RF MODULE

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Thermal Drift in a Microwave Filter Introduction Microwave filters serve to suppress unwanted frequencies in the output of microwave transmitters. Amplifiers are in general nonlinear and produce harmonics that must be suppressed using one or several narrow passband filters on the output. High frequency stability of such filters can be hard to achieve because microwave systems may be subject to thermal drift caused by high-power loads or harsh environmental conditions like exposure to direct sunlight in the desert. Thus, system engineers need to estimate the drift of the passband frequency that arises due to thermal expansion of a filter. Model Definition Figure 3-10 shows the filter geometry. It consists of a box with a cylindrical post centered on one face. It is typically made of brass covered with a thin layer of silver to minimize losses. The silver layer is sufficiently thin to have a negligible influence on the device’s thermal and mechanical properties. Figure 3-10: A microwave filter consists of a box-shaped thin metallic shell, typically made of brass, that contains a cylindrical post. This configuration forms a closed air-filled electromagnetic cavity between the box walls and the post. The thermal expansion and the associated drift in eigenfrequency are caused by a uniform increase of the temperature of the cavity walls. The thermal expansion is readily computed using the Shell application mode from the Structural Mechanics 96 | CHAPTER 3: <strong>RF</strong> AND MICROWAVE MODELS
Module. The electromagnetic cavity mode analysis is easily performed using the 3D Electromagnetic Waves application mode in the <strong>RF</strong> Module. In principle, it is possible to determine the thermal drift in the passband frequency by repeated calculation of the thermal expansion followed by an electromagnetic mode analysis of the deformed geometry. A complication arises, however, because it is not wise to regenerate the mesh—doing so would introduce too much numerical noise. A better approach is to use a special set of equations to smoothly deform the original mesh according to the thermal expansion. Thus, the model uses the Moving Mesh (ALE) application mode for deformed geometry in COMSOL Multiphysics to map the thermal expansion to the geometry used for the electromagnetic analysis. Results and Discussion MODELING THE THERMAL EXPANSION The filter’s temperature can rise due to power dissipation in the filter itself, in the surrounding electronics, or due to external heating. Figure 3-11 shows the thermal expansion results for a filter entirely made of brass. Figure 3-11: Thermal expansion at 100 °C above the reference temperature. THERMAL DRIFT IN A MICROWAVE FILTER | 97
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COMSOL Multiphysics RF MODULE V ERS
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CONTENTS Chapter 1: Introduction Mo
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Results and Discussion. . . . . . .
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Chapter 4: Optics and Photonics Mod
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1 Introduction The RF Module Model
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highlights. The categories here inc
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TABLE 1-1: RF MODULE MODEL LIBRARY
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2 Tutorial Models This chapter cont
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Results and Discussion Figure 2-1 s
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4 Draw a square with corners at (
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COMPUTING THE SOLUTION Click the So
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Results and Discussion The dipole a
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PHYSICS SETTINGS Variables 1 Choose
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5 Click OK to close the dialog box
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Model Library path: RF_Module/Tutor
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4 From the Solve menu, open the Sol
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them from the eigenvalues. The appl
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5 On the Port page, set the values
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5 On the Port page, enter 36.4 in t
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Waveguide Optimization Introduction
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Results and Discussion Figure 2-3 s
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Modeling Using the Graphical User I
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3 Select Boundary 7 and set the Con
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POSTPROCESSING AND VISUALIZATION Fo
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The solution takes a few minutes to
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Night side Earth surface Ionosphere
Page 53 and 54: Results and Discussion The model pr
Page 55 and 56: 4 Select both spheres and click the
Page 57 and 58: RF and Microwave Models In this cha
Page 59 and 60: measure of the transmittance and re
Page 61 and 62: y 1 cm is at about 7.5 GHz. At the
Page 63 and 64: By feeding the circulator at a diff
Page 65 and 66: Importing the Geometry from a Binar
Page 67 and 68: MESH GENERATION This model uses the
Page 69 and 70: It is more instructive to look at t
Page 71 and 72: Note: When displaying S-Parameter v
Page 73 and 74: Monoconical RF Antenna Introduction
Page 75 and 76: 50 Ω, to obtain maximum transmiss
Page 77 and 78: Figure 3-7 shows the antenna radiat
Page 79 and 80: 2 Select the RF Module>Electromagne
Page 81 and 82: 13 Zoom in around (0, 0) using the
Page 83 and 84: 4 In the Contour levels area, click
Page 85 and 86: 2 Clear the Keep current plot check
Page 87 and 88: 6 Click the Solve button on the Mai
Page 89 and 90: Results and Discussion The figure b
Page 91 and 92: PHYSICS SETTINGS Point Settings Def
Page 93 and 94: 2 In the x-axis area, select the Ex
Page 95 and 96: Because the impedance is inversely
Page 97 and 98: 4 From the Space dimension list, se
Page 99 and 100: 2 Select Boundaries 1, 2, 4, and 6.
