UHF+Hi-VHF Vertically Stacked mclapp M4 (9.5x9-in) 4-Bay Bowties with Double Angled Reflectors (40" H x 36" W using 1x2-in Grid) were analyzed using 4nec2, where Zmm = Metal-to-Metal Separation between Reflectors.
A set of Parametric Sweeps for Zmm were conducted at 470, 584 and 698 MHz, which found that there was only about +/- 0.2 dB Raw Gain difference as Zmm was varied. SWR (300-ohms) was also Excellent, although rising slightly above 2.7 on 470 MHz at Zmm=6.25 to 8.25-in, with only minor F/B & F/R Ratio differences.
Many times Multipath will result in signal strength varying with height in alternating Peaks and Nulls. Zmm was chosen so that when Nulls form across the Bowties on one Antenna, hopefully Peaks will form across the Bowties on the other. Hence they are NOT at equal spacing across the entire Stack, as is found in many Narrow Band Antenna Arrays. In fact, per the Charts, with equal Bowtie spacing (Zmm=7.25-in) Raw Gain, F/B & F/R Ratio would all be lower.
Three Versions with only slightly different performance are presented here. The first two place equal strength SOURCEs at the Feedpoint of each 4-Bay to assess what is achievable if fed from a "Perfect" RF Combiner. The third uses an Optimized Vertical Harness to interconnect the 4-Bays, which can be expected to provide better performance in the "Real World":
a) RF Combiner Mod (with 0.5 to 1.5+ dB Combiner Loss NOT included): "Best" Gain is a compromise, between Zmm= 2.25 to 4.25-in. Results are presented for Zmm=2.75-in, for "Best" Anti-Multipath performance. Beamwidth narrows from 40 to 30-degrees.
UHF Raw Gain = 16.9 to 18.6 to 18.5 dBi, F/B & F/R Ratio = 19.4 to 16.1 dB and SWR (300-ohms) under 2.6. Hi-VHF Raw Gain = 11.2 to 11.9 dBi, F/B & F/R Ratio = 13.6 to 18.8 dB and SWR (300-ohms) = 3.0 to 12.2.
############################################################ b) RF Combiner Mod (with 0.5 to 1.5+ dB Combiner Loss NOT included): "Best" F/B & F/R Ratios (at the expense of small Gain reduction) is at Zmm=10.25 to 11.25-in. Results are presented for Zmm=11.75-in, for "Best" Anti-Multipath performance.
UHF Raw Gain = 16.7 to 18.5 dBi, F/B & F/R Ratio = 20.7 to 16.3 dB and SWR (300-ohms) under 2.5. Hi-VHF Raw Gain = 11.9 to 12.1 dBi, F/B & F/R Ratio = 14.8 to 20.3 dB and SWR (300-ohms) = 3.5 to 13.2.
Azimuthal Pattern Charts are nearly identical to those for Zmm = 2.75-in.
############################################################ c) Vertical Harness Interconnecting the Two 4-Bays. Results are presented for Zmm=2.75-in, for "Best" Anti-Multipath performance. Beamwidth narrows from 40 to 30-degrees.
UHF Raw Gain = 16.8 to 18.2 dBi, F/B & F/R Ratio Min = 15.4 dB and SWR (300-ohms) under 2.4. Hi-VHF Raw Gain = 11.0 to 11.7 dBi, F/B & F/R Ratio Min = 14.2 dB and SWR (300-ohms) = 1.6 to 36 is Excessive, except lowest channels.
Since lossy RF Combiner is not required, Vertical Harness version is preferred for UHF Band.
===================================== UPDATE (9Feb2017): Conducted a "What-If" Investigation on third Alternative (c, with HVH) to ascertain effect of extending BowLength for operation in New, New UHF Band [Ch14-36].
If SWR is kept no higher than 2.7 [Mis-Match = 1 dB], only a couple TENTHS of a dB Gain increase are possible at BowLength = 10.5-in.
If SWR is allowed to be as high as 3.2 (Mis-Match = 1.4 dB), Gain Increase of 0.3 to 0.5 dB is possible at BowLength = 11.25-db....hardly worth the effort....
