Analyzing the provided openEMS code for errors or issues

Okay, let's tackle this openEMS code correction. First, I'll go through the user's code step by step to identify possible issues
Starting with the simulation parameters. The frequency range is 2-4 GHz, which makes sense for through-wall applications. The mesh resolution is set to lambda/30, which should be fine, but maybe check if it's too coarse for the PBG structure
Looking at the FDTD setup, they're using PML boundaries on all sides. For antenna simulations, sometimes it's better to use MUR absorbing boundaries instead of PML, especially if the structure is radiating into free space. But PML might be okay here. The Gaussian excitation is centered at 3 GHz, which is correct
The substrate is FR4 with a thickness of 1.6 mm. The code adds a box for the substrate, but the dimensions are 100x100 mm. That seems a bit large. Maybe reduce it to save computation time, but ensure it's larger than the PBG and antenna structure
The biquad parameters: quad_len is lambda/4. Wait, lambda at 3 GHz is about 100 mm, so lambda/4 is 25 mm. That's a reasonable size. The wire radius is 1 mm, which is a bit thick for a printed antenna. Maybe the user intended a planar structure, so using a cylinder with radius might not be correct. Perhaps they should use a flat polygon with a certain width instead of a cylindrical wire
The rotation matrix function looks correct, converting angles to radians and combining rotations. The draw_biquad function creates a polygon for the biquad shape. However, the AddPolygon command uses 10 as the priority and 1 as the normal direction. Wait, in openEMS, the polygon priority might need to be higher than the substrate's to ensure it's on top. Also, the normal direction (1 in this case) should correspond to the plane; maybe that's okay
The ports are added as lumped ports between two points. The feed_offset is 0.5, but multiplied by unit (mm), so 0.5 mm gap. That's very small. Maybe the feed gap should be a fraction of the wavelength or based on the antenna design. Also, the ports are added in the z-direction, but the biquad is in the xy-plane, so maybe the port orientation is incorrect. Should it be in the x or y direction instead?
The PBG structure is made of metal cylinders arranged in a grid. The spacing is lambda/6, which at 3 GHz is about 16.6 mm. The loop skips the central 3x3 area where the antenna is. But the grid_range is from -3 to 3, which gives 7 elements in each direction. Wait, the loop uses 'if abs(ix) <=1 && abs(iy) <=1', which skips the center 3x3 (since ix and iy go from -3 to 3). That leaves a 5x5 grid around the antenna. But the PBG might need more periods for effective performance. Maybe increase the grid_range to cover more cells
The mesh definition uses SmoothMeshLines, but the mesh.x and mesh.y are set to [-lambda/2, 0, lambda/2], which creates a mesh around the center. However, the PBG structure extends beyond this range. The mesh should cover the entire PBG and antenna structure. So the current mesh might be too small, leading to parts of the structure being outside the mesh, causing errors
In the WriteOpenEMS and RunOpenEMS section, the code seems correct, but the user might have issues with the simulation directory permissions or OpenEMS not being properly installed
Post-processing: The calcPort function is called with f0, but it's better to calculate over the frequency sweep. The S11 plot uses port{1}.S11, but if the simulation didn't run correctly, this would fail. Also, the ports might not be correctly defined, leading to incorrect S-parameters
Possible fixes:
  1. Replace the cylindrical biquad elements with planar polygons of appropriate width
  2. Adjust the mesh to cover the entire PBG and antenna structure
  3. Correct the port orientation and feed gap size
  1. Ensure the substrate size is adequate but not excessively large
  2. Verify the PBG structure's periodicity and number of elements
  3. Check boundary conditions, maybe switch to MUR for antenna simulations
  1. Use a correct frequency range in calcPort for S11 calculation over the sweep
    Implementing these changes should make the code workable

Comments

Post a Comment

Popular posts from this blog

Procedure for Microwave Simulation lab MSc 4th Sem 2025

Experiment A  Step 1 :  Run the python code https://openemsres.blogspot.com/2025/04/a-patch-antenna-design-bounded-by-sine.html . Keep modifying the values of  the parameters m, n , p and q to until a  nicer design is obtained. Step2 : Visually verify the design and then open the generated text file  Step3:  find and replace all (Ctrl+H)  x_coordinate with 1 and y_coordinate with 2 . Save the file  Step4 Copy the code in  https://openemsres.blogspot.com/2025/04/openems-code-to-generate-and-simulate.html Step5 : Find   % Define the custom patch using AddCurve  and  Replace all the  the points below that with the new coordinates generated in step 3 Step6.  Create a folder "YourRollNoEMS_ExA" in C:\openEMS\matlab and  Save the file in step 5 as patchDesign_YourRollNo.m inside that folder.  Step7. Start Octave and change the  work directory to the folder created in step 6. Wait and  Click the onsc...
Read more

A patch antenna design bounded by sine curves

import numpy as np import matplotlib.pyplot as plt # Patch dimensions patch_width = 32 patch_length = 40 # Parameters N = 800               # Total number of points amplitude = 2.5       # Sinusoidal amplitude wavelength = 20       # Wavelength of sinusoidal modulation # Rectangle outline as a single parametric path def generate_wavy_rectangle(w, l, N, amp, wave_len):     # Perimeter breakdown     total_perim = 2 * (w + l)          # Linear distance around perimeter     t = np.linspace(0, total_perim, N)          x = np.zeros_like(t)     y = np.zeros_like(t)     # Segment positions     bottom = t <= w     right = (t > w) & (t <= w + l)     top = (t > w + l) & (t <= 2*w + l)     left = t > 2*w + l     # Parametric path     x[b...
Read more

Filter design using fractral geometry (Sierpinski resonator with a microstrip feed)

% Clear and initialize close all; clc; % Add OpenEMS and CSXCAD paths addpath('C:\openEMS\matlab'); addpath('C:\openEMS\CSXCAD\matlab'); % Constants c0 = 299792458;  % Speed of light in vacuum [m/s] unit = 1e-3;     % millimeter %% Adjustable Parameters iter = 2;                    % Sierpinski depth sideLength = 30;            % Triangle side [mm] substrate_thickness = 1.6;  % mm eps_r = 4.4;                % Dielectric constant of FR4 f_start = 1e9;              % Simulation start frequency f_stop = 10e9;              % Simulation stop frequency res = 30;                   % Mesh resolution factor %% Calculate microstrip width for 50 Ohm Z0 = 50; h = substrate_thickness; er = eps_r; if Z0 <= 60     W = (8 * h) *...
Read more