WA5VJB Microwave Antenna Experiments |
Overview
Wideband antennas for Technical Surveillance Countermeasures (TSCM) or amateur radio applications tend to be very expensive or difficult to find. Thankfully, we can overcome this as Kent Britain (WA5VJB) sells several different wideband directional antennas aimed at the amateur radio market.
Covered here will be three of his models, the 850 - 6500 MHz log-periodic printed circuit board antenna, the 2 - 11 GHz log-periodic printed circuit board antenna, and the 10 - 25 GHz Vivaldi printed circuit board antenna. All these antennas can be purchased via eBay for under $15.
As these antennas will be used mainly for TSCM (bug finding) purposes, they will need to have semi-rigid SMA pigtails attached to allow the insertion of a wideband diode detector. This, in turn, will make the antenna act as a wideband field-strength meter.
By monitoring the DC voltage output level from the diode detector you can determine the relative distance to the hidden transmitter or RF source. The higher the voltage output, the closer to the RF source you are. This is a wideband detector, so there will be no frequency selectivity without adding additional RF filters to the antenna.
The diode detector used for this project is a HP 86290-60045, which can be salvaged from old HP oscillator RF plug-ins. They list their operating frequency range as 2 - 18 GHz, but they'll work over a much larger frequency range. The voltage output (often called the 'video' output) from these detectors is "negative going," which is an industry standard. Be sure to take this into account if you wish to further process the voltage output. The HP 86290-60045 uses a "SMC" connector on the output so a SMC adapter may be required, depending on your requirements.
A right-angle SMA socket should be used on the 850 - 6500 MHz log-periodic antenna, but the higher-frequency range antennas should have a short semi-rigid coaxial jumper directly attached to them for minimum frequency loss and maximum performance.
Pictures & Construction Notes

Overview of the three WA5VJB antennas, a couple of Hewlett Packard 86290-60045 2 - 18 GHz diode detectors with a SMC-to-SMA adapter, and the UT-085/RG-405 semi-rigid coaxial cables with SMA female connectors which will be salvaged to make pigtails.

Closeup overview of the solder connections required for the 850 - 6500 MHz (left) and 2 - 11 GHz (right) log-periodic antennas.
A right-angle SMA jack will be installed on the 850 - 6500 MHz antenna.
A short semi-rigid UT-085/RG-405 pigtail will be added to the 2 - 11 GHz antenna.
UT-141/RG-402 semi-rigid will work, but the smaller diameter of the UT-085/RG-405 coax will make it much easier to solder.

Installing the right-angle SMA jack. Be sure the connector uses a high-quality Teflon insulator and the installation is flush and well soldered.
All the antennas are at a DC ground so you can't really test them with a ohm meter when finished, so solder carefully.

Completed 850 - 6500 MHz log-periodic antenna with a HP 86290-60045 detector (and SMC adapter) attached.
You may want to experiment with a easy method to hold or point the antenna. Try some type of mounting bracket on the rear. Also try not to block the antennas radiation pattern it with your hand.
This antenna has a gain of around 6 dBi over its entire frequency range.

Make and attach the RG-405 pigtail to the 2 - 11 GHz antenna like so.
You'll want to trim the center conductor to the absolute minimum length.
Solder along the entire length of the shield of the RG-405 pigtail to properly secure it.

Completed 2 - 11 GHz log-periodic antenna with a HP 86290-60045 detector (and SMC adapter) attached.
This antenna is easier to hold and point as you can just grasp it via the detector's body.
This antenna has a gain of around 6 dBi over its entire frequency range.

Attaching a RG-405 pigtail to the 10 - 25 GHz Vivaldi.
This one is a little more tricky... Again, trim the center conductor as small as you can, then install the pigtail by "bridging" the gap within the antenna. Do this as close to the rear circle as possible.
Solder along the shield of the RG-405 and then route it behind the antenna, as shown.

Completed 10 - 25 GHz WA5VJB Vivaldi antenna with a HP 86290-60045 detector (and SMC adapter) attached.
This antenna is quite thin, so be very careful when handling it!
This antenna has a gain of around 8 - 10 dBi over its entire frequency range, and with a bit of luck is usable to around 40 GHz.
850 - 6500 MHz WA5VJB Log-Periodic Antenna Datasheet


2 - 11 GHz WA5VJB Log-Periodic Antenna Datasheet

10 - 25 GHz WA5VJB Vivaldi Antenna Datasheet

