A collinear antenna array is made up of dipole elements. These dipoles are parallel and collinear with each other. This type of antenna has an enhanced gain and directivity in E-plane. Doubling the number of dipole elements, shall double the gain. However, practically it is usually less than that due to losses. In this example, a collinear array operating at 3.2 GHz is simulated with HFWorks.
Figure 1 - The antenna array
The antenna structure recalls the use of Franklin's principle in linking several radiating dipoles to sum up all radiations' intensities. Using 180° phase shifting between the dipoles to prevent destructive sums, the antenna can be implemented with other types of antenna dipole such as microstrip patch antenna.
All dimensions are in mm. The schematic shows only the linking between two of the three dipoles: The second link being exactly built of the same manner.
The feed of the antenna is located on the lateral face of one of its ends; the other end being an open circuit. Each dipole is treated like an insulating layer of Duroid 5880 substrate with PEC inner and outer conductor layers. All dipoles are plunged in an air box whose lateral surfaces simulate an anechoic chamber.
The mesh of this example must be accurate enough on the circularly formed dipoles so that the simulator gets that the models are pretty circularly shaped.
The meshing being realized, we run an antenna simulation in the frequency range from 0.5 GHz to 3.5 GHz to precisely visualize the behavior of the antenna around the intended frequency.
Figure 3 - Reflection coefficient at port 1
As we have seen in the dimension section, the full wavelength is about 100 millimeters which almost corresponds a frequency around 3 GHz. According to the curve above, we have reached a good level of return loss at 3.25 GHz: the curve keeps decreasing reaching an acceptable matching and proves the principle of the constructive sums of the three radiating dipoles. A figure of the radiated total field is shown further.
Figure 4 - Near electric field distribution
Figure 5 - Far field distribution
We can refine the angles' steps during the creation of the study to get smooth plots whether in 2D or 3D. In this figure, we have plotted the 3D radiation of the electric field.
This antenna has been optimized to respond to the specifications of the intended application, testing the precision and the principle of the Franklyn antenna; as we have seen, the antenna shows acceptable performances by operating within the right frequency range and with good levels on return loss around 3 GHz. Further tests for other Franklyn antenna types (such as mirostrip patch antennas) can be tested in HFWorks.