ICE5108084 Antenna Design Lecture 4 Antenna Pattern Paramters

4. 1 Antenna Pattern Parameters § Pattern parameters: - Main lobe (주엽), sidelobes (부역),

§ Main lobe: - Main beam maximum = Maximum gain Antenna boresight - Main

§ Sidelobe and backlobes: - Local maximum radiation off the antenna main beam -

§ Sidelobe and backlobes: - The smaller the sidelobes, the larger the beamwidth and

- SLL (sidelobe level): The largest sidelobe level relative to the main lobe Uniform

§ Beamwidth (BW): - Antenna beamwidth = Half-power beamwidth (HPBW) = BW = θ

§ Null: - Very small radiation or reception in null direction - Adaptive nulling:

§ CRPA Block Diagram: - Adaptive beamforming - Smart antenna - Implementation in SDR

§ Antenna parameters vs. current distribution: - Line source: Current flows on a wire.

§ Antenna pattern rule of thumb: 3 d. B = ( /L) × 75°

4. 2 Short Dipole Antenna § Ideal dipole antenna: - Dipole length << Wavelength

§ Radiation resistance and efficiency: 14

ICE-5108084 Antenna Design Lecture 4: Antenna Pattern Parameters 18

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ICE-5108084 Antenna Design Lecture 4: Antenna Pattern Paramters 4. 1 Antenna Pattern Parameters 4. 2 Short Dipole Antenna 1

4. 1 Antenna Pattern Parameters § Pattern parameters: - Main lobe (주엽), sidelobes (부역), back lobes (후엽) - HPBW (half-power beamwidth) (반치각, 빔폭): 최대방사의 1/2이 되는 각도범위 - Null (영점) - 10 -d. B BW (10 d. B 빔폭) - BWBN (beamwidth between nulls) (영점각) Figure: Antenna pattern parameters 2

§ Main lobe: - Main beam maximum = Maximum gain Antenna boresight - Main beam electronically scanned Phased array antenna - Multibeam antenna: Many main beams at the same time 3

§ Sidelobe and backlobes: - Local maximum radiation off the antenna main beam - The first sidelobe: Largest - Interferences in communication, false targets in radars RPE (radiation pattern envelope) specifications 4

§ Sidelobe and backlobes: - The smaller the sidelobes, the larger the beamwidth and the smaller the directivity - Useful sidelobe levels: 30 to 20 d. B: Communications, radar 50 to 30 d. B: Low sidelobe military radars - Back lobe: Around θ = 180° - Front-to-back ratio (F/B): Main lobe maximum (d. B) Back lobe maximum (d. B) 5

- SLL (sidelobe level): The largest sidelobe level relative to the main lobe Uniform line source : 13. 3 d. B Tapered line source : 50 to 20 d. B - Radiation pattern due to uniform current Normanized pattern of a uniform line source (2 a : line source length) 6

§ Beamwidth (BW): - Antenna beamwidth = Half-power beamwidth (HPBW) = BW = θ 3 d. B - Radar's angular resolution - Smaller the beamwidth, the higher the directivity and the longer or larger the antenna - The smaller the sidelobes, the larger the beamwidth Optimum current distribution for the smallest beamwidth for a specified sidelobe level - Sum of power radiated = Power radiated in HPBW with max. gain 7

§ Null: - Very small radiation or reception in null direction - Adaptive nulling: Interference or jamming suppression - Anti-jam GPS antenna - CRPA (controlled reception pattern antenna) 8

§ CRPA Block Diagram: - Adaptive beamforming - Smart antenna - Implementation in SDR (software defined radio) 9

§ Antenna parameters vs. current distribution: - Line source: Current flows on a wire. 10

§ Antenna pattern rule of thumb: 3 d. B = ( /L) × 75° null = 2. 5 3 d. B D = 1. 5 L / (linear antenna) D = 2 D (linear antenna with ground plane) D = 8 (A / λ 2) (planar antenna) SLL = 25 d. B (sidelobe level) - Directivity from beamwidth D = 120 / 3 d. B(deg. ) (linear antenna) D = 25000 /[ 3 d. B, E(deg. ) 3 d. B, H(deg. )] (planar antenna) 11

4. 2 Short Dipole Antenna § Ideal dipole antenna: - Dipole length << Wavelength - Current distribution I (z) = IA = I 0 (uniform; theoretical model) - Use the spherical coordinate system 12

§ Antenna directivity calculation: 13

§ Radiation resistance and efficiency: 14