Vivaldi antennas can provide excellent directional propagation at microwave frequencies. As introduced in Part 1 of this article, the Vivaldi antenna can be a simple design based on a tapered-slot-antenna (TSA) architecture. This concluding installment in this two-part article will compare measurements of a designed and fabricated X-band antenna with simulations from the Advanced Design System (ADS) software from Agilent Technologies (www.agilent.com).

The eight-point design and simulation process using the Agilent Momentum EM analysis tool from Agilent's ADS software suite was detailed in Part 1. The antenna was fabricated on RO4003C material and an SMA end-launch connector was affixed to the microstrip line of the antenna. The outer ground pins of the SMA receptacle was shorted to the slotline ground planes of the antenna while the SMA's center pin was soldered to the stripline transmission line. Figure 5 shows a Vivaldi antenna board fabricated in this manner, ready for testing and evaluation.

Measurements include generating S-parameters and radiation patterns. Figure 6 shows an example test setup for evaluating the S11 parameters of the Vivaldi antenna.

Before making measurements, the vector network analyzer (VNA) must be calibrated. Then, connections are made from the Vivaldi antenna's 50-ohm connector and the VNA's port 1 connector by means of a 50-ohm low-loss coaxial cable. The VNA is set for measurements from 8 to 12 GHz.

Once the S11 log magnitude results are obtained from the VNA, they can be compared with the simulated results from the Momentum analysis. By this comparison, an optimum frequency of 9.20 GHz was found for the radiation pattern measurements. The test setup used for the radiation pattern measurements is shown in Fig. 7.