Cavendish and Antenna Tuning

 Several trends in the phone market are increasing the difficulty of designing antennas for mobile devices, including:

  • Increasing number of frequency bands the phone supports – from today’s 4 or 5 bands to more than 12 bands expected by 2012.
  • Shrinking size allocated to the antenna (remember the telescoping antennas of yesteryear?).
  • The industrial design of smartphones, where the screen takes up nearly all the area and sometimes the case is made of metal – effectively blocking all RF signals.

So far, approaches to solving the problem have fallen short of ideal.

One approach is to settle for lower efficiency. Broadband antennas have worse efficiency than narrowband antennas for a given antenna size. But if lower efficiency is acceptable for a particular device design, a broadband antenna with sufficient band coverage will work. The trade-off is that the mobile device’s poor efficiency will mean less coverage area, more frequently dropped calls, lower data rate, and shorter battery life.

Another approach is to design an antenna with narrow instantaneous bandwidth, then tune within the antenna aperture to move the resonant frequency to the new band. This raises overall efficiency for the frequency range targeted by the design, but does not serve additional frequency bands.

Cavendish Kinetics takes a novel approach to the antenna problem that overcomes the limitations of either of these previous approaches.  Cavendish devices are small enough to be incorporated into the antenna aperture allowing narrow-instantaneous-bandwidth antennas to be tuned to different frequency bands.  The high performance of the devices allow wide-band antennas to be impedance matched, which allows the antenna to operate more efficiently in bands with poor performance.  Both design approaches can now be used.

 

High performance devices overcome design challenges:

  • High Quality (Q) factor across all frequencies. CK’s tunable capacitors have the highest usable Q factor in the industry – meaning the Q quoted in the specifications is delivered to the circuit on the board in practice, not just in theory.
  • Low parasitic capacitance. Due to the design and size of its devices, CK delivers the lowest Cmin in the industry, capable of 0.5pF and below. Low Cmin and high Q mean the upper frequency bands’ performance does not suffer from tuning the lower frequency bands.
  • Small volume. The small area and thickness of CK’s products mean that aperture tuning is possible without growing the size of the antenna structure. Many antennas are being constrained to 1 cubic centimeter or less, so space is at a premium. CK devices – at 2 mm2 and 0.4mm thick – allow for straightforward antenna structure integration.

To put CK’s antenna tuning achievements in perspective, a CK device behaves like a bank of 32 high-precision, high-Q capacitors using a 1P32T switch with zero insertion loss – and occupies less board space than two 0402 capacitors.