Antennas

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1 General Information

General rule of thumb:

  • The higher the frequency the smaller the antenna.
  • For the special case of patch antennas: The more antenna patches placed, the narrower the beam width.
  • Connections from IC to antennas such as bond wires etc. causes impedance mismatch, decreasing efficiency and bandwidth. This has to be matched again during antenna design. The smaller and less tolerant the structures, the easier the matching (for example an antenna on chip is easier to match compared to an antenna on PCB).

2 External Antenna

Any external antenna that is commercially available, can be used for sensor designs using Silicon Radar ICs. The challenge of using such antennas is the transmission of the signal to the antenna from packaged IC, especially for very high frequencies. Therefore, it is generally common to use such antennas only for 24 GHz products.

Advantages:

  • Various antenna types from various suppliers
  • Commercially available, no special design required

Disadvantages:

  • Hard to find for higher frequencies
  • Transmission to antenna has high loss for higher frequencies, especially over the connectors
  • Not suitable for high bandwidths

3 Antenna on PCB

Antennas can also be designed directly on a high frequency PCB. RF-PCB materials are normally verified up to 110 GHz; however successful designs are also possible at 120 GHz ISM band.

24 GHz antennas on PCB
24 GHz MIMO antennas on PCB

Advantages:

  • Flexible antenna designs are possible since the area is not limited as in case of antenna on chip or on package
  • Cheaper for prototyping compared to antennas on chip or on package
  • Antennas can be placed very close to the IC on PCB, so transmission from IC to antenna can be efficient
  • Suitable for 24 GHz and 60 GHz designs

Disadvantages:

  • Long bond wires may limit the performance (depends also if bare IC is directly wire bonded to PCB or already in a package)
  • Standard PCB technology is limited, also limiting the matching structures of antenna designs resulting less efficiency at higher frequencies
  • Standard PCB tolerances are high, increasing the center frequency shifts of final designs
  • Not suitable for extremely high bandwidths
  • RF-PCB material is expensive

4 Antenna in Package

Antennas can also be placed directly in high frequency package. This increases the choice of materials and technologies (for example thin film) to design antennas. But in this case, the area may be limited, if compared to antennas on PCB. Successful designs are possible up to 160 GHz and above.

120 GHz chip (TRX_120_001) with antennas in package
60 GHz antennas in package

Advantages:

  • Long bond wires will not be an issue, since flip-chip technology can be used
  • Flexible for new designs
  • Antenna can be placed very close to the IC increasing efficiency
  • Very suitable for 60 GHz and 120 GHz designs
  • Cost-effective solution in series production

Disadvantages:

  • Antenna area may be limited, also limiting antenna performance
  • Expensive for prototyping
  • Not suitable for extremely high bandwidths

5 Antenna on Chip

Antennas can be placed directly on Silicon IC. This allows very fine structures down to few microns size, however the total antenna area is limited. High performance integrated antenna structures are possible up to THz-range.

120 GHz Phased Array antennas on IC
High bandwidth 300 GHz antenna on IC (TRX_300_030) combined with silicon lens on package

Advantages:

  • Antennas are directly connected to IC structures allowing maximum efficiency
  • Suitable for 60 GHz to THz designs
  • Suitable for high bandwidths
  • Not very expensive in series production

Disadvantages:

  • Antenna area is limited, therefore narrow antenna beams are not possible
  • May be more expensive for prototyping
  • Not suitable for low frequencies such as 24 GHz