Function of Component

The antenna will be used for telemetry and command, communication, and navigation.

Key Parameters

The following parameters were used in making a selection:

• Directivity
  • This parameter determines whether the antenna receives signals equally from all directions (omnidirectional) or receives signals better in a certain direction (directional).

• Antenna Type

  • There are various types of antennas ranging from dish antennas to patch antennas.

• Frequency

  • Number of cycles per second
  • Units: Hz (hertz)

• Gain

  • How strong the antenna is to send or receive a signal in a certain direction. The higher the gain is, the more concentrated in a certain direction the signal is. The lower the gain, the more omnidirectional the antenna is.
  • To calculate this value, the power transmitted or received in a certain direction by the antenna is compared to the power transmitted or received in that same direction by an ideal antenna.
    • If the ideal antenna equally transmits or receives energy in all directions, then the unit of measurement is dBi.
    • If the ideal antenna is a half-wave dipole, the unit of measurement is dBd.
  • An antenna that equally transmits or receives energy in all directions would have 0 dBi.
  • A positive gain amplifies the signal, while a negative gain reduces the signal.

• Voltage Standing Wave Ratio (VSWR)

  • How closely aligned the impedance of the antenna is to the impedance of the radio or transmission line it’s connected to. The more similar the impedances are, the more power the radio is able to deliver to the antenna.
  • A small VSWR value indicates the impedances are more closely aligned, with 1 being the minimum value possible.
  • Equation for VSWR is below, where Gamma (Γ) is the reflection coefficient

  

  • Standard is VSWR = 2

• Reflection coefficient

  • The amount reflected from an electromagnetic wave caused by a discontinuity in impedance in the method of transmission.
  • Preferably, the closer to negative infinity the relation coefficient is, the better. While that’s not possible, -20 dB is a very good value, while -10 dB is a standard of good matching. A mismatch is anything above -10 dB.
  • Equation for reflection coefficient is below, where |S_11| is the reflection coefficient

  

• Size

  • Dimensions of the antenna

• Price

  • How much the antenna costs

Selection Criteria

Values being considered for the antenna:

• Directivity: Omnidirectional
• Antenna Type: Patch Antenna
• Frequency: 430MHz - 450 MHz
• Gain: the closer to 0 dBi the better
• VSWR: the closer to 1 the better