tailieunhanh - Electromagnetic Waves and Antennas combined - Chapter 1

Maxwell’s Equations Đầu tiên là định luật cảm ứng Faraday, thứ hai là Amp `ere của pháp luật như sửa đổi, bổ sung một số điều của Maxwell bao gồm hiện tại chuyển ∂ D / ∂ t, thứ ba và thứ tư là pháp luật Gauss ' cho điện trường và từ trường. Thời hạn chuyển ∂ D / ∂ t trong pháp luật `ere của Amp là điều cần thiết trong việc dự đoán sự tồn tại của tuyên truyền sóng điện từ. | 1 Maxwell s Equations Maxwell s Equations Maxwell s equations describe all classical electromagnetic phenomena V XE St VxH J St V D p Maxwell s equations The first is Faraday s law of induction the second is Ampere s law as amended by Maxwell to include the displacement current SD St the third and fourth are Gauss laws for the electric and magnetic fields. The displacement current term SD St in Ampere s law is essential in predicting the existence of propagating electromagnetic waves. Its role in establishing charge conservation is discussed in Sec. . Eqs. are in SI units. The quantities E and H are the electric and magnetic field intensities and are measured in units of volt m and ampere m respectively. The quantities D and B are the electric and magnetic flux densities and are in units of coulomb m2 and weber m2 or tesla . D is also called the elecưic displacement and B the magnetic induction. The quantities p and J are the volume charge density and electric current density charge flux of any external charges that is not including any induced polarization charges and currents. They are measured in units of coulomb m3 and ampere m2 . The right-hand side of the fourth equation is zero because there are no magnetic mono-pole charges. Eqs. - display the induced polarization terms explicitly. The charge and current densities p J maybe thought of as the sources of the electromagnetic fields. For wave propagation problems these densities are localized in space for example they are restricted to flow on an antenna. The generated electric and magnetic fields are radiated away from these sources and can propagate to large distances to 2 1. Maxwell s Equations the receiving antennas. Away from the sources that is in source-free regions of space Maxwell s equations take the simpler form Vx at V XH at V D 0 V B 0 source-free Maxwell s equations The qualitative mechanism by which Maxwell s equations give rise to propagating .