CPW Feed to Rectangular Dielectric Resonator Antenna

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CPW Feed to Rectangular Dielectric Resonator
Antenna

• Bratin Ghosh

in collaboration with Yahia M.M. Antar
Department of Electrical and Computer
Engineering, Royal Military College of Canada,
PO Box 17000, Station Forces, Kingston,
Ontario, K7K 7B4, CANADA Aldo Petosa and Apisak
Ittipiboon Advanced Antenna Technology,
Communications Research Centre, 3701 Carling
Avenue, Ottawa, Ontario, K2H 8S2, CANADA
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Outline

• Brief introduction to dielectric resonator
  antenna ( DRA ) and coplanar waveguide ( CPW )
• CPW feed topologies to the DRA
• CPW feed to DRA integrated with Electromagnetic
  Band Gap ( EBG ) structures

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Typical Antenna and Feed
Microstrip patch
Substrate
Microstrip feed
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CPW capacitive feed to the DRA
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Advantages of Dielectric Resonator Antenna ( DRA
) technology

• Low loss compared to planar antennas e.g. the
  microstrip
• Wideband
• High design and fabrication tolerances
• Easy to fabricate
• Low profile

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Advantages of the CPW feed

• Low loss and dispersion compared to microstrip
  feed
• Uniplanar configuration
• Reduced surface wave excitation compared to
  microstrip, especially in electrically thick
  substrates
• Avoid drilling in antenna as required with coax
  feed
• Ideally suited to millimeter wave design
• Ease of active integration
• Do not need vias

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Aim

• Propose an alternate and a more efficient feed
  topology to the DRA based on the CPW, compared to
  the microstrip / coax type feeds
• Examine the effects of the uniplanar feed
  configuration on the radiation characteristics
• Characterize various feed types possible with the
  CPW topology

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CPW feed topologies to the DRA
Circular Loop Feed Kranenburg, Long and
Williams, 1991
Inductive Feed Al Salameh, Antar and Seguin,
2002
Capacitive feed
Square Loop feed
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Capacitive feed Choice of DRA and Slot
dimensions

• Capacitive feed enables electric coupling to the
  DRA, while the inductive feed achieves magnetic
  coupling
• Dimensions of DRA obtained using the Dielectric
  Waveguide Model ( DWM )
• Slot length optimized to obtain maximum coupling
  to the DRA
• Slot width chosen narrow to minimize cross-pol
  levels
• Slot should be totally under the resonator to
  obtain match

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CPW capacitive feed - Dimensions
DRA Ld Wd 10.20 mm, height Hd 7.89 mm and
er 20 RT/Duroid substrate Ls 140 mm, Ws
140 mm, thickness 100 mils, er 10.20 Scap
2 mm, Gcap 1.04 mm, Lcap 6.70 mm, Wcap 0.26
mm
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Field distribution of TEy111 mode in the DRA.
(a) In the xz plane at y0. (b) In the xy plane
at z0.
(a)
(b)
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Return loss characteristics of CPW capacitive
feed to the DRA with slot length Lcap 6.70 mm
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Radiation patterns of DRA at resonance with CPW
capacitive feed and Lcap 6.70 mm
E-plane
H-plane

• E-plane cross-pol 30 dB, H-plane cross-pol
  -16 dB
• Resonant gain 3.6 dBi

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Electric field distribution in CPW capacitive
feed with slot length Lcap 6.70 mm

• Electric field is distributed over the whole
  slot leading
• to the lower frequency resonance

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Return loss characteristics of CPW capacitive
feed to the DRA with slot length Lcap 9.50 mm
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Radiation patterns of DRA at resonance with CPW
capacitive feed and Lcap 9.50 mm
E-plane
H-plane
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• E-plane cross-pol 30 dB ( same as the case
  with Lcap 6.70
• mm ), H-plane cross-pol -11 dB ( slightly
  higher
• than with Lcap 6.70 mm )
• Resonant Gain 5.0 dBi
• Resonant frequencies differ by 14.17,
  controlled by slot length
• Lcap ( all other dimensions of the CPW line
  same )
• Radiation performance and gain comparable to the
  case with
• Lcap 6.70 mm

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Electric field distribution in CPW capacitive
feed with slot length Lcap 9.50 mm

• Electric field is distributed over the trace
  region of CPW leading
• to the higher frequency resonance

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CPW square loop feed to the DRA
Ssq 0.50 mm, Gsq 0.26 mm, Lsq 3.76 mm, Wsq
3.76 mm, Tsq 0.26 mm
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Real estate requirements

• Square loop feed requires 36.12 less space
  than the
• capacitive feed of the smaller dimension, and
  47.80 less
• space than the inductive feed
• Maintaining the same size of the DRA, the square
  loop feed
• can be accommodated on a substrate with lower
  dielectric
• constant
• Reduced surface wave loss with the square loop
  feed,
• specially at millimeter wave frequencies

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Return loss characteristics of CPW square loop
feed to the DRA
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Radiation patterns of DRA at resonance with CPW
square loop feed