Page 101 and 102: 4 On the Pointwise Constraints page
Page 103: 12 Click the Solve button on the Ma
Page 107 and 108: EIGENFREQUENCY VS. TEMPERATURE By r
Page 109 and 110: GEOMETRY MODELING 1 Go to the Draw
Page 111 and 112: 3 Set dx, dy, and dz to u, v, and w
Page 113 and 114: 20 Select the Solve using solver se
Page 115 and 116: Computing the Solution Using a Para
Page 117 and 118: 8 Click Solve. 9 When the parametri
Page 119 and 120: H-Bend Waveguide with S-parameters
Page 121 and 122: Model Library path: RF_Module/RF_an
Page 123 and 124: 1 From the Postprocessing menu, cho
Page 125 and 126: The rectangular port is excited by
Page 127 and 128: Figure 3-16 shows a single-mode wav
Page 129 and 130: Figure 3-18: The S 21 parameter (in
Page 131 and 132: PHYSICS SETTINGS First set up the b
Page 133 and 134: FREEZING THE BOUNDARY MODE ANALYSIS
Page 135 and 136: 12 Click the Solve button on the Ma
Page 137 and 138: Microwave Cancer Therapy Introducti
Page 139 and 140: The model takes advantage of the pr
Page 141 and 142: DOMAIN AND BOUNDARY EQUATIONS—HEA
Page 143 and 144: Figure 3-23: The computed microwave
Page 145 and 146: solutions for both the electromagne
Page 147 and 148: 4 Select Subdomain 1, then enter th
Page 149 and 150: 1 Click the Plot Parameters button
Page 151 and 152: sar_in_human_head_interp.txt. That
Page 153 and 154: The bioheat equation produces a sim
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3 Click OK. 4 From the Options menu
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17 In the Work-Plane Settings dialo
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SETTINGS SUBDOMAIN 19 epsilonr_brai
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4 Click the Init tab and type 0 in
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POSTPROCESSING AND VISUALIZATION 1
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The walls of the oven and the waveg
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Figure 3-29: Temperature in the cen
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3 Click the block symbol again and
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2 At the waveguide end, Boundary 23
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4 Click OK to generate the plot bel
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Because the filter cutoff should be
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the force is applied. Figure 3-32 d
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6 Then the ECAD Import Options dial
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PHYSICS SETTINGS Subdomain Settings
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solver takes more steps than it sto
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3 Select Subdomain 1 and clear the
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13 Click the Solve button on the Ma
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Balanced Patch Antenna for 6 GHz In
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k0 = ω ε0 µ 0 All metallic objec
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divided by the input power. In Figu
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Reference 1. E. Recht and S. Shiran
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10 Select the objects SQ2, CO1, and
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43 Specify two spheres with the fol
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inputs are feeding the antenna, lik
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the width of the PML is equal to λ
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a toggle button that shifts between
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5 Select Coarse solver from the tre
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maxE = max(EdB); minE = min(EdB); E
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exterior of the PML that shows a ve
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13 Choose Extrude from the Draw men
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2 Click the Settings button. 3 In t
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Sea Bed Logging Introduction The Se
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Figure 3-39: Electric field magnitu
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PHYSICS SETTINGS Scalar Variables 1
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5 Click the General tab. From the P
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Optics and Photonics Models In this
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Model Definition The model is built
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Model Library path: RF_Module/Optic
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PHYSICS SETTINGS Scalar Variables S
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POSTPROCESSING AND VISUALIZATION By
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Model Definition The geometry is a
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2 In the list of application modes,
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Because the refractive index of GaA
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5 Click OK twice to see the followi
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Bandgap Analysis of a Photonic Crys
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a 2 a 3 × b1 = 2π----------------
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The five lowest bands for the (1, 1
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Modeling Using the Graphical User I
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Subdomain Settings 1 Open the Subdo
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3 Click the Parametric tab. Select
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3 Click OK to see the following plo
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fem.appl{1}.prop.analysis = 'harmon
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Model Definition The mode analysis
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2 Select the RF Module>Perpendicula
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4 On the Contour page, give Magneti
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includes only two independent param
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OPTIONS AND SETTINGS 1 Open the Con
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The problem becomes well-posed by a
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POSTPROCESSING AND VISUALIZATION Th
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7 Click OK. 8 From the Postprocessi
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the computed propagation constants
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3 The default eigenmode is the one
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Compare these ideal values of the p
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Stress-Optical Effects with General
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The PDE solved is Navier’s equati
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and εx ∂u = ∂x εy ∂v = ∂y
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Model Library path: RF_Module/Optic
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NAME EXPRESSION DESCRIPTION B2 0.65
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2 In the Subdomain Expressions dial
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4 Initialize the mesh in this geome
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Note: This model includes an extens
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3 Enter 1.46 in the text field Sear
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In these expressions, w 0 is the mi
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After 90 fs the pulse has reached t
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4 Select the RF Module>In-Plane Wav
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Boundary Conditions 1 From the Phys
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6 Click the Remesh button; when the
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2 On the General page, make sure th
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Propagation of a 3D Gaussian Beam L
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Figure 4-15: After 20 fs the pulse
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7 Click the Delete Interior Boundar
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Boundary Conditions 1 From the Phys
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5 From the Options menu, select Sup
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INDEX 3D electromagnetic waves mode
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efractive index 222, 254 resistance
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RF MODULE

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