Back in January we posted about a Vivaldi antenna project by "hexandflex". In that project he showed how he designed and manufactured the Vivaldi. A Vivaldi antenna is wideband and directional and the design works well for frequencies above 800 MHz, but becomes too physically large to handle for lower frequencies like 400 MHz. In his latest project, hexandflex has designed a PCB based spiral antenna to cover these lower frequencies.
Hexandflex is currently selling his spiral antennas over on Tindie. There are two versions, one smaller one costing $32 designed for 800 MHz+ and a larger one costing $42 designed for 300 MHz+. Both come with suction cups that allow for easy window mounting.
The Vivaldi is a fairly well known ultra wideband antenna that is directional. It is fairly easy to build out of a PCB board, but requires some careful design considerations to work well. In the second post hexandflex goes over all the design considerations that he put into his Vivaldi incliding the feed design, substrate choice and additional improvements like adding corrugations and crafting the geometry for a lens effect.
The results show that the antenna works well as a directional antenna above 1.7 GHz, and begins to work more like a standard dipole below 1.7 GHz. Directional gain is greater than 5dB above 1.7 GHz, and becomes negative below 1 GHz. Although hexandflex notes that the gain below 1 GHz is still reasonable, and probably still better than any untuned monopole.
Hexandflex has put up a small number of Vivaldi antennas that he's produced up for sale on Tindie for US$18. Currently he has a limited batch of units to sell, but notes that he may run additional batches if they are popular.
Vivaldi’s are linearly polarized broadband antennas that have a directional radiation pattern at higher frequencies. The high end SDR manufacturer RF Space produces their own Vivaldi antennas made from PCB boards which they sell online. The larger the antenna, the lower its receiving frequency, and ones that go down to about 200 MHz are almost the size of a full adult person. But all sizes receive up to 6 GHz maximum. Typically smaller versions of Vivald antennas have been used in the past for L-Band satellite reception.
Over on his blog KD0CQ noted that he always had trouble trying to purchase a Vivaldi from RF Space because they were too popular and always out of stock. So he decided to try and build his own out of PCB boards. On this page he’s collected a bunch of Vivaldi cutout or transfer images. On his second page he shows a Vivaldi antenna that he built out of PCB material, just by using scissors and semi-rigid coax. With the Vivaldi placed outdoors he’s been able to successfully receive and decode L-Band AERO on his Airspy Mini even without an LNA.
KD0CQ writes that he’ll update his blog soon with more results.