• E-plane cross-pol -30 dB, H-plane cross-pol
  -30 dB
• Gain is at 4.1 dBi ( comparable to the
  capacitive feed )
• H-plane cross-pol much lower than the capacitive
  feed due to
• magnetic coupling to the DRA and completely
  symmetric nature of
• feed

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Comparison of feed configurations to the DRA

• Real estate requirements
• Square loop feed 36.12 smaller than the
  capacitive feed of
• the shorter dimension and 47.80 smaller
  than an inductive feed
• Surface wave excitation
• Possible to design the square loop feed on
  a substrate with lower dielectric constant
  leading to reduced surface wave excitation
• Radiation pattern
• H-plane cross-polar levels are much lower in
  square loop feed
• ( below 30 dB ) compared to the capacitive feed

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CPW capacitive, square loop and inductive feeds
to the DRA
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CPW feed to DRA with Electromagnetic Band Gap (
EBG )
structures
DRA 10.20 mm x 10.20 mm x 7.89 mm and er
20 RT/Duroid 6010 substrate 140 mm x 140 mm,
thickness 100 mils, er 10.20 Sind 0.50 mm,
Gind 0.26 mm, Lind 8.20 mm, Wind 0.26 mm, D
8.00 mm, P1 P2 10.44 mm, E 49.76 mm
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EBG configurations

• Case 1 no EBG on CPW ground plane layer
• Case 2 EBG on CPW ground plane layer in the
  form of circular patches of no metallization
• Case 3 EBG on lower layer of substrate in the
  form of circular metallizations, placed at
  identical x and y locations and of identical
  dimensions as Case 2. Additional EBG ( EBG1)
  placed underneath the DRA at x y 0. Specially
  useful when the CPW ground plane layer is used
  for active integration

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Return loss characteristics of CPW fed DRA
without EBG ( Case 1 )

• Good coupling to DRA is achieved with CPW feed

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Radiation pattern without EBG ( Case 1 )
H-plane
E-plane

• Low cross-pol levels are observed due to field
  match between the
• TEy111 mode of the DRA and the CPW feed
• F/B ratio at boresight is at 14.35 dB

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Return loss characteristics of CPW fed DRA with
EBG on CPW ground plane layer ( Case 2 )

• Return loss characteristics not affected by the
  presence of EBG

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Radiation pattern with EBG on CPW ground plane
layer ( Case 2 )
H-plane
E-plane

• F/B ratio at boresight is at 24.76 dB ( much
  improved over Case 1 )
• H-plane back radiation much improved over Case 1
• E and H-plane cross-pol levels are not affected
  by the
• presence of EBG

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Return loss characteristics of CPW fed DRA with
EBG on lower layer of substrate ( Case 3 )

• Return loss characteristics at resonance not
  affected by the
• presence of EBG
• Spurious oscillations off resonance due to
  interference between
• the coupled fields and the central patch

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Radiation pattern with EBG on lower layer of
substrate ( Case 3 )
H-plane
E-plane
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Radiation performance with EBG on lower layer of
substrate ( Case 3 )

• F/B ratio at boresight are at about 26 dB ( much
  improved
• over Case 1, about the same as Case 2 )
• H-plane back radiation much improved over Case
  1and also
• improved over Case 2 large back lobe in Case
  1 effectively
• suppressed
• Central patch ( EBG1 ) specially effective to
  improve back
• radiation performance due to field
  concentration at coupling region
• E and H-plane cross-pol levels are not affected
  by the
• presence of EBG

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Conclusions

• CPW feed offers a uniplanar feed configuration to
  the DRA, in comparison to the microstrip / coax
  feeds
• The advantages of the CPW line, viz. low loss,
  low dispersion, ease of fabrication, active
  integration and reduced surface wave excitation
  over the microstrip line leads to a more
  efficient feed configuration, specially at
  millimeter wave frequencies
• The CPW capacitive feed is characterized by dual
  resonance with 14.17 difference in resonant
  frequencies
• The dual resonance, with comparable radiation
  performance, is determined by the slot length
• The CPW square loop feed offers 36.12 and 47.80
  savings in the real estate over the CPW
  capacitive and inductive feeds respectively

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• The CPW square loop feed can be accommodated
  over a lower
• dielectric constant substrate, leading to
  reduced surface wave loss,
• specially at millimeter wave frequencies
• Radiation performance of the CPW square loop
  feed is much better
• compared to the capacitive feed in terms of the
  H-plane cross-pol

CPW fed DRA with EBG

• F/B and back radiation characteristics much
  improved, specially in
• the H-plane
• Very easy to fabricate
• Can be incorporated either on the CPW ground
  plane layer or on the
• lower layer of substrate, with comparable
  performance
• For the latter case, the central EBG patch
  underneath the DRA
• ( EBG1 ) is specially effective in suppressing
  the H-plane back lobe
• The latter design also enables CPW active
  integration on the ground
• plane layer
• Return loss, E and H-plane cross pol levels
  unaffected by EBG

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Thanks