Wire Antennas

Introduction

WIPL-D Pro is a Method of Moments (MoM) tool which is using bilinear quads and wire segments as mesh elements. Higher order basis functions are used on both plates and wires, meaning that wire segments can be up to 2 wavelengths long. Using wires gives a significant advantage for modeling wire-like structures since wire numerical models are much more simple than plate models. Very large wire structures can be simulated in a matter of seconds or minutes on an ordinary PC.

Wires are often used to model simple antennas like monopoles and dipoles placed on large platforms, a situation in which higher order MoM used in WIPL-D Pro excels. Wires are also used to build helix antennas, which are displayed here in a separate chapter.

Wires are not meant to be a replacement for plates in surface modeling (although this is possible) and that's where WIPL-D Pro differs from wire-grid tools like the well-known NEC. Using plates for surfaces is a much more efficient approach.

Example: Yagi-Uda Antenna

Yagi-Uda (further Yagi) antenna is array of dipoles. Radiation of all elements is summed in forward direction. Yagi antennas are used in radio links for computer networks (Wi-Fi). Some kinds of Yagi are used for receiving TV and FM radio signals.

Main characteristics of Yagi antennas are

  • Gain 5-16 dBi,
  • Narrow-band (relative bandwidth is ~10%).

WIPL-D Simulation

Models of Yagi antennas simulated in WIPL-D Pro are presented here. Simulated Yagi antenna consists of one reflector, one fed dipole and ten directors. One model is made of wires, while the other model is made of plates. Wire antenna is shown in Fig. 1, while the plate antenna is shown in Fig. 2 and the feeding area is zoomed-in in Fig. 3. Dimensions of both models are the same. That means that every wire in wire model is replaced by body of rotation and terminated using circle object in the plate model. We will assume that given antenna is used in B-band (NATO band classification).

Our aim is to compare simulation times for wire and plate antenna models and show that wires are viable building blocks for many antenna types for which they can speed-up the simulation significantly.


Figure 1. Yagi antenna modeled with wires


Figure 2. Yagi antenna modeled with plates

In WIPL-D Pro, iterated structures can be designed using convenient built in features. Antennas shown on Fig. 1 and Fig. 2 can be modeled in several ways but the optimum way is to use (Anti-) Symmetry feature and Copy/Move manipulations to facilitate modeling. Metallic parts are considered to be perfectly conducting. Operating frequency is 266 MHz (B-band).

Table 1. Analysis characteristics

Model No. of unknowns Time @ 266MHz [sec]
Wires 36 0.0056
Plates 1560 12.5

Radiation pattern in 3D is shown in Fig. 4. Overlaid 2D radiation patterns for a theta-cut are shown in Fig. 5. As can be seen, there is no difference in calculated radiation pattern regardless of what type of geometrical entity (wires /plates) is used in the model.

Near field of the wire model is given in Fig. 6.

Number of unknowns and simulation time of analysis are given in Tab. 1. Computer used for these calculations is Intel® Core(TM) i7 CPU 950@3.07 GHz.


Figure 3. Yagi antenna modeled with plates –
feeding area and plate approximation


Figure 4. Radiation pattern of Yagi antenna made of wires


Figure 5. Overlaid 2D radiation patterns for theta cut


Figure 6. Radiation pattern of Yagi antenna made of wires

Conclusion

We conclude that using wires to model a Yagi antenna leads to great diminishing of simulation time and number of unknowns. Various types of structures can similarly be simulated using wire models, and not plate models. Wires can be used to model cylinders whose radius is up to 0.1λ and whose length is much larger than the radius. In those cases, simulation is faster hundreds of times, and memory usage can even be thousands of times lower.

PDF application note

If you have a specific problem in mind and you are not sure if WIPL-D software can handle that problem, contact us. We will analyze your needs and try to help, and if our products satisfy your requirements, we will make you the best possible offer for purchase.