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2011 S DARN W kh 2011 SuperDARN Workshop 2011 SuperDARN Workshop 2011 SuperDARN Workshop D t th C ll N H hi USA Dartmouth College, New Hampshire, USA Dartmouth College, New Hampshire, USA May 30 June 3 May 30 - June 3 FPGA b d C bl L th Ph M t hi FPGA-based Cable Length Phase Matching FPGA-based Cable Length Phase Matching FPGA based Cable Length Phase Matching Bienvenu B Ngoc V Custovic E Whittington J Elton D & Devlin J Bienvenu, B., Ngoc, V., Custovic, E., Whittington, J., Elton, D., & Devlin. J. Bienvenu, B., Ngoc, V., Custovic, E., Whittington, J., Elton, D., & Devlin. J. Department of Electronic Engineering Department of Electronic Engineering At C bl l th ( ) L (dB) Δ L (dB) Antenna Cable length (m) Loss (dB) Δ Loss (dB) SuperDARN radars using a time delay phasing matrix such as the existing Including the cable length adjustment is simply a matter of measuring and 89 35 0 23 0 66 SuperDARN radars using a time delay phasing matrix, such as, the existing Including the cable length adjustment, is simply a matter of measuring and 8, 9 35 0.23 0.66 TIGER Bruny Island and Unwin systems, require equal length antenna storing the various cable length differences as site constants then 7 10 49 0 33 0 56 TIGER Bruny Island and Unwin systems, require equal length antenna f d bl th t h i f b f i i t di t bd Th bl storing the various cable length differences, as site constants, then 7, 10 49 0.33 0.56 feeder cables so that phasing for beam forming is not disturbed. The cable calculating appropriate phase offsets for each transceiver for the frequency 6 11 63 0 42 0 47 length used for all antennas is dictated by the longest span i e distance to calculating appropriate phase offsets for each transceiver for the frequency 6, 11 63 0.42 0.47 length used for all antennas is dictated by the longest span, i.e. distance to to be transmitted. As shown in figure 3, these values are simply loaded into 12 0 2 0 38 the furthest antenna from the equipment hut This results in significant to be transmitted. As shown in figure 3, these values are simply loaded into th DDS l ith th h ti d b f i h 5, 12 77 0.52 0.38 the furthest antenna from the equipment hut. This results in significant the DDSs, along with the phase compensation and beam forming phase additional cable (up to ~100m) for antennas located closer to the hut values prior to the start of each pulse sequence 4, 13 91 0.61 0.28 additional cable (up to ~100m) for antennas located closer to the hut. values prior to the start of each pulse sequence. 4, 13 91 0.61 0.28 Typically this excess cable is coiled up inside the hut or in an auxiliary shed 3, 14 105 0.70 0.19 Typically this excess cable is coiled up inside the hut or in an auxiliary shed h h 3, 14 105 0.70 0.19 next to the hut. 2, 15 119 0.80 0.09 next to the hut. 2, 15 119 0.80 0.09 1 16 133 0 89 0 00 With the FPGA based transceivers in the new TIGER 3 (Buckland Park) 1, 16 133 0.89 0.00 With the FPGA-based transceivers in the new TIGER-3 (Buckland Park) rear 18 19 105 0 70 0 19 radar phasing is performed as part of the Direct Digital Synthesis (DDS) rear 18, 19 105 0.70 0.19 radar, phasing is performed as part of the Direct Digital Synthesis (DDS) rear 17 20 119 0 80 0 09 generation of the carrier wave Furthermore as this system has one rear 17, 20 119 0.80 0.09 generation of the carrier wave. Furthermore, as this system has one transceiver per antenna individual phase settings can be maintained for (i) Table 1: TIGER 3 cable lengths with cable loss @ 10MHz transceiver per antenna individual phase settings can be maintained for (i) b f i (ii) ti f h i ti i t it d i th beam forming; (ii) correction of phase variation in transmit and receive paths; The Loss value is the change in loss with respect to the longest cable in the beam forming; (ii) correction of phase variation in transmit and receive paths; d (iii) ti f diff i t f d bl l th I thi The Loss value is the change in loss with respect to the longest cable in the and (iii) compensation of differences in antenna feed cable length. In this system and represents the signal improvement at the corresponding system the initial phase offset for the DDS (in each transceiver) at the start system and represents the signal improvement at the corresponding system the initial phase offset for the DDS (in each transceiver) at the start Figure 3. TIGER-3 DDS Carrier wave generation with individual phase offset entry transceiver resulting from the use of minimum length cables This has also of each pulse sequence is just the sum of these phase values transceiver resulting from the use of minimum length cables. This has also $ $ of each pulse sequence, is just the sum of these phase values. resulted in a cost saving of more than $4000 (~850m @ $5/m) resulted in a cost saving of more than $4000 ( 850m @ $5/m). This feature enables cable lengths in the TIGER-3 radar to be set to a Whil th til b fit it i i t t t t th t th i bl bl This feature enables cable lengths in the TIGER 3 radar to be set to a h i l ii i 800 f bl Th i b fit f thi While there are certainly benefits, it is important to note that the variable cable physical minimum, saving over 800m of cable. The main benefits of this are: lengths have negligible effect on the beam width In a worst case scenario The following tests conducted on the bench using (a) a cabling cost sa ing and (b) a s stem ide increase in transmit and lengths have negligible effect on the beam width. In a worst case scenario, The following tests, conducted on the bench using (a) a cabling cost saving; and (b) a system wide increase in transmit and there would need to be a 10% power output variation across the array to TIGER-3 transceivers illustrate the effects of receive power Additional benefits are a slightly easier implementation as there