Thanks for sharing your thoughts on the phased array approach.
I especially appreciated your block diagrams which really helped. I'm
sorting through the approach and will likely have some questions.
Regarding amplifiers for 5.7 GHz, Sirenza has a 1/4 watt for $4.80. It
draws 165mA @ 5V or 7 amps for 43 of them.
Now here's the real heartburn device. The Hittite HMC409LP4 (I think the
one you referred to) provides just over 1 watt, costs $8.52 (not bad at
all) but runs 615mA at 5V - or 26 Amps for 43 antennas. If that input
power doesn't bother anyone - there's part of our design!
I've never heard any estimates of what DC power Eagle is planning to
deliver. Is that figure available yet?
Thanks again Tom for your time and thoughts.
> central feed-point impedance was high (several kohms, as compared with
> the 450 ohm open wire t-line. The T-line was marked off in 0.1
> wavelength units; since the elements were spaced a half-wave, every
> 5th mark was at an antenna pole. To phase the array to a given
> declination might have required (as an example) a phase increment of
> 0.15 wavelengths. The first element was tapped onto the line at
> position 0. the second (a half wave away) was at position 0.515 but
> with the connection block flipped to get a 180° phase reversal. then
> the 3rd element should have been at 1.30 with no reversal, but it was
> closer to tap at 0.80 with a reversal. And so forth thru all 64
> elements. It took about an hour to go thru the array to re-phase it
> for a different declination. Because the taps ended up contributing a
> (nearly) randomized set of reflections, the inter-element interactions
> were quite small unless the array was phased to the zenith (when all
> the individual ~1.1:1 VSWR phasors added up).
> Thinking back on these sins of my youth, I came up with a new idea
> based on points 7 & 9, which is seen in the first attached drawing
> "tapped delay line".
> As a variation on Franklin's idea #7, my thoughts are to use the Nth
> sub-harmonic of the carrier. We might make N=8 so that we distribute
> 730 MHz (corresponding to 5840 MHz center downlink); at this
> frequency, one wavelength ~ 411 mm. For a 7-element array, I show a
> 6*L piece of coax, with taps uniformly space L and terminated in its
> characteristic impedance. There a 7 uniformly tapped steps and at each
> tap is a high impedance buffer amplifier (think coax Ethernet here).
> The buffer feeds a *N multiplier (I suggested N-8 because Hittite has
> some really nice active microwave doublers); alternatively, it could
> involve a PLL, perhaps with a DRO "puck" as the resonator. The
> microwave signal from the multiplier feeds a double-balanced mixer to
> generate BPSK, followed by a PA and the patch antenna element. Note
> that the BPSK modulation could be done at a lower frequency inside the
> multiplier, in which case the modulation phase shift is < 180° by some
> integer divisor.
> However, at this point we have not phased the array -- the
> interelement phase is determined by the tap interval L and the
> frequency f/N. If we could make the tapped delay line from rubber,
> then we could get an incremental change in the phase by simply
> mechanically stretching it. Since we can't change the physical length,
> can we tune the delay line electronically? I think that the scheme
> shown in the 2nd "rubber" drawing will work. At each tap point, we add
> a varactor and set the bias on all the varactors with a D/A. As we
> change the voltage across the diode string, each diode's capacity will
> be changed by the same amount, making the equivalent of
> computer-controlled "rubber". Voila -- we can generate the smooth
> phase gradient needed to point the antenna.
> Note that the phase "swings" from the end where the f/N oscillator
> injects its signal. But IMHO, we want to "lock" the phase of the
> central element, half-way down the tapped line. I suggest that, in
> addition to programming the DC voltage necessary to point the antenna,
> the computer adds a "DC" constant to each string based on keeping the
> central element as the phase reference. Note that some of the delay
> line taps will not have an PA/antenna element attached to it; the
> degenerate case is the central element which can only be physically
> present in one of the intersecting arms.
> The antenna geometry I tend to favor is the 43-element "12-spoke"
> ("/two bits/" * 43 = $10.75) version which has 3 9-element arms (with
> a single common central element) and 3 6-element arms (with the
> central 3 elements missing). All 6 would use an 8*L delay line, with
> the central phase of 5 of the lines slaved to the 6th.
> As usual, please enter into a lively, feedback-provoking discussion --