13 EMLAB Advantage of a resonant circuit At resonance Generate higher voltage than input voltage. Maximum current level depends on internal resistance.
14 EMLAB How to generate time varying currents Electronic circuit generate oscillating voltages Output voltage Alternating currents accelerate electrons which emit electromagnetic waves propagating in perpendicular direction
16 EMLAB Radiation from an infinitesimally small current segment Exact solution :
17 EMLAB Far field approximation Electrostatic solution Biot-Savart’s law Coulomb’s law Near field approximation
18 EMLAB Radiation pattern of an infinitesimally small current
19 EMLAB Isotropic pattern Omnidirectional pattern Directional pattern Gain and directivity of an antenna : Gain takes into account losses and reflections of the antenna. Directivity 정의 : (Efficiency)
33 EMLAB N-element linear array antenna Uniform Array : Magnitudes of all currents are equal. Phases increase monotonically.
34 EMLAB Difference : Universal Pattern is symmetric about = Width of main lobe decrease with N Number of sidelobes = (N-2) Widths of sidelobes = (2π/N) Side lobe levels decrease with increasing N.
35 EMLAB Visible and invisible regions Array Factor 의 특성 Array factor has a period of 2 with respect to ψ. Of universal pattern, the range covered by a circle with radius “kd” become visible range. The rest region become invisible range 1 visible region Visible range of the linear array
36 EMLAB Grating Lobes Phenomenon If the visible range includes more than one peak levels of universal pattern, unwanted peaks are called grating lobes. To avoid grating lobes, the following condition should be met. 1 visible region grating lobes major lobe They have the same strength ! Example :, no grating lobe occurs
37 EMLAB 77GHz 에서 array element 들이 모두 동위상을 갖도록 설계함. 10mm 17mm 두께 0.127mm 비유전율 2.2 표면 전류 분포 Example : array antenna (77GHz)
41 EMLAB LPFA/D Digital Signal Processing (Amplitude & Phase) ~ Desired signal direction LPFA/D LPFA/D LPFA/D Interference or multipath signal direction Beamforming Approaches : Digital Beamformer (DBF)