A historical end-fire 34-slot travelling wave rectangular waveguide antenna has a more rigid structure than comparable travelling or leaky-wave end fire antennas. In simulation the published antenna design had peak directivity of 16.2dBi with 1dB directivity bandwidth of 12.2% but the matching was poor with S11≈-3dB. The feed section of the antenna was found to be independent of the travelling wave and front sections, enabling faster tuning. Changing the original narrow wall inclined slot feed to a narrow wall Z-slot gave S11≤-10dB bandwidth of 8% making the antenna of practical value. Comparison is made to a dielectric polyrod antenna which had comparable performance across an octave

Gray, Derek

Le Kernec, Julien

Mousavi, Pedram

Enlighten

   Re-examination of Watson’s microwave Yagi aerial  Derek GRAY†,  Pedram MOUSAVI (posthumous)‡ and Julien Le KERNEC† †James Watt School of Engineering,  University of Glasgow,  Glasgow,  UK. ‡Intelligent Wireless Technology Laboratory,  University of Alberta,  Edmonton,  Canada. E-mail:  †(Derek.Gray,  Julien.LeKernec) @glasgow.ac.uk  Abstract  A historical end-fire 34-slot travelling wave rectangular waveguide antenna has a more rigid structure than comparable travelling or leaky-wave end fire antennas.  In simulation the published antenna design had peak directivity of 16.2dBi with 1dB directivity bandwidth of 12.2% but the matching was poor with S11≈-3dB.  The feed section of the antenna was found to be independent of the travelling wave and front sections,  enabling faster tuning.  Changing the original narrow wall inclined slot feed to a narrow wall Z-slot gave S11≤-10dB bandwidth of 8% making the antenna of practical value.  Comparison is made to a dielectric polyrod antenna which had comparable performance across an octave.  Key words  polyrod antenna,  travelling wave antenna.  1. Introduction Between 1942 and 1944 fundamental work to develop shunt and series rectangular waveguide fed slot radiators at 2.8 and 9.375GHz was undertaken by W.H. Watson and E.W. Guptill at McGill University [1].  The majority of that work was on broadside or near broadside radiating standing wave and travelling wave waveguide antennas which are widely used today at X-band and higher showing the significant advance that that work was over prior work on coaxial cable fed dipole arrays for high power handling capability,  low internal losses and structural strength.  In contrast,  the single end fire WR-90 antenna briefly described at the end of [1] has apparently been forgotten,  not appearing in any subsequent open or restricted literature.  If built from WR-90 or some other rectangular metal tube it would be more robust than the printed Yagi’s developed for a 30GHz wireless office system [2-5] and dielectric antennas [6-8],  and further could enclose a T/R module and thus protect it from physical abuse and ionizing radiation.  Conversely,  if built from metallized foam this antenna would be loss mass and have more degrees of freedom than a polyrod antenna.  These potential advantages were motivation for building a copy and then undertaking a simulation study [9].  Those results are re-analyzed here,  the modular nature of the antenna was investigated and an alternate feed section presented.  Figure 1:  Photograph of a copy of Watson’s Yagi antenna with 10-slot antenna for scale comparison.  2. Watson’s microwave Yagi aerial Here the S11 and directivity of a “free floating” polyrod antenna were taken as the baseline as it was a near ideal endfire antenna when fitted with an optimized cup reflector,  Figure 2 [10, 11].  As Watson’s Yagi did not have such an additional external reflector,  it is fair to make comparison to the polyrod stripped of its.  With a 45mm long feed section of cross-linked polystyrene filled - 16 -IEICE Technical Report A･P2023-4(2023-04)信学技報一般社団法人　電子情報通信学会THE INSTITUTE OF ELECTRONICS, INFORMATION AND COMMUNICATION ENGINEERSThis article is a technical report without peer review, and its polished and/or extended version may be published elsewhere. 