The main information required for the design of DRA is the radiation field, resonant frequency, bandwidth, resonant modes inside the DR structure, radiation Q-factor and field distribution [3, 16]. The design and simulations of the DRA antenna can be carried out using software packages like FEKO, Empire XCcel, HFSS and CST Microwave Studio suite. The simulated antennas then can be fabricated using a photolithographic method. Real-time measure of S-parameter/VSWR characteristics is done by a network analyzer. The real-time antenna gain and radiation patterns can be computed in anechoic chamber. Full wave solvers use either analytical or numerical methods for getting the solutions. The analytical methods give the exact solution, and they include variable separation, expansion in series, conformal mapping, integral solution (e.g., Laplace and Fourier transformation) and perturbation methods. Numerical methods give approximate solutions, and they include finite difference method [time domain approach], method of moments (MoM) [frequency domain approach], finite element method (FEM) [frequency domain approach], finite integration technique (FIT) [time domain approach] and transmission-line modelling [time domain approach],

HFSS uses FEM and thus gives more accurate results while designing antennas. CST uses FIT, and it provides the designer ease in simulations. Results of both the simulators are not identical due to the use of the different computational technique. On the one hand, HFSS results are nearer to experimental results, with more emphasis on the structure available. On the other hand, in CST, perfect boundary approximation (PBA) can be done and it is suitable for 3D antenna simulation. The FEM methods provide solutions in the frequency domain, while the FIT methods give solutions in the time domain. FEKO uses the MoM method. The MoM can be used in combination with the geometric optics approach (GO), the unified theory of diffraction (UTD) and the multilevel fast multimode method (MLFMM). It can genuinely model arbitrary 3D structures. With the FE method modelling of dielectric volumes can be done with an SIE approach or VIE approach or with a hybrid approach.

Empire XCcel uses the finite-difference time-domain (FDTD) technique. Due to adaptive on-the-fly code generation, it comes with a highly accelerated kernel, providing very fast simulations. It gives more accurate results for curved structures by the perfect geometry approximation (PGA) algorithm. It also provides frequency- dependent loss calculation and special algorithms for modelling thin conducting sheets. Selection of antenna design software depends on the structure’s geometry and the intended accuracy of the solution. For example, ZELAND IE3D uses MoM solution, which provides brilliant analysis accuracy for the frequency domain, but it cannot admit very fine details on the geometry of the structure. Hence for simple structures like rectangular or circular, IE3D would be the best. ZELAND Fidelity uses FDTD analysis. It uses a combination of specific geometries. It is mainly suitable for regular shapes like cylindrical DRA for an example. MoM and FDTD methods are not desirable for big structures like large antenna arrays or reflector antenna. Ansoft HFSS and CST provide a better interface to allow very fine inside information regarding the geometry of the simulated structure. HFSS uses FEM, and CST uses FIT, which is similar to FDTD. Both methods are preferable for small or moderate objects in comparison with the working wavelength.

CST provides the advantage of getting the results on a wideband as it begins in the time domain and changes the results to FD through Fourier transform. Dissimilar operations are found in HFSS, though they are FD solution. Accuracy of MoM is slightly more than the accuracy of finite element. Thus results in HFSS and Zeland IE3D differ slightly for regular shapes like rectangular patch antenna. In this case the result of HFSS is less accurate than Zeland IE3D. But in the case of complicated geometry, the accuracy of HFSS and CST are much better than IE3D due to the geometrical approximations taken for the structure.

FEKO has two main solvers, based on MoM and geometrical theory of diffraction (GTD). The portion of FEKO related to GTD cannot be substituted with Zeland, HFSS or CST because it is basically meant for large structures similar to reflector antennas. To summarize the debate over antenna algorithms, a good designer must be able to use different computer-aided design (CAD) tools with clear understanding of the bounds of their numerical techniques and modelling interface. Recently CST has gained popularity. But with inappropriate tool settings, the problem of ripple in the frequency response may occur. Using HFSS and CST requires a good knowledge of the numerical techniques they use; that is w'hy most users get incorrect results, especially w'hen the error is concerned with feed modelling and source-port definition. This software can simulate very large structures depending on the available hardware resources. For some structures, HFSS is faster and leads to better results, while CST may be better for some other structures [17, 18].

DRA Design Algorithm Steps in HFSS

  • • Start.
  • • Open HFSS software.
  • • Insert geometrical project design.
  • • Form basic fields. (Assign material for each element, radiation boundary for the structure and then give the required excitation.)
  • • Discretize the finite element and form the surface integral for fields. (In the analysis setup assign frequency sweep range and solution frequency, then run and analyzed the results.)
  • • Stop.

DRA Design Algorithm Steps in CST

  • • Start.
  • • Open CST Studio Suite software and select ‘New Project’; then click ‘Create Project Template’; then select ‘Antennas’ under the option ‘MW & RF & Optical’. Then click on ‘Dielectric Resonator’ from workflow.
  • • Then select ‘Solver’ in time domain to enter fields in time and spatial domain. (Select dimensions, frequency, time, temperature, voltage, current, resistance, conductance, inductance, capacitance.)
  • • Implement Yee’s algorithm by selecting field settings (Freq Min, Freq Max,

E & H Field, Far Field, Pow'er flow and loss).

  • • Estimate cell size and time step.
  • • Analyze the dielectric resonator antenna by providing source signal and feed modelling.
  • • Cut short the computational area by a virtual limit, and then run and analyze the results.
  • • Stop.

DRA Design Method in MATLAB

In MATLAB analysis, the resonant frequency and the unloaded Q-factor are calculated. Then estimation of the bandwidth of various resonant modes of a dielectric resonator placed on an infinite ground plane is done. The resonator dimensions are set according to the input specifications on aspect ratios, resonant frequency, resonant mode, minimum bandwidth, dielectric constant, etc. The user can quickly find the resonator dimensions in the design mode. MATLAB software provides supports for analyzing and designing various resonator shapes like hemispherical, cylindrical, cylindrical ring and rectangular cross-section. Optimization of antenna design can also be done with MATLAB. All the simulations of E-field, H-field, far-field can also be done in MATLAB, as can be done in HFSS and CST. The difference lies in writing your own MATLAB programmes using the MATLAB toolbox [19].

< Prev   CONTENTS   Source   Next >