The Crazy Lune - Astronaut to RFID Antenna

			The Crazy Lune

Astronaut to RFID Antenna

The overall design for the proposed radiolocation system requires a separate antenna for the bidirectional wireless link between the astronaut and the RFID tags. The radiolocation system is more effective if the astronaut-tag link does not interfere with the astronaut-lander link. Given the freedom to operate with impunity throughout the 1Ghz to 3Ghz spectrum, the most straightforward approach is for the two links to operate on entirely separate bandwidth. Therefore, the astronaut-tag antenna must also be different than the astronaut-lander antenna.

There are two primary considerations for designing the astronaut-lander antenna. Since the RFID tags can be located anywhere around the astronaut, the antenna must be omnidirectional. Also, in order to maximize other link budget considerations, the antenna should have peak gain at the lowest possible frequency.

A half-wave dipole antenna is omnidirectional and has reasonable gain. The antenna was designed and simulated using the NEC2 program. Figure 1 shows the results of our simulation for a half-way dipole antenna that experiences peak realized gain at 1.031Ghz. The center frequency of 1.031Ghz was chosen because it is the lowest center frequency that does not drop below the lower design limit of 1Ghz with 3% bandwidth

Figure 1. Omnidirectional gain pattern.

The antenna is 0.067m in one direction and 0.067m in the opposite direction. The wire is 0.001m thick. The voltage is applied in the center of the wires. The FR and RP lines are used in the plotting programs to plot the gain at 1.031Mhz at locations all around the antenna, as shown in Figure 1. Those lines can be modified so that the gain is measured from one location for multiple frequencies, as shown in Figure 2.

Figure 2. Realized gain at center frequency.

The figures are generated using plotting programs provided, along with the NEC2 program itself, on Professor Waymond Scott’s website(http://users.ece.gatech.edu/wrscott/).The gain of the designed astronaut-tag antenna is 1.997dBi.

Tuesday, December 8, 2009