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1 SCHOOL OF COMPUTER & COMMUNICATIONS ENGINEERING EKT 341/4 ANTENNAS AND PROPAGATION Lecturer: En. Rosmizi bin Abd Rahim Dr. Mohd Faizal Bin Jamlos PLV: Puan Hazila Othman

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2 Marks allocation: Final Exam : 50% Written Tests : 20% Mini Project : 10% Laboratory : 15% Quiz, Assignment & others : 5%

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3 Introduction Agilent Technologies offers a wide range of both scalar and vector network analyzers for characterizing components from DC to 110 GHz. These instruments are available with a wide range of options to simplify testing in both laboratory and production environments. Network Analyzer

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4 Types of Network Analyzer Scalar Magnitude only Broadband Detector with higher noise floor Lower Price Normalization – Less Accurate Measures RL, SWR, Gain/Loss Vector Phase and Magnitude Tuned Detector with lower noise floor Higher Price Complete Error Correction – More Accurate Measures all

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5 Network Analyzers Vs Spectrum Analyzers. Amplitude Ratio Frequency Amplitud e Frequency 8563A SPECTRUM ANALYZER 9 kHz - 26.5 GHz Measures known signal Measures unknown signals Network analyzers: l measure components, devices, circuits, sub-assemblies l contain source and receiver l display ratioed amplitude and phase (frequency or power sweeps) l offer advanced error correction Spectrum analyzers: l measure signal amplitude characteristics carrier level, sidebands, harmonics...) l can demodulate (& measure) complex signals l are receivers only (single channel) l can be used for scalar component test (no phase) with tracking gen. or ext. source(s)

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6 Why Use S-Parameters? l relatively easy to obtain at high frequencies n hard to measure total voltage & current at the device ports at high frequency n measure voltage traveling waves with a vector network analyzer n don't need shorts/opens which can cause active devices to oscillate or self-destruct l relate to familiar measurements (gain, loss, reflection coefficient...) l for RF design, S-parameters are easily imported and used for circuit simulations in electronic-design automation (EDA) tools like Agilent's Advanced Design System (ADS). S-parameters are the shared language between simulation and measurement.

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Vector Network Analyzer7 Measuring S-Parameters S 11 = Reflected Incident = b 1 a 1 a 2 = 0 S 21 = Transmitted Incident = b 2 a 1 a 2 = 0 S 22 = Reflected Incident = b 2 a 2 a 1 = 0 S 12 = Transmitted Incident = b 1 a 2 a 1 = 0 Transmitted S 21 S 11 Reflected b 1 a 1 b 2 Z 0 Load a 2 = 0 DUT Forward IncidentTransmitted S 12 S 22 Reflected b 2 a 2 b a 1 = 0 DUT Z 0 Load Reverse 1

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8 Basic Antenna Parameters

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Antenna Parameters 9 Radiation Pattern Input Impedance and Impedance Matching Return Loss / Reflection Coefficient ? Bandwidth VSWR Demo

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10 Radiation Pattern of generic directional antenna HPBW (3dB Beamwidth) : The half power beamwidth (HPBW) can be defined as the angle subtended by the half power points of the main lobe. Main Lobe: This is the radiation lobe containing the direction of maximum radiation. Minor Lobe: All the lobes other then the main lobe are called the minor lobes. These lobes represent the radiation in undesired directions. Back Lobe: This is the minor lobe diametrically opposite the main lobe. Side Lobes: These are the minor lobes adjacent to the main lobe and are separated by various nulls. Side lobes are generally the largest among the minor lobes. ***In most wireless systems, minor lobes are undesired. Hence a good antenna design should minimize the minor lobes. Antenna Parameters

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11 The input impedance of an antenna is defined as “the impedance presented by an antenna at its terminals or the ratio of the voltage to the current at the pair of terminals ”. An ideal antenna solution has an impedance of 50 ohm all the way from the transceiver to the antenna. Hence the impedance of the antenna can be written as: where Input Impedance Antenna Parameters

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12 Smith Chart Review Z = Z o L = 0 Constant X Constant R Smith chart L Z = 0 = ±180 O 1 (short) Z = L = 0 O 1 (open) Antenna Parameters

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13 The Return Loss (RL) is a parameter which indicates the amount of power that is “lost” to the load and does not return as a reflection. RL is a parameter similar to the VSWR to indicate how well the matching between the transmitter and antenna has taken place. The RL is given as : For perfect matching between the transmitter and the antenna, Γ = 0 and RL = ∞ which means no power would be reflected back, whereas a Γ = 1 has a RL = 0 dB, which implies that all incident power is reflected. Return Loss (RL)

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14 Return Loss (RL) Return Loss A very good antenna might have a value of -10dB (90 % absorbed & 10 % reflected).

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15 Bandwidth The range of frequencies on either side of the center frequency where the antenna characteristics like input impedance, radiation pattern, beamwidth, polarization, side lobe level or gain, are close to those values which have been obtained at the center frequency. The bandwidth of a broadband antenna can be defined as the ratio of the upper to lower frequencies of acceptable operation. The bandwidth of a narrowband antenna can be defined as the percentage of the frequency difference over the center frequency. The equations as follows: Antenna Parameters

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16 Bandwidth Bandwidth (BW) can be measured by looking at the frequency range where reflection coefficient value dropped below than -10 dB. Antenna Parameters

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17 VSWR VSWR is a measure of impedance mismatch between the transmitter and the antenna. The higher the VSWR, the greater the mismatch. The minimum VSWR, i.e., that which corresponds to a perfect impedance match, is unity. The result is presented as a figure describing the power absorption of the antenna. A value of 2.0:1 VSWR, which is equal to 90 % power absorption, is considered very good for a small antenna.

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Vector Network Analyzer18 Vertical Position Horizontal Position Half Wave Dipole Antenna

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hazila_2010 Radiation Pattern

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Vector Network Analyzer20 Radiation Pattern Yagi Antenna

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Vector Network Analyzer21 THE END

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