1 / 11

Saltdome Shower Array: Antennas & Antenna Modeling

Saltdome Shower Array: Antennas & Antenna Modeling. Peter Gorham University of Hawaii at Manoa. SalSA antenna requirements. Must fit down a borehole, between 2 and at most 4.5 to 5” diameter Must pass tension member through its center (clamp on or integral)

anthea
Download Presentation

Saltdome Shower Array: Antennas & Antenna Modeling

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Saltdome Shower Array: Antennas & Antenna Modeling Peter Gorham University of Hawaii at Manoa P. Gorham, SLAC SalSA workshop

  2. SalSA antenna requirements • Must fit down a borehole, between 2 and at most 4.5 to 5” diameter • Must pass tension member through its center (clamp on or integral) • Dual polarization a high priority (linear polarizations seem like the best bet for bandwidth) • Should be fully compensated for lithostatic pressure • Wide bandwidth: 100% or more single-mode if possible • Easy to make, low cost, no integral electronics P. Gorham, SLAC SalSA workshop

  3. Antenna test & modeling • UH SalSA group has dedicated anechoic chamber 14’ by 10’ by 24’, good 100-20,000 MHz • Foundation slab can support large salt stack for embedded antenna tests • Test equipment: time domain response to ~10ps; spectral analysis to 20 GHz • Antenna modeling: • NEC2, NEC2_salt (embedded dieletric version): Beam patterns, impedance • XFDTD (commercial package): time domain response P. Gorham, SLAC SalSA workshop

  4. Dual polarization Antenna studies • Vertical polarization is easy • “Fat” dipoles are excellent for this • Horizontal polarization is tough in a narrow borehole • Use complementary slot antenna, but matching the vertical is difficult • Best solution: probably adjacent (but separate) antennas Test data P. Gorham, SLAC SalSA workshop

  5. Fat dipole results in salt 120 MHz 180 MHz Gain, dB • 4” diameter by 30 inch length, copper • Usable from 50MHz to 1 GHz (better than model predicts) • Single mode from 50-350MHz 50 ohm feedpoint coupling 530 MHz 370 MHz SWR (predicted) SWR (measured) Frequency, Hz/MHz P. Gorham, SLAC SalSA workshop

  6. Finite difference time domain, slot-cylinder reference antenna with parameters: • cylinder length = 81.5 cm • cylinder radius = 5.1 cm • slot width = 30 mm • slot length = 68 cm • placed in air space without HDPE P. Gorham, SLAC SalSA workshop

  7. Slot-cylinder in salt and air • Dramatic effects when immersed in salt, but surprisingly, HDPE core gives best bandwidth P. Gorham, SLAC SalSA workshop

  8. More slot-cylinder in salt • 50 ohms impedance match in salt is tolerable, probably even better with HDPE core. P. Gorham, SLAC SalSA workshop

  9. Slot-cylinder Antennas • Best response at feedpoint impedance of about 150 to 200 ohms, need 3:1 or 4:1 transformer balun • Antenna model shows good efficiency from 175 MHz up to more than 700 MHz • But: very sensitive to diameter--this assumes about a 4 inch borehole or more P. Gorham, SLAC SalSA workshop

  10. Slot-cylinder predicted beam patterns 180 MHz 210 MHz 280 MHz • Antenna is single-mode from 180-280MHz, goes multi-mode after that • 2-3dB of front-to-back asymmetry favoring the side with slot antenna 330 MHz P. Gorham, SLAC SalSA workshop

  11. Summary • 4 inch diameter dipole and slot-cylinder antennas look good • Dipole ~80cm high, good Vpol single-mode response from <100-350MHz • Slot-cylinder of order same length will get good 180-300 MHz Hpol single-mode, but with ~few dB front-to-back directionality • Polarization separation for both is outstanding (-20dB cross-pol at all angles) • Helical antennas investigated but do not provide clean polarization separation • Become elliptically polarized at off-principal axes • Bandwidths relatively narrow • Combination of fat dipoles and slot-cylinders seems a viable configuration for SalSA P. Gorham, SLAC SalSA workshop

More Related