31 Radiation Pattern 32 Spherical Coordinate System 33 Antenna Field Regions 34 Antenna Efficiency 35 Directivity and Gain 31 Radiation Pattern 2 Radiation pattern 방사패턴 ID: 1031486
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1. 1Antenna EngineeringLecture 3: Antenna Gain3.1 Radiation Pattern3.2 Spherical Coordinate System3.3 Antenna Field Regions3.4 Antenna Efficiency3.5 Directivity and Gain
2. 3.1 Radiation Pattern2Radiation pattern (방사패턴): - Electric field vs. angle - Linear scale: F(, ) = | E(, ) | = | E(, ) a + E(, ) a | - Log scale: F(, ) (dB) = 20 log10 | E(, ) |3D pattern (3차원 패턴): 전체적인 방사패턴 확인에 적합 - Normalized (정규화된) pattern: 최대값을 0dB로 하여 도시 - Unnormalized pattern: 이득값을 그대로 도시 3D patterns of a dipole antenna (left) and of a helical antenna (right)
3. 3Normalized and unnormalized patterns comparison: Normalized pattern (left) and unnormalized pattern (right)
4. 42D patten: 평면 컬러 plot. 방위각과 고각 방향의 전기장 변화 동시 확인 Cartesian (= Rectangular) pattern: 직각좌표 plot. 방위각 또는 고각방향 전기장 변화 도시 - Antenna boresight: Direction of the maximum gain - Antenna surface (or aperture) normal: 안테나 면에 수직인 방향 - Antenna boresight ≠ Surface normal: Scanned beam28-GHz base station antenna for 5G mobile communication (left), 2D pattern (center) and Cartesian pattern (right)
5. 5Polar plot: - 극좌표 plot - 방위각 또는 고각방향 전기장 변화 도시 - Useful for broad pattern Yagi antenna (left), polar pattern (center) and 3D pattern (right). x axis = boom direcon, y axis = dipoledirection
6. 6Polar plot vs Cartesian plot: - Polar plot: 각도에 따른 방사세기를 직관적으로 확인 편리 - Cartesian plot: 패턴 각도를 정확하게 확인 편리. 빔폭이 작은 안테나에 흔히 적용 Polar (left) and rectangular (right) patterns of a same antenna
7. 7Antenna radiation patterns: - Directivity (지향도) pattern - Gain (이득) pattern - Axial ratio (축비) pattern Directivity (left), gain (center), and axial ratio (right) patterns
8. 3.2 Spherical Coordinate System8Spherical coordinates (구좌표): - Coordinates: r : Distance from the origin : Angle from the positive z axis. Elevation angle = 90° φ : Angle from the positive x axis in the CCW direction around the positive z axis. Azimuth angle - Unit (or base) vectors: Spherical coordinate sysem
9. 9Radiation pattern in spherical coordinate system: - Any antenna's far field has only theta and phi components. Er = 0 - For any antenna, the following expression expression holds at the far-field region. - Magnetic field is related to the electric field through the intrinsic impedance.Figure: E-field, H-field, and wave direction
10. 103D radiation pattern in spherical coordinate: - Useful for study of overall pattern behavior Pyramidal horn antenna and its 3D radiation pattern
11. 3.3 Antenna Field Regions11Antenna field regions (안테나 전자기장 영역): - Near field region (근거리 영역): Electric and magnetic stored energy (or reactive field) dominant. Capacitive coupling and inductive coupling between antennas - Fresnel (프레넬) region (방사성 근거리 영역): Reactive and radiative fields present Electromagnectic (EM) coupling and radiative coupling - Far field region (원거리 영역): Radiative field dominant. Radiative coupling Antenna directivity and gain specified at far-field distance. Antenna pattern independent of distance from the antenna. Antenna field regions (left) and their boundary (right) (D = antenna size, λ = wavelength)
12. 12Small-antenna (소형 안테나) field regions: - For small antennas with size less than half wavelength: D < 0.5λField regions of antennas with size less than 0.5 λ
13. 13Antenna field regions vs. applications: - Far-field region: Communication, radar - Near-field region: Wireless charging, NFC - Fresnel region: UHF RFID, CATR (compact antenna test range) E-field to H-field ratio vs distance from an antenna
14. 14Antennas operating in far-field region: GPS Block III satellite - 2018 2023: Ten satellites - Civillian signal 1-3 m accuracy (now 3-10 m) - Military M-code harder to jam GPS Block III satellete in space (left) and in test laboratory (right)
