Car Rooftop Antenna for Satellite Radio Reception

1
Car Rooftop Antenna for Satellite Radio Reception

• Team 26
• Joe Banasiak
• Jeremy Seuring

2
Introduction

• Satellite radio currently operates from 2.32 to
  2.345 GHz
• Two companies offer this service
• Sirius 2.32-2.3325 GHz, 12.95/month
• XM 2.3325-2.345 GHz, 9.99/month
• XM uses geostationary satellites with a line of
  site of about 30 deg. above the equator
• Sirius uses geosynchronous satellites (elliptical
  orbits) with a line of site of about 60 deg.
  above the equator
• Both companies use terrestrial repeaters which
  are used to carry signal where buildings block
  satellite signals

3
Objective

• Our goal is to create low-profile antennas for
  both satellites and terrestrial repeaters
• Design of a loop antenna for receiving the
  vertically (linear) polarized terrestrial signal
• Design of an array of microstrip patches for
  receiving the LHCP satellite signal
• We will incorporate phase shifting in our array
  to demonstrate beam steering capabilities

Block Diagram
4
Design Goals

• Frequency of operation from 2.32-2.345 GHz
• Satellite antenna gain of at least 2 dBi over
  elevation angles 20 to 90 degrees
• Demonstrate beam steering over elevation angles
• Satellite antenna needs to receive circular
  polarization
• Terrestrial antenna gain of at least -1 dBi from
  0 to 20 degrees elevation
• Terrestrial antenna needs to receive linear
  polarization

5
Terrestrial Antenna - Loop

• Loop Antenna
• The loop antenna is ideal for keeping the
  design of our antennas low-profile

• Theory
• Loop antennas emit the desired endfire pattern
  for loops with a diameter of roughly ?/10.

• Problems
• For our frequency, the diameter would be 1.29 cm,
  this makes fabricating the antenna extremely
  difficult
• Wire radius needs to be small compared to loop
  size

6
Terrestrial Antenna - Monopole

• Solution
• We decided to compromise our low-profile design
  by using a monopole antenna

• Theory
• Input reactance of dipoles is minimized when the
  length of the dipole is about 0.5?, 1.5?, 2.5?,
  etc. This is desired to make the antenna
  efficient
• Image Theory
• Introducing a ground plane caused an image of the
  antenna above the ground plane to be created
  below the ground plane
• This allows for monopole antennas of half the
  length of a dipole antenna, that look like the
  dipole.
• The input impedance of the monopole will be ½ the
  input impedance of the dipole
• The gain of the monopole will be twice the gain
  of the dipole

7
Terrestrial Antenaa - Monopole
L0.75?

• Typical patterns of a monopole
• We wish to have a pattern that has a wide endfire
  beam, so the desired length of our monopole is
  0.25?

L0.25?
L1.25?
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Terrestrial Antenna - Monopole

• Simulations Ansoft HFSS9
• We simulated our monopole antenna with different
  lengths of the monopole around ?/4 to find the
  best length of the monopole
• The ground plane needed to be at least ?/2 on
  each side to be effective, so we chose 8 cm.

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Terrestrial Antenna - Monopole

• Once simulations were complete, we plotted S11
  for each monopole length and compared to find
  optimal length

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Terrestrial Antenna - Monopole

• Fabrication
• Cut ground plane and drilled a hole in its center
• Place SMA connector with the probe feed and
  dielectric through the hole in the ground plane
• Soldered the SMA connector to the underside of
  the ground plane, and cut the dielectric flush
  with the top of the ground plane
• Solder additional length of wire to probe, to
  make the monopole longer than anticipated length
• Connect monopole to Network Analyzer and cut the
  length of the monopole down so S11 is minimized
  in our frequency range

11
Terrestrial Antenna - Monopole

• After fabricating the monopole, and looking at
  S11, we determined S11 wasnt low enough
• We decided making the ground plane larger may
  improve S11, so we re-simulated and found that a
  ground plane with each side 16cm improved S11
  dramatically

Ground plane length 16 cm
Ground plane length 8 cm
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Radiation Pattern Test Set-up