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　             Copyright ©2023 by IEICE  16mm diameter circular waveguide,  the total length of the FEKO™ polyrod antenna model was 460mm,  Figure 2.  In contrast,  the FEKO™ model of Watson’s Yagi from Figure 58 of [1] was 382mm.  It is acknowledged that been 2.5λ0 shorter at 9.375GHz makes any direct comparison of these endfire antennas unfair but want to qualify the behavior of the antenna as originally published before undertaking any new design work.  Figure 2:  Watson’s Yagi antenna compared to the optimized polyrod antenna from [11]. Full dimensioning for Watson’s Yagi are given in Figure 58 of [1] and Figure 2 of [9].  The antenna consisted of 2 sets of 17 slots cut into the narrow walls of a section of WR-90 waveguide which terminated in a wedge and an internal shorting block just above the inclined radiating slots.  All slots were 1.6mm wide.  Sixteen of the 17 slots were transverse (not inclined) so did not couple to the dominant mode within the waveguide but did couple to the Transverse Magnetic (TM) surface wave on the outside of the waveguide.  This makes the E-plane normal to the slotted narrow wall of the WR-90 rectangular waveguide,  so the E-plane (φ=0°) of the antenna is in the plane of the page in Figure 2,  making the H-plane (φ=90°) out of the page.  Figure 3:  Simulated and measured performance of Watson’s Yagi antenna. Both the measured and simulated S11≤-3dB around 9.375GHz,  Figure 3.  This poor matching likely explains the non-publication beyond the diagram in Figure 58 of [1].  The resonance shift from 9.3GHz to 9.6GHz is speculated to be caused by a combination of minor manufacturing errors and interaction with the flange,  which was not included in the FEKO™ model.  In contrast,  the peak directivity results were impressive for a relatively short antenna with 16.2dBi at 9.3GHz.  Figure 4:  Simulated 9.375GHz radiation patterns of Watson’s Yagi antenna,  from FEKO™. At 9.375GHz,  Watson’s Yagi produced a clean endfire radiation pattern,  Figure 4.  The E-plane 3dB beamwidth was narrower than that of the polyrod,  while the H-plane was broader,  Figure 4 and 5.  Also in line with prior general analysis of endfire antennas [12],  in opposition to the 3dB beamwidths,  the E-plane first sidelobe levels were higher than those of the H-plane,  100mmpolyrod with cuppolyrodWatson’s YagifeednosewedgeTM guiding section8 8.5 9 9.5 10 10.5 11-505101520Frequency (GHz)S11 & Directivity (dB)S11 exptS11 FEKODir FEKO-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180-20-15-10-5051015Angle (°)Directivity (dBi)φ=0° Eθφ=0° Eφφ=90° Eθφ=90° Eφ- 17 -  Figures 4 and 6.  Figure 5:  Simulated 3dB beamwidth of Watson’s Yagi antenna,  from FEKO™.   Figure 6:  Simulated sidelobe level of Watson’s Yagi antenna,  from FEKO™.  3. Coupling tests of travelling wave slotted section Having described the basic behavior of Watson’s Yagi,  the transverse slot travelling wave section was analyzed to see whether it constrained the directivity bandwidth of the antenna.  A simple monopole coupling model along a short section of WR-90 waveguide was simulated in FEKO™,  Figures 7 and 8.  Adding 10 slots copied from Watson’s Yagi between the monopoles increased the S21 from -22dB to -16dB at 9.375GHz,  showing the ability of the slots to modify the near field of a monopole and to channel the TM wave along the narrow wall to be received by the second monopole.  Figure 7:  Annotated CAD of monopoles on WR-90 waveguide to test 10 transverse slots,  from FEKO™.    Figure 8:  Simulated S-parameters of monopoles on WR90 waveguide section,  from FEKO™. Normalizing the peak directivity of Watson’s Yagi and the S21 of the monopole coupling model enabled a direct comparison,  Figure 9.  There was not a straight mapping of the S21 to the antenna’s peak directivity characteristic,  suggesting that the transverse slot travelling wave section contributed to the behavior of the antenna along with some other factors possibly stemming from the poor S11 of the feed section. 