The BiQuad antenna is also known as "Trevor Marshall's antenna" in honor of who the first to propose its use in Wi-Fi networks in 2001. Director of the Autoimmunity Research Foundation, Professor Trevor Marshall (USA) is a qualified radio amateur. On his personal website, you can find a design description , which he used as a feed for a dish antenna. Our modern BiQuad antenna calculator for many "anonymous" is quite difficult to understand. Let's take Trevor Marshall's antenna as a simpler design and recalculate for 3G-4G networks...
Prof. T.Marshall used a 110x110mm reflector. However, he notes that if the antenna is used on its own, and not as a dish feed, then it is better to make a reflector with sides of 123x123 mm, i.e. equal to the wavelength of the Wi-Fi range. At the edges, the reflector has lips 30 mm high, which reduce the rear and side lobes of the antenna pattern by about 6 dB. The antenna was calculated in the 4NEC2 program, the model file for this program can be downloaded from us. A general 3D view of the radiation pattern for the Bi-Quad antenna, which gives out 4NEC2, can be seen in the figure. In the author's article, a tube is soldered behind the reflector, which serves only as a fastener and does not perform any special function. The author notes that if the structure is assembled carefully, then balancing devices are not required. Marshall suggests using 1.2mm wire. A large number of radio amateurs from different countries took part in the antenna test and came to the conclusion that the diameter of the wire to cover the entire Wi-Fi range should be taken more. The analysis shows that with an increase in diameter from 1.2 to 1.6 mm, the SWR at the center frequency increases from 1.14 to 1.22, which is insignificant, and the antenna gain decreases by 1 dB, which is also not much. In this case, the antenna covers all 14 Wi-Fi channels.
The calculated antenna gain is about 10 dBi, the input impedance is 50 ohms. Based on the NEC model, we have created an online calculator with which you can recalculate the dimensions of the antenna to other frequencies. Schematic representation of the antenna:
Source code Javascript:
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Limitations and features of antenna calculations
For example, here is one of the finished designs of the Prof. Marshall's antenna. The reflector is made of a duralumin sheet in the center of which an N-connector is mounted, and a figure eight is already attached to it.
In conclusion, I would like to draw your attention to the fact that the relative width of the Wi-Fi range is several times smaller than the UMTS-2100 range, and this design is not optimal for this and most other 3G/4G bands. Moreover, in Prof. Marshall's design, the issues of matching and balancing is completely ignored. These issues are solved in the our Modern BiQuad antenna online calculator and in the Dual-band BiQuad antenna design.
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