Example 2: Polar Plots of PCB LPDAs

Our antenna test service evaluated two PCB antennas designed by Kent Britain WA5VJB. They are both Log Periodic Dipole Array (LPDA) antennas designed for the following ranges:

• Antenna “2A” Operating Range 400 – 1000 MHz
  • Evaluated 300 – 1300 MHz (every 10 MHz, 101 frequencies)
  • 2D polar cuts in the E and H planes with 2 degree resolution
• Antenna “2B” Operating Range 2 – 12 GHz
  • Evaluated 700 MHz – 18.5 GHz (every 100 MHz, 251 frequencies)
  • 2D polar cuts in the E and H planes with 1 degree resolution

LPDA antennas are not the same as Yagi antennas, and they are a compromise arrangement of shrinking elements designed to cover a broad range of frequencies. The designer tries to minimize the number of elements to save space, without leaving “gaps” in the operating range which occur at frequencies in between the operating lengths of the actual elements. In a Yagi antenna, all elements operate together in one narrow band of frequencies.

Results

• Antenna “2A” Operating Range 400 – 1000 MHz
  • Typical forward gain of 5 to 8 dBi over the intended operating range
  • Front-to-back ratio changes dramatically with frequency, but is typically better than 10dB
  • Graphs of Gain and F/B vs frequency are shown, as well as some spot frequency polar plots
• Antenna “2B” Operating Range 2 – 12 GHz
  • Typical forward gain of 2 to 6 dBi over the intended operating range
  • Graphs of Gain and F/B vs frequency are shown, as well as some spot frequency polar plots

As always, since all data is recorded in spreadsheet format, additional plots and post analysis is always possible. All pictures are “click to enlarge”.

Test Report and Photographs for Antenna “2A” 400 – 1000 MHz

Downloadable Excel results (all gain data and polar plots) available HERE

Test Report and Photographs for Antenna “2B” 2 – 12 GHz

Downloadable Excel results (all gain data and polar plots) available HERE