8 8.5 9 9.5 10 10.5 111520253035Frequency (GHz)3dB beamwidth ( °)Watson E-planeWatson H-plane4-slot E-plane4-slot H-planepolyrod E-planepolyrod H-plane8 8.5 9 9.5 10 10.5 11-18-16-14-12-10-8-6-4-20Frequency (GHz)1st  SLL (dB)Watson E-planeWatson H-plane4-slot E-plane4-slot H-planepolyrod E-planepolyrod H-plane8 8.5 9 9.5 10 10.5 11-30-25-20-15-10-50Frequency (GHz)S parameter (dB)S11 no slotsS21 no slotsS11 slotsS21 slots- 18 -   Figure 9:  Comparison of monopole on WR-90 coupling and directivity of Watson’s Yagi antenna,  from FEKO™. Changing to aluminum or carbon fiber reinforced plastic (CFRP) tube would decrease the mass of the antenna without compromising the structural strength.  A readily available near WR-90 sized 6063 alloy aluminum tubing has internal dimensions of 22.6x9.6mm and 1.2mm wall thickness and cutoff frequency of 6.63GHz,  as compared to 6.56GHz for WR-90.  Four different combinations for slot cut depth and spacing were trialed to investigate the effect upon the passband,  Table 1.  The monopole coupling model of Figure 7 was resized to the 6063 tubing dimensions and rerun in FEKO™ for each pair of slot cut depth and slot spacing. TABLE 1: Slot dimensions. Name Cut depth (mm) Spacing (mm) Watson’s Yagi 2.0 9.92 #1 3.09 12.95 #2 2.73 11.27 #3 2.60 10.08 #4 2.35 9.65 All 4 slot arrangements introduced resonances to the transmitting monopole S11,  Figure 10.  #1 caused the greatest disturbance as its pass-band stopped at 9GHz as seen in the S21,  Figure 11.  #4 caused the least disturbance having its pass-band stop at 10.5GHz,  thus been comparable to Watson’s design.  All slot arrangements increased the maximum S21 by 5dB as seen with the test of Watson’s design.  Figure 10:  Simulated S11 of monopoles on 6063 aluminum tubing section,  from FEKO™.   Figure 11:  Simulated S21 of monopoles on 6063 aluminum tubing section,  from FEKO™.  4. Aluminum antenna feeds Having found that the transverse slot travelling section worked as well as possible,  the feed section of Watson’s Yagi was thus the sole cause of the poor matching.  Having a single radiating slot in either narrow wall limited the bandwidth,  and ideally the corners of the waveguide rectangular tube would not the cut so as to preserve structural strength.  I or Z-slots fitting entirely within the narrow walls of rectangular waveguide have been used in arrays in the past [13, 14].  Initially different combinations of 3 Z-slots and U-slots were tried on a 382mm long antenna without the transverse slot travelling wave section to develop a well matched and 8 8.5 9 9.5 10 10.5 11-25-20-15-10-50Frequency (GHz)Normalised S21/Directivity (dB)S21Dir8 8.5 9 9.5 10 10.5 11-20-18-16-14-12-10-8-6-4-20Frequency (GHz)S11 (dB)no slots#1#2#3#48 8.5 9 9.5 10 10.5 11-50-45-40-35-30-25-20-15-10Frequency (GHz)S21 (dB)no slots#1#2#3#4- 19 -  directional feed at 9.375GHz.  Later,  different combinations of 4 slots were trialed.  Both 3 and 4 slot narrow band matched feeds were developed and the better examples are given in Figure 12.  Figure 12:  Annotated diagrams of 3 and 4 slot feeds. All 4 transverse slot travelling wave arrangements from Table 1 were tried as a set of 14 slots started 8.8mm above the last feed slot.  As with the monopole coupling model,  #1 slot arrangement caused the greatest disturbance to the S11 of the 3 and 4 slot fed antennas,  while #4 the least,  Figures 13 and 14.  Figure 13:  Simulated S11 of 3-slot feeds and 14 slot antennas and baseline polyrod;  from FEKO™. Slot arrangement #4 gave the widest directivity bandwidth for both 3 and 4-slot feeds,  Figures 15 and 16.  The highest directivity was 15.2dBi at 9.5GHz from the 4-slot fed antenna,  Figure 16.  This was 1dB lower than from Watson’s Yagi.  There was more radiation around θ=90° than in the E-plane pattern of Watson’s Yagi accounting for the lower directivity,  Figures 17 and 18.  Figure 14:  Simulated S11 of 4 slot feeds and 14 slot antennas and baseline polyrod;  from FEKO™.   Figure 15:  Simulated directivity of 3-slot feeds and 14 slot antennas and baseline polyrod;  from FEKO™.   Figure 16:  Simulated directivity of 4-slot feeds and 14 slot antennas and baseline polyrod;  from FEKO™. 