# CST – Computer Simulation Technology

## Antenna Placement on a Box

This article serves to demonstrate the accuracy of the Integral Equation Solver in CST MICROWAVE STUDIO® (CST MWS) which is used to calculate the input impedance of a monopole antenna on a conducting box. The geometry and results are taken from [1]. Figure 1 shows the geometry of the structure and the discrete face port excitation. A monopole antenna with a length of 6 cm is mounted on a cubic box with a side length of 10 cm. The box is placed on an infinite ground plane modelled by an electric boundary condition. The input impedance of the antenna is calculated for different antenna mounting positions.

Figure 1: Monopole antenna geometry, excitation and boundary conditions

The position of the monopole is changed from the center of the box towards the edge and the corner of the box respectively. The admittance for the frequency range of 1-2 GHz is calculated using the Integral Equation Solver of CST MWS. This solver is based on a Method of Moments discretization and applies a triangular surface mesh. For electrically large structures the Integral Equation Solver includes an MLFMM algorithm, but since the total dimensions of this model are comparable to the wavelength the direct solver has been used....

Figure 2: Admittance (1/mOhm) vs. frequency of the monopole

Figure 2 shows the real and imaginary part of the admittance from measurements and simulation for various mounting positions from the centre towards the edge. The simulation results exhibit excellent agreement with the measurement.

Figure 3: Admittance (1/m Ohm) vs frequency for mounting positions between center and corner

Figure 3 compares the simulation and measurement results of the admittance for mounting positions between the centre and corner of the box. Again the results are in close agreement.

The Integral Equation solver has been applied to a simple monopole antenna structure and has shown excellent correlation with the reference measurement results.

References

[1] S. Bhattacharya, S. A. Long, D. R. Wilton, "The Input Impedance of a Monopole Antenna Mounted on a Cubical Conducting Box," IEEE Transactions on Antennas and Propagation, Vol. 35, No. 7, July 1987.