Home

What is a VHF Antenna? It is a device made to transmit and receive radio frequenies at the very high frequency (VHF) radio wave range. The VHF frequency range -- 30 to 300 MHz -- is commonly used to transmit television broadcasts and FM radio. However, in our project, our motivation is to design a self-deploying VHF antenna to integrate into a low cost, low power radar system designed to detect stealthy, low altitude, high speed, targets. We seek to implement a continuous wave radar system that can be deployed as on a series of fence-posts, with little-human installation.

Qualitative Requirements

  • Low Cost
  • Low Power
  • Operate in VHF Band
  • Detect low-RCS Targets
  • High Reliability and Low Maintenance

    • Quantitative Requirements


    Deliverables

    Technical Review Papers

  • Mohammed Deafalla
  • Kenneth Holder
  • Seunghwan Lee
  • Seidi Kartal
  • Sanket Sane

    • Project Proposal

    Project Summary

    Proposal Presentation

    Final Presentation

    Final Written Report

    Final Video

    Design Prototype

    This is our design approach that we came up with to successfully implement our design of the VHF antenna.

    The Ideal Antenna

    • Modeled an antenna using ideal and desired antenna parameters
    • Gain – High enough to allow for low power signals on small RCS
      • G0 = 8 dB
    • Radiation Pattern – covering the upper hemisphere equally
      • D α sin(θ) |0<θ<π
    • HPBW – Wide coverage that avoids ground scatter
      • 160°
    • S11 ⩽ -20 dB
    • SLL = −20dB
    • Zin = 50Ω

    Antenna Design Geometry

    We had two choices of antenna design geometry to choose from.

    Plan for Design

    Costs for Fabrication

    We later realized that we would need some kind of bracing mechanism to support the monopole rod.

    Bracing Mechanism

    The bracing mechanism was 3D printed using PLA material here in the invention studio, so there are no added costs.

    Simulation Results

    Antenna Simulation Results Ver. A

    Antenna Simulation Results Ver. B

    We ended up choosing to continue with version A.

    Simulation Report

    Radiation Patterns

    Effect of Brace Mechanism

  • Minimal effect on gain
  • Significant effect on return loss and input impedance

    • PLA Dielectric Constant

    Return Loss with εPLA, 10%

  • Improved S11
  • However, resonant frequency is not at 224 MHz
  • By shortening the rod by 0.01𝜆 (951mm), resonant frequency is shifted to 224 MHz
  • Minimal impact on gain

    • ADS Simulation of Electronic Circuit

    Material and Fabrication

  • Aluminum 6061​
  • Polycarbonate Sheet​
  • 3D Printed Brace​​

    • Aluminum Rod -- Antenna

    • Aluminum 6061​
      • Best conductivity in the budget category​
      • Lightweight, Cheap, and Weather Resistant​
      • 6ft long​
        • Need only 950mm​
        • The rest is experimental stock​
      • 1-5/8 in diameter​

    Aluminum Sheet -- Ground Plane

    • Aluminum 6061
      • 4ft x 4ft area​
      • 0.04in thick​
        • Too expensive to get thicker aluminum
        • Need just the surface​
          • Will have supporting material​

    Polycarbonate Sheet – Supporting Material

    • Clear Impact-Resistant Polycarbonate
      • 4ft x 4ft area
      • 1/4in thick
      • Acts as the support for the thin Aluminum Ground Plane

    3D Printed Brace

    Another Angle of Antenna Construction

    Fully Constructed Antenna

    Test Results

    We used a network analyzer to perform an S11 measurement on the constructed antenna.

    Comparison of Simulated vs Experimental Results

    Analysis of Results

    • Resonant Frequency (fr) is at desired frequency of 224 MHz
    • However, S11 at fr is significantly lower than expected
      • -22 dB vs -19 dB
      • We theorize this is due to a poor electric connection between the RF connector and the radiating element
      • Initially, we decided against soldering the prototype because it would make its transportation difficult between machining areas and lab

    Designed vs. Ideal Comparison

    Future Steps

    • Improving Electrical Connectivity
      • Placing set screws in brace to apply more pressure to rod
      • Soldering RF connector pin to rod
    Project Poster