8 8.5 9 9.5 10 10.5 11-25-20-15-10-50Frequency (GHz)S11 (dB)feed#1#2#3#4polyrod8 8.5 9 9.5 10 10.5 11-25-20-15-10-50Frequency (GHz)S11 (dB)feed#1#2#3#4polyrod8 8.5 9 9.5 10 10.5 11-15-10-505101520Frequency (GHz)Directivity (dBi)feed#1#2#3#4polyrod8 8.5 9 9.5 10 10.5 11-15-10-505101520Frequency (GHz)Directivity (dBi)feed#1#2#3#4polyrod- 20 -    Figure 17:  Simulated 9.375GHz radiation pattern of 3-slot antenna,  from FEKO™.  Figure 18:  Simulated 9.375GHz radiation pattern of 4-slot antenna;  from FEKO™.  5. Conclusions and future work A historical “lost” endfire waveguide antenna was rebuilt and analyzed in FEKO™.  The directivity performance was found to be quiet good for an antenna about 2λ0 shorter than optimal endfire length.  However,  the matching was poor explaining this antenna type’s disappearance from the literature.  The original travelling wave transverse slot design was found to be optimal,  and a derivative worked well with 2 different new well matched feed sections.  Future work will consider decreasing E-plane θ=90° radiation from the feeds,  widening the bandwidth of those and increasing the antenna length. Acknowledgement Dr. P. Mousavi,  his wife Dr. M. Deneshmand and their two children were murdered along with 172 other souls on January 8th,  2020 when Ukraine International Airlines Flight PS752 was shot down leaving Imam Khomeini International Airport.  Our two friends and their children are greatly missed. 8. References [1] W.H. Watson,  “Resonant slots,”  J. of the IEE,  pt. IIIA: Radiolocation,  vol. 93,  iss. 4,  1946,  pp. 747 – 777. [2] L. Shafai,  “A microstrip line-fed leaky wave antenna for EHF links,”  8th Int. Conf. Wireless Communications Wireless’96, Calgary,  8–10 July 1996,  pp. 222-228. [3] J.S. Wight,  M.G. Stubbs & L. Shafai,  “EHF system architectures for broadband indoor wireless LAN and LMCS applications,” Symposium on Antenna Technology and Applied Electromagnetics, Montreal, QC, Canada, 06-09 August 1996. [4] M.G. Stubbs,  C. Glaser,  H. Do Ky,  C.J. Verver,  L. Shafai & J.S. Wight,  “Development of a 30 GHz, wireless LAN transmit/receive module,”  27th European Microwave Conference,  Jerusalem, Israel, 1997. [5] L. Shafai,  “Microstrip line fed microstrip end-fire antenna,”  United States patent number 5,896,108,  granted April 20th,  1999. [6] G.C. Southworth,  Principals and applications of waveguide transmission,  D. van Nostrand Company,  Inc.,  Princeton,  NJ,  1950. [7] Y. Shiau,  “Dielectric rod antennas for millimeter-wave integrated circuits,”  IEEE Trans. Microw. Theory Tech.,  Nov. 1976,  pp. 869-872. [8] S. Kobayashi,  R. Lampe,  N. Deo and R. Mittra,  “Dielectric antennas for millimeter-wave applications,”  IEEE Int. Microwave Symp.,  1979,  pp. 566 - 568. [9] D. Gray,  “Examination of Watson’s microwave Yagi aerial,”  3rd Asia-Pacific Conference on Antennas and Propagation (APCAP 2014),  Harbin,  July 2014. [10] K. Sato,  I. Oshima & H. Nakano,  “Rod antenna for 28-GHz band operation,”  IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications,  2022. [11] D. Gray,  J. Le Kernec & K. Kontis,  “Integrated transition with dielectric rod for vacuum chamber,”  IEICE Tech. Rep.,  Hiroshima Institute of Technology,  vol. 122,  no. 339, AP2022-179,  pp. 12-17,  Jan. 2023. [12] K.M. Keen,  “On the equivalent aperture formation of an endfire array,”  IEEE Trans Antennas Propag.,  pp 831-832,  Nov. 1974. [13] A.A. Oliner & R.G. Malech,  “Radiating elements and mutual coupling,”  in Microwave scanning antennas,  R.C. Hansen,  Ed.,  Academic Press Inc.,  vol. 2,  1966. [14] D.R. Hill,  “Commuted Doppler M.L.S. azimuth array feasibility demonstration model - first interim report,”  UK/MLS 2A/PIW/9,  The Plessey Company Ltd.,  20 May,  1974.    -180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180-20-15-10-5051015Angle (°)Directivity (dBi)φ=0° Eθφ=0° Eφφ=90° Eθφ=90° Eφ-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180-20-15-10-5051015Angle (°)Directivity (dBi)φ=0° Eθφ=0° Eφφ=90° Eθφ=90° Eφ- 21 -

Re-Examination of Watson’s Microwave Yagi Aerial

https://eprints.gla.ac.uk/323335/1/323335.pdf

Re-Examination of Watson’s Microwave Yagi Aerial

Abstract

Similar works

Full text

Available Versions

Enlighten