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WideBand Dipole Antenna with integrated BALUN
Description
Dipoles have several applications in RF industry. One of the problems with dipole antennas, is the balanced nature of the dipoles which makes it difficult to feed them with a coaxial unbalanced line. Many people have had success in feeding a dipole directly with a coaxial cable feed rather than a ladder-line. However, coax is not symmetrical and thus not a balanced feeder. It is unbalanced, because the outer shield is connected to earth potential at the other end. When a balanced antenna such as a dipole is fed with an unbalanced feeder, common mode currents can cause the coax line to radiate in addition to the antenna itself, and the radiation pattern may be asymmetrically distorted.
Normally a separated media called BALUN is used to feed the dipole properly. In the following printed dipole antenna, the BALUN is integrated with the antenna using a tapered line to enable the user to connect the coaxial line directly to the antenna. The operating frequency of the antenna is 2.4 GHz. The butterfly shape technique is used to increase the bandwidth of the antenna.
Figure 1 - Helical antenna model (3D SolidWorks view)
Simulation
To simulate the behavior of this dipole antenna (radiation patterns and antenna parameters like gain, directivity...), we will create an Antenna study, and specify the frequency range (frequencies uniformly distributed from 1.8 GHz to 3.8 GHz). In an antenna simulation, radiation boundaries which are peculiar features of such a simulation have to be assigned to the outer air surfaces. These surfaces truncate the air surrounding the antenna and simulate an anechoic chamber.
Antenna studies of HFWorks afford multiple outputted results such as electrical parameters calculated in Scattering Parameters simulations (insertion, return losses...etc).
Solids and Materials
The antenna is built of a Duroid 5880 substrate and two Perfect Electric Conductor surfaces orthogonal to the port face. The whole structure is then plunged inside the air box.
Load/ Restraint
The port is applied to the lateral faces of both substrate (the side of the upper face of the PEC) and the air box. This way, the simulation considers the electric field's radiation in the air. RB (Radiaiton Boundaries) truncate the outer air box and simulate an anechoic chamber.
Meshing
Meshing the surfaces of the port and the printed patch helps the solver take their forms into account. Besides, for better results, the mesh element length shouldn't exceed one tenth of wavelength.
Figure 2 - Mesh of the dipole antenna
Results
Various 3D and 2D plots are available to exploit. The following figure shows the radiation pattern of the considered antenna at 2.3 GHz:
Figure 3 - 2D and 3D radiation patterns of the dipole antenna at 2.3 GHz
This figure shows conformal views (2D and 3D) of the variation of the power radiation pattern of the antenna in terms of the Theta angle. The 2D radiation plot shows the maximum of power radiated at the considered frequency; the angle corresponding to that radiation is obvious within the figure through the use of equipotential concentric circles spaced by 0.14 dB in this case. HFWorks automatically computes the maximum radiated intensity's properties (Theta, Phi, power, Directivity, Gain, Effective Angle, Radiation efficiency..)
As mentioned within the beginning of this report, HFWorks computes Scattering Parameters within antenna studies: Therefore, the return loss curve can be shown. In this example, the antenna is best matched at 2.3 GHz:
Figure 4 - Variations of reflection coefficient at the antenna's port
Figure 5 - Variations of the measured reflection coefficient at the antenna's port
Figure 6 - Near Electric field vector distribution