would need to be a 10% power output variation across the array to o TIGER 3 transceivers, illustrate the effects of receive power . Additional benefits are a slightly easier implementation, as produce 0 1 o beam spreading This was calculated by altering power outputs phase calibration and cable length compensation there are no longer any cable coils and elimination of any possible produce 0.1 beam spreading. This was calculated by altering power outputs phase calibration and cable length compensation i ti Th t i fi d t there are no longer any cable coils and elimination of any possible on each antenna using the EZNEC antenna modeling package. in operation. The transceivers were configured to temperature variation effects acting on the cable coils The only downside is on each antenna using the EZNEC antenna modeling package. be connected to antennas #9 (yellow trace in the temperature variation effects acting on the cable coils. The only downside is il f li h b di h h l l d h hi be connected to antennas #9 (yellow trace in the a potential for slight beam spreading, however we have calculated that this Figure 4. DAC out, no comp following plots) #10 (blue) and #12 (purple) the a potential for slight beam spreading, however we have calculated that this ill b l th 0 1 o following plots), #10 (blue) and #12 (purple), the will be less than 0.1 . transmit frequency was set to 8MHz and to simplify transmit frequency was set to 8MHz and to simplify Th TIGER 3 d t i i di id l t it d i th results no beam phasing was used (i e set up to The TIGER-3 radar transceivers possess individual transmit and receive path results, no beam phasing was used (i.e. set up to t it d th b it ) T CRO th calibration and compensation Before a given frequency is transmitted a short transmit down the bore site). Two CROs were then calibration and compensation. Before a given frequency is transmitted a short transmit down the bore site). Two CROs were then t t it th DAC t t (i th t it calibration cycle can be run to measure the phase delay through both the set up to monitor the DAC output (in the transmit calibration cycle can be run to measure the phase delay through both the Figure 5 Ant out no comp path) and the Antenna output of each transceiver transmit and receive paths Once measured the phase delay can be simply The TIGER-3 radar is being constructed with a 14m antenna spacing 80m Figure 5. Ant out, no comp path) and the Antenna output of each transceiver . transmit and receive paths. Once measured, the phase delay can be simply The TIGER-3 radar is being constructed with a 14m antenna spacing, 80m compensated for by loading a negative phase offset value into the appropriate between the Main and Auxiliary arrays and with the equipment hut located compensated for by loading a negative phase offset value into the appropriate DDS i t th t t f l A i lifi d bl k di f th between the Main and Auxiliary arrays, and with the equipment hut located b h 20 b hi d h Mi Mi i l l h ‘S i Initially no compensation is used thus while the DDS prior to the start of a pulse sequence. A simplified block diagram of the between the arrays, 20m behind the Main array . Minimal length ‘Spinner Initially, no compensation is used, thus, while the DDS prior to the start of a pulse sequence. A simplified block diagram of the TIGER 3 t it d i th hi hli hti th h t between the arrays, 20m behind the Main array . Minimal length Spinner f t d’ ½” lid f d ith i l l f 0 67dB/100 @ DAC outputs Figure 4 are in phase the Antenna TIGER-3 transmit and receive paths, highlighting the phase measurement manufactured’ ½” solid feeder coax, with a nominal loss of 0.67dB/100m @ DAC outputs, Figure 4, are in phase, the Antenna t t Fi 5 t f h d t diff i blocks is shown in figure 2 10MHz is used to connect each transceiver box to its associated antenna outputs, Figure 5, are out of phase due to differing blocks, is shown in figure 2. 10MHz, is used to connect each transceiver box to its associated antenna. Fi 6 At t h outputs, Figure 5, are out of phase due to differing h dl i th t it th f th th Cable lengths and corresponding losses are shown in table 1 Figure 6. Ant out, phase comp phase delays in the transmit paths of the three Cable lengths and corresponding losses are shown in table 1. transceivers This is corrected by applying phase transceivers. This is corrected by applying phase calibration and compensation Figure 6 resulting in calibration and compensation, Figure 6, resulting in Antenna outputs that are now in phase Finally Antenna outputs that are now in phase. Finally, cable length compensation is applied, Figure 7, so cable length compensation is applied, Figure 7, so th t t t i l ill b i h t th d f that output signals will be in phase at the end of Figure 7. Ant out, phase & length comp cables of length 35m 49m and 77m respectively Figure 7. Ant out, phase & length comp cables of length 35m, 49m and 77m respectively . FPGA-based cable length compensation has been FPGA based cable length compensation has been G 3 f developed in TIGER-3 transceivers to allow for developed in TIGER 3 transceivers to allow for ii l l th t f d bl Thi lt minimal length antenna feeder cable. This results in a modest cost saving and reduction in cable in a modest cost saving and reduction in cable losses While there will be slight beam spreading it losses. While there will be slight beam spreading, it Figure 2: Simplified block diagram of TIGER-3 transmit and receive paths will be less than 0 1 o Figure 2: Simplified block diagram of TIGER-3 transmit and receive paths, with phase calibration measurement highlighted in yellow Figure 1: Main & auxiliary arrays showing minimum length cable runs will be less than 0.1 . with phase calibration measurement highlighted in yellow Figure 1: Main & auxiliary arrays showing minimum length cable runs
