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© Antenova 2009 Integrated Antenna and RF Solutions Commercial in Confidence
Tuneable antennas for UHF-TV reception
Brian Collins, Devis Iellici and Vijay Nahar
Antenova Ltd, Cambridge Adaptable and tuneable antenna technology for handsets and
mobile computing products
IET, Savoy Place, 22nd October 2009
© Antenova 2009 Integrated Antenna and RF Solutions Commercial in Confidence
Overview
In this presentation we will examine: § The performance requirements for UHF-TV antennas
for portable devices § The potential performance advantage of tuneable
antennas § The selection of tuning techniques § Three examples of tuneable antennas for handset and
Notebook platforms.
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Performance requirements
MBRAI Specification for DVB-T/H (EICTA) Mobile Broadband Radio Air Interface European Information & Communications Technology Industry Association
This says, of the antenna solution in a small hand held terminal: § “Current understanding of the design problem indicates that the typical
antenna gain at the lowest UHF-band frequencies would be in the order of –10dBi increasing to –5dBi at the (upper) end of UHF-band. Nominal antenna gain between these frequencies can be obtained by linear interpolation.”
§ Similar words are used in ETSI TR 102 377 V1.4.1 (Jun 2009)
§ There is no “specification” – the more gain we can obtain from the mobile antenna, the better the system will function.
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Gain and coverage
Impact of antenna gain on effective coverage EBU, [5]
Relative radial distance
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Why tune the antenna?
Prototype 15x50mm antenna on 200x300 PCB
0
10
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470 520 570 620 670 720 770 820
F(MHz)
Effic
ienc
y (%
)
Fo=470Fo=510Fo=540Fo=585Fo=630Fo=685Fo=750Fo=850Specification
Gain suggested in 8 fixed tune points ETSI TR 102 377
Fully tuneable
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Smaller platforms
First prototype 15x50mm antenna on 200x100 PCB
0
10
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470 520 570 620 670 720 770 820
F(MHz)
Effic
ienc
y (%
)
Fo=470
Fo=610
Specification
Fo=860
First prototype 15x50mm antenna on 120x70 PCB
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470 520 570 620 670 720 770 820
F(MHz)
Effic
ienc
y (%
) Fo=470Fo=480Fo=860SpecificationFo=610
As usual, an effective antenna depends on the presence of chassis currents and design becomes more challenging as the platform becomes smaller
200 x 100mm
120 x 70mm
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Constraints on a tuneable design
§ Loss – The antenna will be electrically small, so losses are
very important, especially at the bottom of the band § Tuning range
– With almost an octave to cover, the tuning system requires a very wide tuning range
§ Voltage and power available for tuning are severely constrained, especially in a handset (typically <3V and a few µA).
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Tuning technology
§ MEMS capacitor arrays / MEMS switches+caps – Latest technology – High stray C to ground – Significant losses – High voltage required – Reliability/hysteresis?
§ PIN diode switches + capacitors – Lossy
§ GaAsFET switches + capacitors – Lossy.
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Tuning technology
§ BST capacitors (barium strontium titanate) – Lossy – Require high voltage
§ Varactor diodes – Mature technology – Available for 4/6 volt operation – Some types have low ESR (0.25 ohms) – Problem with Cmin if we want large Cmax.
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Circuit arrangement
§ Conventional tuning circuits: – Capacitively top-load radiating element – Provide matching circuit between antenna
and receiver
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One new solution
§ Varactor diodes, directly/indirectly coupled to radiator – High ratio Cmax/Cmin (7) , connected in series
to reduce Cmin – Linear voltage doubler circuit to control from
RX § Tuning driven by C/N ratio from the receiver
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Fixed-tuned reference design
§ Unconventional order of connections for an inverted-F antenna § Dimensions reduced by more use of meandering § Tuning by capacitive patches on FR4 substrate
– Reasonably independent tuning/coupling controls § Note small adjustment increments! § The following efficiency measurements relate to this geometry.
15mm x 50mm 470-860MHz
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Tuneable design
§ Planar version of the current antenna with tuning varactors and DC coupling inductors
§ The tuning capacitor is on the left and the coupling capacitor on the right.
15mm
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Compact tuneable antenna
§ Folded or radiator to suit space requirements of application
§ Red wires connect tuning voltages to varactor diodes.
10mm
5mm
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Tuneability
0 10 25 50 100 200
-100j
-50j
-25j
-10j
10j
25j
50j
100j
∞
∇ 1
∇ 2
MARKERS: MHz Ω
CH21.S1P1: 470 36.2+19.3i2: 478 33.6-20.2i
0 10 25 50 100 200
-100j
-50j
-25j
-10j
10j
25j
50j
100j
∞
∇ 1
∇ 2
MARKERS: MHz Ω
CH68.S1P1: 846 58.2+13.3i2: 854 39.5+4.6i
Impedance plots for the complete prototype with fitted varactor diodes at channel center frequencies of 474MHz, 658MHz and 860MHz. The effect of reduced bandwidth at lower frequencies is clearly seen.
