SWRA705 August   2021 AWR1243 , AWR1443 , AWR1642 , AWR1843 , AWR1843AOP , AWR2243 , AWR2944 , AWR6443 , AWR6843 , AWR6843AOP , AWRL1432 , AWRL6432 , IWR1443 , IWR1642 , IWR1843 , IWR2243 , IWR6243 , IWR6443 , IWR6843 , IWR6843AOP , IWRL6432 , IWRL6432AOP

 

  1.   Trademarks
  2. 1 Introduction and Challenges
  3. 2 Radome Design Elements
    1. 2.1 Understanding Dielectric Constant and Loss tangent on Radome and Antenna Design
    2. 2.2 Impedance Mismatch at Radome Boundaries
    3. 2.3 Radome Wall Thickness
    4. 2.4 Antenna to Radome Distance
  4. 3 Typical Radome Material Examples
  5. 4 Radome Angle Dependent Error
    1. 4.1 Rectangular Radome Angle Dependent Error
    2. 4.2 Spherical Radome Angle Dependent Error
    3. 4.3 Effect of the Angle Error in the Application
  6. 5 Radome Design and Simulations
  7. 6 Radome Lab Experiments
    1. 6.1 Radome Experiment – 1: Flat Plastic Radome
    2. 6.2 PTFE Material Rectangular Radome
    3. 6.3 PTFE-Based Curved Radome
  8. 7 Additional Considerations
    1. 7.1 Antenna Calibration
    2. 7.2 Radome Near Proximity Considerations
  9. 8 Summary
  10. 9 Acknowledgments
  11. 10References

2.1 Understanding Dielectric Constant and Loss tangent on Radome and Antenna Design

In order to understand the electromagnetic wave propagation in a material it is important to know the material constitutive parameters, such as, permittivity, permeability and conductivity. These constitutive parameters characterize the EM properties of the material. From these parameters, special care must be taken in selecting the radome material with optimum relative permittivity (Er) or dielectric constant (Dk). (Most radomes are designed out of a non-magnetic dielectric material such that the relative permeability = 1 and the conductivity = 0.) Signal fade or “loss” occurs either by the reflection of the electromagnetic waves at the boundary of radome structure or due to multiple reflections within the radome material itself. This is mainly due to the difference in dielectric constant (Dk) of the radome relative to air. The dielectric constant (Dk) represents the reflective, as well as the refractive, properties of a material. In general, the electromagnetic signal can be thought of as “slowing down” as it moves through the radome when compared with air.

Definition of loss tangent: Dielectric loss quantifies a dielectric material's inherent dissipation of electromagnetic energy. It can be parametrized in terms of either the loss angle δ or the corresponding loss tangent tan δ.

The dielectric constant and loss tangent together specify the transmission efficiency of a radome combined with an antenna system where both together are ideally measured at the intended operating frequencies. Dielectric loss quantifies a dielectric material's inherent dissipation of electromagnetic energy. It can be parametrized in terms of either the loss angle δ or the corresponding loss tangent tan(δ). The lower the dielectric constant and loss tangent, the smaller the effect of the radome on the antenna performance. Ideally Dk should be close to 1, since free space Dk is 1. However, it is impractical to use materials that have Dk=1 (basically Styrofoam) since they are not suitable for other goals of the radome (aesthetics, cost, and environmental robustness). Just to note that it is not the antenna design that forces Dk>1, but rather the radome material properties and availability.