• We obtained our radiation patterns using the
  anechoic chamber, the HP 8510 Network Analyzer,
  and 959 Spectrum v2.1 software
• The anechoic chamber is a room with special
  padding that absorbs electromagnetic radiation,
  ensuring that the signal received by the gain
  horn comes directly from the antenna
• We tested our antennas by rotating them 360
  degrees in three different planes
• Azimuthal plane (x-y)
• Elevation angle 0 degrees plane (y-z)
• Elevation angle 90 degrees plane (x-z)

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Terrestrial Antenna - Monopole

• Simulations results vs Testing

lt- Simulated -gt
lt- Tested -gt
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Terrestrial Antenna - Monopole

• Fields, simulated vs tested

E(?)
E(?)
E(f)
E(f)
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Terrestrial Antenna - Monopole

• Overall specs
• Maximum Gain 4.822 dBi
• HPBW 50 degrees
• Gain greater that -1dBi over elvation angles
  -12 lt ? lt 72
• Better than the specification of 0 lt ? lt 20
• Greater than 90 of power accepted over frequency
  range
• Input Impedance (59 j5)O

16
Design of Patch Antenna Theory and Materials

• Patch antennas resonate at ?e/2, but must be
  designed shorter to account for fringing fields
• The type of feed and feed location will affect
  the input impedance of the patch antenna
• Feed location also determines types of EM
  polarizations radiated and received

• Actual dimensions of patch depend effective
  permittivity of the substrate
• Increase in er decreases size, but increases
  surface waves
• Increase in dielectric thickness increases
  bandwidth
• Decided on er 2.2 (Rogers Duroid 5880) with
  thickness 3.175 mm based on tradeoffs and
  available materials

17
Design of Patch Antenna Simulation and
Optimization
Initial Design

• Used an available program to find general
  starting points for a matched feed position
• Constructed square patch with side length of
  40.8mm and feed position of 13 mm from nearest
  sides (such that the feed position is located on
  the diagonal of the square)
• Simulated in HFSS over the range 2.3-2.6 GHz
• S11 plot shows that the patch does not reach true
  resonance
• VSWR is above 2 over the operating band which
  results in less than 90 of the incident power
  entering the patch

S11 of Original Patch
dB
Freq (GHz)
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Design of Patch Antenna Simulation and
Optimization
Optimized Design
Initial Design

• Set up an optimization in HFSS to find the best
  feed point and side length for resonance and
  matching
• Varied side length and feed point
• Compared Smith charts, S11 plots, and VSWR plots
  of the results to obtain optimized patch
• Determined side length of 40.3 mm and feed
  position of 15.25 mm to be optimum design
• VSWR under 1.4 over entire operating band results
  in over 97 of input power entering patch

• Used an available program to find general
  starting points for a matched feed position
• Constructed square patch with side length of
  40.8mm and feed position of 13 mm from nearest
  sides (such that the feed position is located on
  the diagonal of the square)
• Simulated in HFSS over the range 2.3-2.6 GHz
• S11 plot shows that the patch does not reach true
  resonance
• VSWR is above 2 over the operating band which
  results in less than 90 of the incident power
  entering the patch

S11 of Optimized Patch
S11 of Original Patch
Under -15 dB over entire operating band
dB
dB
Resonance at 2.33 GHz (midband)
Freq (GHz)
Freq (GHz)
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Design of Patch Array Theory

• Why choose an array?
• Arrays allow an increase in gain and beam
  steering capability
• Why a 3 x 3 array?
• Beam direction capabilities increase with the
  number of elements, but so does complexity of
  feed network. A 3 x 3 will allow us to attempt
  beam steering while still having fairly simple
  power combination
• Array Spacing
• Half wavelength spacing allows for minimization
  of sidelobes in array pattern
• Array equation
• Pattern Multiplication
• Multiply the array factors and element pattern to
  find radiation pattern

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Design of Patch Array Fabrication

• Build
• Weve shown single patch works, simulator ran out
  of available memory when attempting to simulate
  full 3 x 3 array
• Used HFSS geometry to program milling machine to
  mill out 3 x 3 array on Rogers Duroid 5880
  dielectric
• Drilled feed points and soldered a coaxial feed
  to each element

• Power Combination
• Nine elements - one feed
• Used one 2 to 1 and two 8 to 1 power combiners
  made available by Prof. Bernhard
• Problem Power dividers are very expensive, and
  most are very wideband, the ones we used worked
  for 2-18 GHz (we only need 2.32-2.345 GHz)
• Solution For this array to be produced the most
  effective solution is to custom design a 9 way
  power split.

