10-2: IEEE Microwave Theory and Technology Society at Texas A&M University

Written by Denisse Alvarez, Sai Gudavalli, Mathew Klein, Zaafir Siddique, Roman Venegas, Daniel Wen

IEEE Microwave Theory and Technology Society at Texas A&M University, also known as MTT-S TAMU, is a student chapter that helps aspiring engineers learn about microwave theory and supports students tackling challenging microwave engineering projects. The M.T.T. Heracles is MTT-S TAMU’s first Satellite Communication Project that has 7 Aggies working together to build a nested helical antenna to communicate with amateur radio operators using the International Space Station (I.S.S). The team is preparing the M.T.T. Heracles for its maiden voyage in Fall 2026. With the use of Cadence AWR software products, the team hopes to make a robust antenna system for multiple successful radio contacts with the I.S.S.

Constructing the M.T.T. Heracles began with simulating and designing 2 helical antennas with operating frequencies at 430 MHz and 145 MHz. The selected helical antenna frequencies were chosen to properly perform FM downlink and uplink with the I.S.S.’s onboard repeater. Each antenna was built using copper wire wrapped around two cylindrical structures supported by a 3D printed holder and a 1 meter in diameter ground plane. To minimize coupling, the copper wires were wrapped in opposite directions when constructing the helicals.

Each helical antenna’s operating frequency is controlled by the circumference of its turns. If the circumferences of the two helicals are equal to the wavelengths of 435 MHz and 145 MHz, then the helicals will be directional, circularly polarized antennas. Given that the 145MHz helical antenna has a diameter of approximately 60cm, the team was able to “nest” the 430 MHz helical antenna within the 145MHz helical, giving the M.T.T. Heracles its dual band capabilities. The M.T.T. Heracles currently uses a 3D printed frame piece that supports both helicals and attaches them to the ground plane.

The inner cylindrical structure for the 430MHz helical was made using matte poster paper, while the outer cylindrical structure was made out of embedded PVC pipes that gave shape to the 145MHz helical. Copper wire was then wrapped around both cylindrical structures with calculated pitch angle and spacing so that each helical antenna achieved targeted directivity, half-power beam width, circular polarization, and radiation pattern. Furthermore, the ground plane at the bottom is wrapped in aluminum foil and acts as a reflective surface that helps the M.T.T. Heracle direct all the radiated power in the desired direction.

To interface our dual-band nested helical antenna with the transceiver front end, our team needed 2 impedance matching networks for both frequencies. We used a temporary solution of a piece of aluminum wrapped around the antenna’s connectors to act as a stub matching network, varying its dimensions to decrease S11 reflection. However, this gave only slightly better results than no impedance matching, achieving 90% transmission, -10 dB S11 loss for both frequencies. In order to achieve better S11 measurements, AWR software was used to design and simulate lumped element L-shaped matching networks to match our 145 MHz and 430 MHz helical antennas.

Since each board addressed a single frequency, we treated the matching problems with respect to each antenna. We synthesized component values in AWR software and used the provided simulation to tune our inductor and capacitor values against S11 and S21 parameter plots. Further capabilities were explored by employing the optimization function to determine a better impedance match for our S11 parameter. The final simulated designs achieved an S11 measurement of approximately -50 dB at each target frequency, and around -20 dB within a wide frequency range.

After designing both matching networks in AWR software, the PCB layouts were exported as a Gerber file and used to create a CAM design for CNC fabrication. The CAM design included two contour toolpaths around the traces to precisely remove the surrounding copper and isolate the transmission lines. A square pocket was then machined around the exterior of the traces to remove the remaining excess copper, and a final outer contour was used to cut the completed PCB out of the larger copper-clad board.

Once the PCB was fabricated, SMA connectors were soldered onto each end of the board. The final step will be to solder the surface-mount inductors and capacitors onto the PCB, completing the physical implementation of the matching networks originally designed and optimized in Cadence AWR software products.

Cadence is proud to support the MTT-S TAMU team, they’re making an impact in training the next generation of innovators with the hands-on experience they need to excel in their future careers.