15. 15Antennas operationg in Fresnel region: - CATR (compact antenna test range) Compact antenna test range: photo (upper right), floor plan (lower left), field uniformity in the test zone (lower right)
16. 16Antennas operationg in near-field region: - Inductive wireless charging of batteries Near-field coupled coils (left) and their magnetic field (right) in inductive charging - NFC reader and card/smartphone Near-field coupling in NFC card system (left) and Arduino kit (right)
17. 3.4 Antenna Efficiency17Antenna efficiency: - Radiated power to input power ratio Pr = ePi (Pi : input power, e : efficiency, Pr : radiated power)For high efficiency, - Reduce loss: Use low-loss dielectric material (tan = 0.002) - Achieve impedance matching: Small reflection coefficient (Zin Z0) Small antenna: Radius R enclosing the antenna (upper left), small antenna gain lmit (lower left), and small antenna gain vs. length (right)
18. 18Antenna efficiency derivatioin: Pr = ePi Pi = PA + PB (input power) PB = | Г |2Pi (reflected power) PA = PL + Pr = (1 | Г |2) Pi (power delivered to antenna) Pr = ePi = (Pr / PA ) (PA / Pi ) Pi e = Pr / Pi = er em (antenna efficiency, total efficiency) er = Pr / PA = Pr / (PL + Pr) = Rr / (RL + Rr) (radiation efficiency) em = PA / Pi = 1 | Г |2 (impedance matching efficiency) Pi : input power, PA : power delivered to antenna PL : loss power (conductor loss + dielectric loss) (손실전력) Pr : radiated power (방사전력), PB : reflected power (반사전력) RL : loss resistance (손실저항), Rr : radiation resistance (방사저항) Antenna power relationAntenna equivalent circuit
19. 3.5 Directivity and Gain19Antenna directivity (지향도): - Directivity: Directional radiation property - Power density relative to isotropic (등방성) antenna - D(, ): Directivity pattern - D = max [D(, )]: (Maximum) directivity D (dB) = 10log10D D = 4π (Ae/λ2) (directivity) Ae = 0.5 Ap 1.0 Ap (antenna effective area)Directivity of common antennas - Short dipole: 1.5 = 1.8 dBi (dB relative to isotropic radiator) - Half-wave dipole: 1.64 = 2.2 dBi - Patch antenna: 5 7 dBi - Yagi antenna: 3 20 dBi - Helical antenna: 5 16 dBi - Reflector antenna: 10 80 dBi - Array antenna: 5 40 dBi Directivity and gain
20. 20Antenna directivity pattern: - Example: A half-wave dipole. 3D and polar directivity patterns. Half-wave dipole (upper left), its directivity pattern in 3D (upper right), directivity pattern in azimuth plane (lower left), and directivity pattern in elevation plane (lower right)
21. 21Antenna directivity units: - Isotropic (등방성) 안테나: D = 0 dB Isotropic antenna: Theoretical concept. Phyiscally impossible to realize. - dBi : Directivity relative to the isotropic antenna directivity - dBd : Directivity relative to the half-wave dipole directivity dBd = dBi + 2.15 - dBc : Directivity relative to the circularly polarized isotropic antenna
22. 22Directivity arithmetic:Directivity with number of dipoles (left) and directivity of dipoles on a reflector (right)
23. 23Antenna gain: - Gain from directivity: G = eD G : antenna gain e : antenna efficiency D : antenna directivity G (dB) = 10log10 GAntenna gain components: - Gtheta = G : Corresponds to E at the far field - Gphi = G : Corresponds to E at the far field - Gabs : Corresponds to [(E)2 + (E)2]1/2
24. 24Gain pattern cut-plane: - Horizontal plane: Azimuth (방위각) plane - Vertical plane: Elevation plane - E-plane (전계면): Plane parallel to E vector - H-plane (자계면): Plane parellel to H vector - E vector and electric current vector are on the same plane. E-plane and H-plane of a vertical dipole
25. 25Antenna gain pattern example: - Sarantel GeoHelix - P2 embedded passive GPS antenna: Pt. no. 1010046 - QHA (quadrifilar helix antenna) Sarantel GeoHelix antenna (left), structure (center), and gain pattern (right)