Wilkinson Power Divider
Can extend 2-way split to either binary tree or a
N-way split
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Design of Patch Array Test Results
Network analyzer results for patch resonance and
coupling

• Typical S11 -15 dB at 2.3325 GHz
• Typical coupling for adjacent patches -17 dB
• Typical coupling for diagonal patches -23 dB

(Reflection)
(Adjacent Coupling)
(Diagonal Coupling)

• More than 90 power accepted over entire
  operating band
• 97 power accepted at 2.3325 GHz

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Design of Patch Array Test Results
Max Gain 10.2 dBi Axial Ratio 1.4 dB Side Lobe
Level -5 dBi HPBW 30 degrees
E(?)
E(f)
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Design of Phase Shifter Theory

• Original Plan To purchase phase shifters for the
  antenna elements to demonstrate beam steering
  ability
• Problem Phase shifters are very expensive and we
  would need 9 of them. Most phase shifters cover
  a large bandwidth
• Solution Build phase shifting lines for 3
  discrete steering angles

• Chosen Steering Angles
• ? 70, f 0 (Along the x-axis)
• ? 30, f 90 (Along the y-axis)
• ? 70, f 30 (Off-axis)

The necessary element phasing can be calculated
with the following equation
knm -k(ndsin(?)cos(f)mdsin(?)sin(f))

• n is the element position along the x-direction
• m is the element position along the y-direction
• d ?o/2

• The delay lines were designed with lengths to
  match the calculated delays
• Converted from delay length in radians to
  centimeters
• Originally set reference element line length to
  ?e
• HFSS gave inaccurate results due to length of
  line, redesigned lines with reference length ?e
  /2

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Design of Phase Shifter Simulation Fabrication

• Simulated phase lines in HFSS, made necessary
  corrections
• After final simulations all phase lines within 1
  degree of desired phase length
• Fabricated the lines with three lines to a feed
  and left connection gaps so we could solder the
  corresponding line for each beam steering
  direction

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Design of Phase Shifter Testing
X-axis lines
Network analyzer results
Desired Phase Delay
Y-axis lines
Network analyzer results
Desired Phase Delay
Off-axis lines
Network analyzer results
Desired Phase Delay

• X-direction lines in proper range or off by
  similar relative phase
• Y-direction lines differ more, but are off by
  relatively similar values
• Off-axis results far from desired ? did not test
  radiation pattern

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Design of Phase Shifter Testing X - Direction
Radiation Patterns in dBi
Max Gain 8.2 dBi Axial Ratio 2.1 dB Side Lobe
Level 0 dBi HPBW 34 degrees
E(?)
E(f)
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Design of Phase Shifter Testing Y - Direction
Max Gain 9.4 dBi Axial Ratio 2.1 dB Side Lobe
Level -5 dBi HPBW 35 degrees
E(?)
E(f)
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Function Test

• We ordered an XM radio tuner and connected our
  antennas to it
• The microstrip array antenna received well
• The array needed to be pointed toward the south
  to pick up a signal.
• On our demo day, we were located at Everitts
  shipping doors. We noticed that we were able to
  receive a signal when the array was pointed
  toward Talbot Lab, showing that the satellite
  signal was being reflected.
• Monopole antenna performed well
• We were able to pick up a signal, with almost any
  orientation of the antenna on a clear day when
  not surrounded by buildings. This demonstrated
  the monopoles large beam width.

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Cost Analysis
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Recommendations

• Build narrow band power dividers to reduce the
  cost of the antennas
• Steer beam by mechanical means rather than using
  phase shifters
• To steer beam effectively, need many different
  phase shifts
• Would allow smaller array or single element
• Design different layout of patches so that beam
  steering is not needed
• Requires circuitry to select the appropriate
  patch
• Gain of each patch needs to be large enough
• Encase antenna in material such as radome to
  shrink the size
• Construct housing for antenna for protection

Thanks to Prof. Bernhards group for materials
and guidance Special thanks to Greg Huff