ0 )

Main Lobe Direction 0 deg.16 deg.16 deg.Spacing between

elements center2.35 cm ( 0.8 λ0 )

Antenna array physical and electrical parameters

-12.8 dB

Antenna ArrayBGUBGU

Copol and Xpol array radiation patternsArray gain as a function of frequency Copol and Xpol array radiation patterns at the center frequency of 10GHz

Array gain as a function of frequency

Array return loss as a function of frequency

Array radiation efficiency as a function of frequency

Boxed Stripline Feeding NetworkBGU

Boxed Stripline Design Guidelines

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Boxed Stripline Design Guidelines• The boxed stripline consists of a strip conductor boxed inside a waveguide.• In order to check the SSL feeding network efficiency, a similar array was

designeddesigned.• Junction and element matching principals were kept in order to efficiently

split the energy among the elements.

Cross section of a boxed stripline designed with HFSSdesigned with HFSS

StriplineSuspended –Hybrid Waveguide Feeding Network BGUFeeding Network

The hybrid feeding network

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The hybrid feeding networkThe inner slits in the power divider weredesigned to help distribute the phase evenlyamong the 4 output portsamong the 4 output ports.

Hybrid array top view


Type 1 slit depth 12.1 mm

Type 1 slit width 0.05 mm

Type 1 slit distance to input 21.05 mmType 1 slit distance to input 21.05 mm

Type 2 slit depth 5.36 mm

Type 2 slit width 0.1 mm

1 to 4 power divider top view

Type 2 slit distance to input 4.5 mm

1 to 4 power divider physical parameters


Coax to Suspended Stripline

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TransitionDue to physical size limitations, the 4 group element T‐junction was redesigned and the 4 Group Junction HFSS Designelement T junction was redesigned and the coaxial line is matched to excite each 4 group element evenly.


Coax inner radius 0.32 mm

C di 0 78Coax outer radius 0.78 mm

Coaxial line physical parameters

Phase difference of the two output ports of the T‐junction as a function of frequency

Amplitude difference of the two output ports of the T‐junction as a function of

frequency


Coax to Waveguide Transition• The a eg ide ph sical si e as selected

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• The waveguide physical size was selectedto support single mode propagation at afrequency of 10 GHz.

• The coaxial line was matched to theshorted waveguide to decrease losses asmuch as possible. Cross section of the waveguide and theCross section of the waveguide and the

coaxial lineDescription Physical Size

Waveguide height b 7 mmWaveguide height b 7 mm

Waveguide width a 19.3 mm

Coax inner radius extension L1 1.1 mm

Matching section size L2 4 mm

Matching section radius R2 0.625 mm

Distance from short d 3 9 mm(~0 13 λ0)

Coaxial to waveguide transition physical parameters

Distance from short d 3.9 mm( 0.13 λ0)

Return loss as a function of frequency


4 to 1 Power Divider• The waveguide width physical size forced

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g p yfeeding network to become a 4 to 1 power divider.

• The power divider is excited through a coaxialThe power divider is excited through a coaxial line inserted through the bottom and distributes the power evenly, amplitude and phase to the 4 output ports 4 to 1 power divider side viewphase, to the 4 output ports. 4 to 1 power divider side view

Phase difference between the 4 ports of the power divider as a function of frequency

Amplitude distribution to the 4 ports of the power divider as a function of frequency

Comparison of Arrays Parameters with Different BGUFeeding Networks BGU

Return loss of the arrays as a function of frequency

Array gain as a function of frequency

Comparison of Arrays Parameters with Different Feeding Networks

BGUg

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Parameter Suspended Stripline

Hybrid Array Boxed Stripline Array

Microstrip Line Feeding Network

Array with Patch Element Array

Max Gain (dBi) 20.41 20.46 19.53 18.04

Rad. Efficiency (10GHz)

0.923 0.927 0.76 0.55

Height (mm) 33 49 33 ~ 3 6Height (mm) 33 49 33 ~ 3.6

Manufacturing complexity

Moderate High Moderate Easy

Array 4x4 parameters comparison

Comparison Conclusions• The hybrid array is the most efficient in comparison to other arrays but the• The hybrid array is the most efficient in comparison to other arrays, but the

manufacturing complexity and the added height is a major disadvantage.• The microstrip line array is the simplest array to manufacture, but it lacks in

radiation efficiencyradiation efficiency.• The suspended stripline array is a good compromise in manufacturing complexity

and radiation efficiency.

C l i BGUConclusions BGU

• The performance of a 4x4 array with SSL feeding network was analyzed and optimized to obtain:

• Radiation efficiency of 91% in the frequency band 9.6‐10.7GHz.Radiation efficiency of 91% in the frequency band 9.6 10.7GHz.• Gain of 20.41 dBi at the central frequency (10 GHz).• ‐10dB return loss bandwidth of 1.08GHz (11% bandwidth) around the

central frequency (10 GHz)central frequency (10 GHz).• An improvement of 15% in radiation efficiency and 0.8 dB in gain was obtained

compared to a similar array based on boxed stripline feeding network.• The SSL feeding net ork is simpler to fabricate and pro ides better radiation• The SSL feeding network is simpler to fabricate and provides better radiation

efficiency in comparison to the boxed stripline and the hybrid waveguide feeding networks.

and high gain planar array a suspended stripline feeding

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