tailieunhanh - Microwave Ring Circuits and Related Structures phần 4

Hình minh họa một yếu tố hình khuyên vòng kết hợp với một khu vực 45 ° cao trở kháng cộng hưởng địa phương (LRS). Theo phân tích mô hình sóng đứng, chỉ có Bốn loại các chế độ chia: (a) cùng chia chế độ, (b) phân chia cộng hưởng chế độ địa phương, (c) notch nhiễu loạn phân chia chế độ; (d) bản vá nhiễu loạn phân chia chế độ. | 102 ELECTRONICALLY TUNABLE RING RESONATORS FIGURE Diagram of a varactor package cross section. FIGURE Equivalent circuit of a packaged varactor. equivalent circuit given in Figure can also be used for diodes other than varactors. The only difference will be the value of the parameters. In Figure Cj is obviously the capacitance that arises from the semiconductor junction. It is this value in which we are most interested all the others are undesirable but unavoidable. The value Rs is the series resistance due primarily to the bulk resistance of the semiconductor. Minimizing Rs increases the Q of the varactor here Q 1 wRjCy reducing power losses in the circuit and increasing the overall circuit Q. Typically higher Q-values are obtainable with hyperabrupt junction varactors because of the lower bulk resistance. The parameters Cp Lp and Ls are the parasitics introduced by the package. The capacitance Cp which appears in shunt is a combination of the capacitance that exists between the upper contact and the metallic mount of the semiconductor and the insulating housing. Because of the close spacing required in microwave frequency circuits particularly for small elements that INPUT IMPEDANCE AND FREQUENCY RESPONSE 103 possess small junction capacitances the capacitance contribution can become quite significant. The capacitance C2 is also included in Figure . Here C2 is the capacitance that arises from the gap in the transmission line across which the diode will be mounted. This is the same gap capacitance discussed in Chapter 2. The gap shunt capacitance C1 is omitted because its effects are considered to be negligible. In addition to the capacitances all metallic portions of the package will introduce inductance. The inductance is divided into two components Ls and L .The inductance Lp appears in series with the junction most significant contributions of the inductance come from the metallic contacting strap and the post .