0 10 25 50 100 200
-100j
-50j
-25j
-10j
10j
25j
50j
100j
∞
∇ 1
∇ 2
MARKERS: MHz Ω
CH44B.S1P1: 654 59.7+21.4i2: 662 35.1-9.2i
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Matching
§ In this design, there is no antenna matching circuit ─ the variable reactances allow adjustment of the resonant frequency and the resistive component of the input impedance of the antenna at resonance
§ An input impedance at fc close to 50+j0 is achieved over the whole UHF-TV band without the use of inductors in the signal path, with plenty of bandwidth for an 8MHz DVB channel.
© Antenova 2009 Integrated Antenna and RF Solutions Commercial in Confidence
Gain: antennas for comparison
§ The output from the antenna on the PCB is connected near the mid-line of the PCB and is decoupled using a quarter-wave sleeve choke. DC lines are taped down, close to the ground-plane
§ The reference antenna is a coaxial dipole
§ The cables feeding both antennas were well decoupled.
Tuneable Antenna
Reference Antenna
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Test receiver
§ Test receiver was a DiBcom 9080M single-chip receiver This feeds the varactors via a voltage-doubler circuit
§ Test software was DiBcom’s Advanced Monitoring Tool, which was used to measure SNR, frame errors and signal spectra
§ Antennas were mounted in a clear outside environment, 1m above ground level
§ Local DVB-T transmitter is 34km (21 miles) from the test site, transmitting 15kW eirp on Channel 40 (626MHz) with horizontal polarisation. The C-OFDM transmitter is currently operating in 2k mode using 16-QAM.
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Signal spectrum: reference dipole
§ Reference dipole: Signal, Noise and SNR
40dB 30dB SNR 10dB 0dB
0dBm -20dBm Power -40dBm -60dBm
-4000 Frequency (kHz) 4000
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Signal spectrum: tuneable antenna
§ Planar tuneable antenna: Signal, Noise and SNR
40dB 30dB SNR 10dB 0dB
0dBm -20dBm Power -40dBm -60dBm
-4000 Frequency (kHz) 4000
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Demonstrations
HD ATSC programs in Santa Ana, California
Antenna on pcb lying in front of 11-in laptop Antenna pcb taped behind to lid of laptop
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An integrated Notebook antenna
This antenna is designed to provide tunable operation across the UHF band
This antenna fits within the lid, above the display panel, with the cables routed along one side
An additional insulated wire is used to provide a DC voltage to the tuneable matching circuit embedded within the antenna
Grounding is achieved by the use of a stick-down foil to the rear of the LCD housing.
DVB antenna Wireless internet
TV WiFi antenna
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Antenna concept development
RF input
5.002.001.000.500.200.00
5.00
-5.00
2.00
-2.00
1.00
-1.00
0.50
-0.50
0.20
-0.20
0.00 0
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708090100
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-120
-110-100 -90 -80
-70
-60
-50
-40
-30
-20
-10
Ansoft Corporation Narrow_Top_DesignInternal_DVB_Antenna
m1
m2
m3
Curve Info
S(LumpPort1,LumpPort1)Imported
S(LumpPort1,LumpPort1)DVB : Sw eep1
Name Freq Ang Mag RX
m1 0.4700 -142.3456 0.7797 0.1380 - 0.3351i
m2 0.6600 -123.0889 0.1546 0.8184 - 0.2172i
m3 0.8500 71.1492 0.7012 0.4894 + 1.2779i
400.00 450.00 500.00 550.00 600.00 650.00 700.00 750.00 800.00 850.00 900.00Freq [MHz]
-20.00
-18.00
-16.00
-14.00
-12.00
-10.00
-8.00
-6.00
-4.00
-2.00
0.00
dB(S
(Lum
pPor
t1,L
umpP
ort1
))
Ansoft Corporation Narrow_Top_DesignInternal_DVB_Antenna_Simulated_Return_Loss
m1
m2
m3
Curve Info
dB(S(LumpPort1,LumpPort1))DVB : Sw eep1
Name X Y
m1 470.0000 -2.1620
m2 670.0000 -19.7350
m3 850.0000 -3.0828
Impedance characteristic simulated using HFSS v11
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300 400 500 600 700 800 900 1000-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
∇ 1
∇ 2
∇
∇
[MHz]
[dB] mtool5
MARKERS: MHz dB
10000_vkn_Netbook_DVBAntenna21_2port Narrow_Top_Design.s2p1: 470 -2.162: 850 -3.08
MatchedData1: 470 -11.682: 850 -8.66
Tuneable matching circuit design
BBY57 series Varactor Diode Voltage/Capacitance curve
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35
0 0.5 1 1.5 2 2.5 3 3.5 4
Voltage (V)
Cap
acita
nce
(pF)
1MHz450-850MHz
Tuning Range
Simulated matching with varactor diode at 15pF capacitance
Data from HFSS
ZL
50
C22: 5.6 pF
10000_vkn_Netbook_DVBAntenna21_2port Narrow_Top_Design.s2p
C23: 15 pF
L24: 18 nH
L21: 10 nH
S21
Data from the HFSS model is used to develop the matching circuit, using interactive circuit simulation software.
