Frequency Independent Antenna • Log Periodic Antennas 0 1 2 1 2 Self- complementary: When metal is replaced by air and vice versa, the resultant antenna is identical to the original one =45 ° = 135 ° Teeth width and gap equalized: = = + 1 = √
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Frequency Independent Antenna Log Periodic Antennas Self-complementary: When metal is replaced by air and vice versa, the resultant antenna is identical.
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Frequency Independent Antenna • Log Periodic Antennas
𝑅
𝑟0
𝛼𝛽
𝑅1
𝑅2
𝑎1𝑎2
Self-complementary:When metal is replaced by air and vice versa, the resultant antenna is identical to the original one 𝛽=45 °
𝛼=135 °Teeth width and gap equalized:
𝜎=𝑎𝑛
𝑅𝑛
=𝑅𝑛+1
𝑎𝑛
=√𝜏
Frequency Independent Antenna • Log Periodic Antennas
Frequency Independent Antenna • Log Periodic Dipole Array (N elements)
𝛼 𝐿1
𝑅𝑛+1
𝑅𝑛
𝑑𝑛
𝜏=𝑅𝑛+1
𝑅𝑛
=𝐿𝑛+1
𝐿𝑛
<1
𝜎=𝑑𝑛
2𝐿𝑛
𝐿1
𝑅1
=𝐿2
𝑅2
=…=𝐿𝑁
𝑅𝑁
𝑑𝑛=𝑅𝑛−𝑅𝑛+1
¿ (1−𝜏)𝑅𝑛
tan𝛼2
=𝐿𝑛
2𝑅𝑛
𝜎=1−𝜏
4 tan𝛼2
𝐿1≈𝜆𝐿
2𝐿𝑁 ≈
𝜆𝑈
2
Frequency Independent Antenna • Log Periodic Dipole Array (N elements)
𝛼 𝐿1
𝑅𝑛+1
𝑅𝑛
𝑑𝑛
Frequency Independent Antenna • Log Periodic Dipole Array (LPDA)
Gain contour
Frequency Independent Antenna • LPDA Design Example
Gain contour𝑓 =54 216 MHz
Gain
𝜏=0.822𝜎=0.149
𝐿1=λ𝐿2
=5.562
=2.78m
𝐿𝑁=λ𝑈2
=1.3892
=0.694m
Frequency Independent Antenna • LPDA Design Example
𝑓 =54 216 MHzGain
𝜏=0.822𝜎=0.149
𝐿1=2.78 m
2.78 0.828
2.29 0.682
1.88 0.560
1.54 0.459
1.27 0.378
1.04 0.310
0.858 0.256
0.705 0.210
0.579 N/A𝑑𝑛=2𝜎 𝐿𝑛=0.298𝐿𝑛
𝐿𝑁=0.694 m
Frequency Independent Antenna • LPDA Design Example II
𝑓 =200 600 MHzGain
𝜏=0.917𝜎=0.169
𝐿1=λ𝐿2
=1.52
=0.75 m
𝐿𝑁=λ𝑈2
=0.52
=0.25 m
Frequency Independent Antenna • LPDA Example II
Voltages
Frequency Independent Antenna • LPDA Example II
Currents
Frequency Independent Antenna • LPDA Example II: Patterns
Frequency Independent Antenna • LPDA feed schemes
Frequency Independent Antenna • LPDA feed schemes
Yagi-Uda Antenna• Antenna with parasitic elements
~
Driven element
Reflector Directors
Yagi-Uda Antenna
Yagi-Uda Antenna
Yagi-Uda Antenna• Computer program (Prof. Balanis)
• N = 15• Number of directors = 13• Number of reflectors = 1• Length of reflector = 0.5 • Length of driven element = 0.47 • Length of directors = 0.406 • Spacing between reflector and driven element = 0.25 • Spacing between directors = 0.34 • Radius of wires = 0.003
Yagi-Uda Antenna• Computer program (Prof. Balanis)