Overall Performance - dissappointing. The filters are off in frequency, so the unit has to be tuned to 6.3 GHz to peak the output. Even then, output power is a pitiful -17 dBm. The switch doesn't work at all.
Current draw-100 mA at 9.2 VC.
FILTER - the filter appears to be centered at 6.3 GHz, not 5.88 GHz as designed. This is a significant difference. Possible problem--dielectric undercutting from the milling process. I will have to adjust the filter passband in SuperStar and re-mill. The 4 GHz spur is 35 dB down, and others are not visible on the analyzer. The filter would have less loss with 3 poles rather than 4, and I think it could be optimized in SuperStar to have more stopband loss near the 4 GHz spur. A wider passband would allow more mechanical tolerance.
(10-16-1998 I know why the passband was shifted. The terminal impedance for an even-order filter is non-symmetrical. The input is 50 ohms, but the output is around 67 ohms. Coupled with the 50 ohm impedance of the MMIC input, this would have shifted the passband.)
VCO - SMV1960L appears to tune a much wider range than specified, as seen below. Fundamental frequencies are in parenthesis.
LOW: 5.7185 (1.9061) GHz
HIGH: 6.7504 (2.2501) GHz
SWITCH - I removed and jumpered C13. With J4 grounded, switching J3 has very little effect on the signal. Also, with J3 grounded, switching J4 between +5V and 0V has almost no effect. Replacing C13 increases the loss by about 3 dB and has otherwise no effect, so it appears the output of the VCO is indeed AC-coupled.
The problem must be the switch topology.
AMPS - Output is really small. Is this due to the skewed passband of the filter, or do I need more gain? Maybe an HP MMIC...
Description: Eliminated switch (for now). Lineup:
VCO->ERA-3->3POLEFILTER->ERA-3->ERA-5
Output: around -3 dBm. Not bad, but not enough for
a transmitter. Maybe one more amp stage. ERA-1's don't have
too much gain at 5.7 GHZ (around 10 dB), but ERA-3's and ERA-5's do....strange
that Mini-Circuits characterizes them as DC-3 and DC-6 GHz MMICs.
Maybe I could replace two ERA stages with one HP stage.
Filter: 3-pole filter doesn't have enough cutoff. We should go back to the 4-stage filter for next model, just try to widen it up a bit.
Maybe we could try one of the SSW-224 6 GHz switches in the next model...
Spurs: 3840 MHz: -42 dB 7680 MHz: -42 dB. Pretty nice!
I used the optimizing feature of the Eagleware SuperStar Pro simulator
to design the hairpin filter for this one. Here's a link to the circuit
file: 5el_1.ckt
Here's the theoretical S21 and S11 curves:.
Tuning it around, I think the shape is pretty close to theoretical.
This one's gonna fly!