RF Systems Lab

Lab 6: Square Loop Antenna

6.1 Square Loop Antenna

For a given frequency, the gain of a loop antenna is less than a well-designed dipole antenna. But the output voltage can be increased by adding a capacitor (in our case, a trimmer capacitor1) to the primary windings, thus creating a resonant structure. Here, the loops provide the inductance. The antenna is first oriented so that the magnetic fields from the transmitting station passes normally through the loops. Then the antenna is tuned (i.e. the resonance frequency is adjusted) by adjusting the trimmer capacitor. The pre-lab report for chapter 6 can be found below.

6.1 Antenna Construction

For this lab, a Little Caesar's pizza box with a diagonal of approximately 20in was used as the frame. Using the MatLAB program from the pre-lab report, it was determined that 16 loops would be needed to achieve the necessary inductance for 1400kHz. After modifying the program to fit the specifications of the pizza box, the capacitance for Auburn's 1230kHz station was determined to be 55.74 pF, which was achievable by the trimming capacitor. The spectrum analyzer was then used  verify the function of the antenna. Figure 1 shows the spectrum analyzer reading for the antenna at 1230kHz.

Finally, the antenna is connected to the radio, and a faint, but presence, radio station signal is heard.