Điện cảm Đối với thiết kế ăng-ten tag với một vi mạch trước khi lựa chọn với một điện dung nội bộ Cr, nhiệm vụ là để cấu hình một cuộn dây ăng-ten cộng hưởng ở tần số hoạt động. Nếu Cp được biết đến (so với Cr, Cp thường rất nhỏ trong dải tần HF, C ≈ Cr, độ tự cảm cần thiết của các ăng-ten cuộn dây là L = 1 2 f 2C () | 44 Handset Antennas of a calibrated standard-gain antenna - usually a horn or a standard dipole. Great care must be taken in the design of cables and connections within the measurement system and careful attention paid to mechanical stability and the protection of vulnerable components from damage. The effects of temperature change on system calibration must be assessed they may be reduced by careful system design or by limiting the extent to which the ambient temperature is able to vary. Efficiency Efficiency is measured by integrating the total power flux or gain measured over the whole spherical surface containing the device under test. The details of computation vary according to the distribution of the measurement points over the virtual measurement surface. Specific Absorption Rate SAR is measured by placing the handset under test next to a plastic phantom head filled with a sugar-saline solution with similar dielectric properties to brain tissue. A probe is moved inside the phantom and field levels are measured as its position is varied. Industrialgrade robotic control is used in high-accuracy systems capable of absolute measurements for certification purposes while comparative tests can be made with less costly hand-operated equipment. Hearing Aid Compatibility This is evaluated by measuring the axial and radial magnetic fields in the vicinity of the user s ear 21 . Design Optimization This begins with the adjustment of the antenna and matching circuit to achieve a low input VSWR over the working bands followed by measurement of the efficiency of the antenna in place on the handset. Efficiency is usually optimized by investigating and modifying the interactions between the antenna and other handset components and by reference to simulations to assist with an understanding of the fields and loss processes which may be occurring. Optimization is not easily reducible to a simple procedural algorithm. It requires clear .
