HF Antenna Configuration

1. HF Antenna Configuration

2. HF Antenna Configuration • Background • HF tags were developed with particular applications in mind • Express parcels and packages • Airline baggage. • These applications had certain performance criteria • A reading zone 1m × 1m × 1m (approx 39” cubed) • Conveyor belts moving up to 3m/s (600 ft/sec) • Multiple tags in the field (around 5) • These criteria should be kept in mind when exploring more ambitious applications (greater reading distances/ more tags in the field)

3. HF Antenna Configuration • What if I want more than 1m range? • As a general rule, the larger the antenna loop, the longer the reading range. • A 1m × 1m Antenna can achieve up to 1m range • If the antenna gets much larger, the range drops again • These large antennas may exceed legal power limits. • Large antennas have a low field density and perform poorly when there are large numbers of tags in the field. • It is better to use opposing pairs of antennas • They can be driven from a single reader using a splitter • They can be optimised for tags parallel or at right angles to the antenna • They can be ‘rotated’ to read tags in more than one orientation

4. HF Antenna Configuration • What if I want to read lots of tags in the field? • As a general rule, the smaller the antenna loop, the better the ability to read closely packed tags • When tags are close together they • De-tune each other • Absorb more of the available RF energy • Smaller antennas can ‘illuminate’ tags that are closer together • If pairs of opposing antennas are to be used • Antennas on splitters develop a stronger field (Both driven) • Antennas that are ‘rotated’ have a weaker field (only one antenna is driven. • ‘Rotating field’ antennas should be closer together than those on a splitter • Another method is the alternately drive each antenna with a MUX

5. 2.00 1.90 1.80 1.70 1.60 1.50 H(x)r = 0.5 m 1.40 H(x)r = 0.4 m 1.30 H(x)r = 0.3 m 1.20 H(x)r = 0.2 m 1.10 H(x) [A/m] 1.00 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Metres HF Antenna Configuration • Magnetic Field Strength • Larger size antennas have lower field strengths close to the antenna, but read at longer distances. • Small antennas have high field strengths close to the antenna but the field quickly decays with distance.

6. 0.40 H(x)r = 0.5 m 0.30 H(x)r = 0.4 m H(x)r = 0.3 m H(x)r = 0.2 m 0.20 H(x) [A/m] 152 dBµV/m 93 mA/m 0.10 (100 mA/m) 0.00 0.6 1.0 0.5 0.7 0.8 0.9 Metres HF Antenna Configuration • Magnetic Field Strength • The activation field strength for Tag-it HF-I inlays is 93 mA/m

7. HF Antenna Configuration • Reading close packed tags (1) • The Antenna below was designed to create a strong field to read boxes of optical lenses. • It uses parallel loops to ensure each tag is near to an antenna • This is an straight-forward application – the tags are all in the same orientation Box of Lenses

8. HF Antenna Configuration • The 72 tags are only a few mm apart and can be in any vertical orientation • The two crossed antennas are multiplexed • Reading close packed tags (2) • The Tube reader below uses small antennas to maximize the field strength

9. HF Antenna Configuration • Antenna Field Lines • With a pair of antennas on a splitter, the field patterns depend on the phase. In-Phase Antennas Out-of-Phase Antennas

10. SPLITTER HF Antenna Configuration • Using Splitters (1) • If antennas need to be used facing each other, I.e. across a conveyor system, they can be used with a 0º two way splitter to more than double the range. • Although a splitter adds losses, when antennas are used opposing each other, with careful tuning good performance results. • It is important though, to ensure that the antennas are in phase in we need to optimize for Tags passing parallel to the antennas.

11. SPLITTER HF Antenna Configuration • Using Splitters (2) • If antennas need to be used facing each other, I.e. across a conveyor system, but the tag orientation is not optimal, use a 90º two-way splitter to ensure that the antennas are exactly 90º Out-of-Phase. • The same effect can be achieved using a ¼ wavelength of extra feeder cable to one antenna

12. Rx only Tx and Rx HF Antenna Configuration • What if the tags can be in any orientation? • If the tags can pass through a system in any orientation, then multiple antennas have to be used. • We can create a ‘Rotating field’ effect by having a ‘Basic’ antenna that serves both transmit and receive functions (Tx/Rx) and opposing it, a ‘Complementary’ antenna that is receive only (Rx) • By careful adjustment of the Complementary antenna we can get the RF field to rapidly oscillate between In-Phase and Out-of-Phase thus reading Tags in both orientations

13. HF Antenna Configuration • Complementary Antennas • A pair of rotating antennas will detects all tags in vertical orientations and some tags in high and low horizontal positions as they pass through. • Unfortunately, there is ALWAYS a reading hole at the centre for horizontal tags.

14. Complementary (RX) Basic (TX/RX) HF Antenna Configuration • Removing the Reading Hole • The reading hole can be removed with a second set of antennas • The second set are connected to the same reader using two splitters • The overlap removes the hole • The reader power output will need to be increased to compensate for losses in the splitters

15. Complementary (RX) Basic (TX/RX) HF Antenna Configuration • Removing the reading Hole (2) • The reading hole can also be removed with an extra horizontal antenna either above or below. • The antenna MUST be outside the zone of the Basic/ Complementary pair • This antenna is on a splitter with the Basic (RX/TX) antenna

16. HF Antenna Configuration • What if I need the portal to be more compact? • One approach is to use three antennas and read each one in turn using a multiplexer. This was the basis of the British Airways tunnel reader and other portals in commercial use

17. HF Antenna Configuration • Three antennas cover the three tag orientations

18. HF Antenna Configuration • Three antennas in position

19. HF Antenna Configuration • London Heathrow System

20. HF Antenna Configuration • London Heathrow System Antennas

21. HF Antenna Configuration • If we were to build another!