The graph below shows how the capacitance of the varactor diode varies with the applied DC control voltage.
Parameters obtained from HFSS simulation
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Practical design of the matching circuit
DVB Antenna-Radome side
DVB Antenna-front/bezel side
0-2.6V DC in 18nH Varactor diode
100pF DC block
220nH RF block
To varactor diode
RF in
5.6pF 10nH
0-2.6V DC
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Antenna radiation efficiency
Tunable DVB Antenna2 - Proto X03/sim21 - Foil ground
0
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450 470 490 510 530 550 570 590 610 630 650 670 690 710 730 750 770 790 810 830 850 870
Frequency (MHz)
Rad
iatio
n Ef
ficie
ncy
(%)
0V 1.32V 1.81V 2.0V 2.4V 2.6V
Ch21 Ch24 Ch28 Ch34 Ch45 Ch56 Ch62 Ch66 Ch68
R
adia
tion
effic
ienc
y (%
)
0
10
20
30
4
0
50
60
450 500 550 600 650 700 750 800 850 Frequency (MHz)
Radiation efficiency measured in SATIMO S64 for different tuning voltages
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Mechanical details
Mechanical
Volume (Antenna body)
3.5cc
Width x Length x Height
4.0 mm x 10.2mm x 86mm
RF Feed
1.37mm OD miniature coaxial cable
Connection
Hirose U.FL connector
Webcam
Coax feed & tuning line
Tuneable UHF-TV antenna
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Gain at 500MHz
Polarisation Peak Gain YZ Peak Gain XY Peak Gain XZ
Theta θ -12.4 -5.8 -3.0 Phi φ -1.1 -1.1 -7.5 Total -0.8 -0.9 -2.9
Z
Y
X
Antenna
φ Plane
θ Plane
DC = 1.81V
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Z
Y
X
Antenna
Polarisation Peak Gain YZ Peak Gain XY Peak Gain XZ
Theta θ -7.6 -6.1 -1.8 Phi φ -1.2 -1.7 -6.3 Total -0.8 -0.7 -1.8 φ Plane
θ Plane
DC = 0V
Gain at 666MHz
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Z
Y
X
Antenna
Polarisation Peak Gain YZ Peak Gain XY Peak Gain XZ
Theta θ -6.9 -4.5 +0.3 Phi φ +0.3 -0.8 -7.2 Total +0.4 0.0 +0.4 φ Plane
θ Plane
DC = 2.0V
Gain at 800MHz
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An SMT Antenna
§ Small, tuneable UHF (470-862MHz) for handheld devices § Single tuning voltage 0-3.7V § Two varactors § High efficiency (>30%) § SMT (FR4 Module)
Size: 40x10x1.6mm
HFSS Model Actual prototype
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Results
§ Return loss and efficiency on a 120x40mm PCB
400 500 600 700 800 900 1000-25
-20
-15
-10
-5
0
5
∇ 1
∇ 2
∇ ∇∇
∇
[MHz]
[dB] mtool5
MARKERS: MHz dB
0V01: 470 -1.572: 870 -0.51
1V211: 470 -0.382: 870 -0.49
3V701: 470 -0.252: 870 -1.34
0
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470 520 570 620 670 720 770 820 870MHz
Effi
cien
cy [
%]
0V01V23V7ETSI Spec.
Work in progress: • Extend range at upper edge • Reduce max voltage <2.8V
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Conclusion
§ A tuned solution potentially has significant advantages for a small antenna which must cover a large frequency band
§ Over the UHF-TV band the advantage of continuous tuning relative to 3-bit step-tuning can be of the order of 4dB on a handset platform
§ Interactive tuning provides additional benefit and involves no significant extra cost
§ New technologies may out-perform the best varactor diodes, but they can’t do so at the present time
§ The most important design challenges for small tuned antennas for this application are the minimization of loss and the achievement of sufficient tuning range.
Note § The design of the double-tuned antennas described in this presentation is the subject of UK Patent
Application GB 0902307.8. § The authors are grateful to DiBcom SA for the loan of their DVB-T monitoring receiver and software
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References
Bibliography [1] L Huang and P Russer, Tunable Antenna Design Procedure and
Harmonics Suppression Methods of the Tunable DVB-H Antenna for Mobile Applications, EuMA, Munich 2007
[2] J Holopainen: Antenna for Handheld DVB Terminal, Master’s Thesis, Helsinki University of Technology, May 2005
[3] DVB-H Implementation Guidelines, DVB BlueBook A092, Digital Video Broadcasting Project, www.dvb.org
[4] Mobile and portable DVB-T/H radio access – Part 1: Interface specification, (EICTA MBRAI 2.0), www.eicta.org
[5] EBU Guidelines for the RRC-06, EBU I37-2006, European Broadcasting Union, Geneva 2006
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Thank you!
Thank you for your attention
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Stow-cum-Quy, Cambridge CB25 9AR, UK
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