Date(s): 9 Dec2013. Album by holl_ands. 1 - 72 of 72 Total. 3257 Visits.
enlarge 188KB, 1152x689 1 Vert-Stack M4 - Vary Zmm at 470 MHz Raw Gain Max at Zmm = 4.25 to 6.25-in F/B & F/R Ratio Max at Zmm = 10.25 to 12.25-in
enlarge 181KB, 1152x689 2 Vert-Stack M4 - Vary Zmm at 584 MHz Raw Gain Max at Zmm = 0.25 to 2.25-in F/B & F/R Ratio Max at Zmm = 8.25 to 14.25-in
enlarge 184KB, 1152x711 3 Vert-Stack M4 - Vary Zmm at 698 MHz Raw Gain Max at Zmm = 0.25 to 2.25-in and Zmm = 12.25 to 16.25-in. F/B & F/R Ratio Max at Zmm = 6.25 to 10.25-in
enlarge 237KB, 1024x662 4 Vert-Stack M4 - Vary Zmm at 470 MHz SWR (300-ohms) Just Over 2.7 at 470 MHz for Zmm = 6.25 to 8.25-in, otherwise Excellent.
enlarge 234KB, 1024x663 5 Vert-Stack M4 - Vary Zmm at 584 MHz SWR (300-ohms) is Excellent for all Zmm.
enlarge 239KB, 1024x666 6 Vert-Stack M4 - Vary Zmm at 698 MHz SWR (300-ohms) is Excellent for all Zmm.
enlarge 295KB, 609x1024 7 Vert-Stack M4 - AntiMP at Zmm = 2.75-in "BEST" UHF RAW GAIN 3D View
enlarge 232KB, 639x1024 8 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Front View [1 large square = 12.5 inches]
enlarge 120KB, 361x1024 9 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Top View [1 large square = 2.5 inches]
enlarge 170KB, 1152x711 10 Vert-Stack M4 - AntiMP at Zmm = 11.75-in UHF Raw Gain = 16.9 to 18.6 to 18.5 dBi UHF F/B & F/R Ratio = 19.4 to 16.1 dB
enlarge 213KB, 1152x711 11 Vert-Stack M4 - AntiMP at Zmm = 2.75-in UHF SWR (300-ohms) Under 2.6
enlarge 210KB, 619x1024 34 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT 3D View
enlarge 229KB, 639x1024 35 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Front View [1 large square = 12.5 inches]
enlarge 202KB, 636x1024 36 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Top View [1 large square = 2.5 inches]
enlarge 170KB, 1152x714 37 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT UHF Raw Gain = 16.8 to 18.2 dBi UHF F/B 7 F/R Ratio Min = 15.4 dB
enlarge 216KB, 1152x714 38 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT UHF SWR (300-ohms) Under 2.0
enlarge 22KB, 791x1024 48 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Contents of Python Control Script *.bat File
enlarge 188KB, 1152x714 49 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Hi-VHF Raw Gain = 11.0 to 11.7 dBi Hi-VHF F/B & F/R Ratio Min = 14.2 dB
enlarge 214KB, 1152x714 50 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Hi-VHF SWR (300-ohms) = 1.6 to 36 is EXCESSIVE, except lowest channels
enlarge 303KB, 1024x1024 52 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Azimuthal Pattern at 174 MHz
enlarge 303KB, 1024x1024 53 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Azimuthal Pattern at 198 MHz
enlarge 306KB, 1024x1024 54 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Azimuthal Pattern at 216 MHz
enlarge 86KB, 539x1024 55 Vert-Stack M4 - AntiMP at Zmm = 2.75-in ONLY VERTICAL HARNESS & BOWTIES 3D View
enlarge 178KB, 481x1024 56 Vert-Stack M4 - AntiMP at Zmm = 2.75-in ONLY VERTICAL HARNESS & BOWTIES Front View [1 large square = 12.5 inches]
enlarge 171KB, 719x1024 57 Vert-Stack M4 - AntiMP at Zmm = 2.75-in ONLY VERTICAL HARNESS & BOWTIES Top View [1 large square = 2.5 inches]
enlarge 85KB, 694x1024 58 Vert-Stack M4 - AntiMP at Zmm = 2.75-in ONLY VERTICAL HARNESS & BOWTIES 3D View - DETAIL
enlarge 117KB, 360x1024 59 Vert-Stack M4 - AntiMP at Zmm = 2.75-in ONLY VERTICAL HARNESS & BOWTIES Side View [1 large square = 5 inches]
enlarge 102KB, 398x1024 60 Vert-Stack M4 - AntiMP at Zmm = 2.75-in VERTICAL HARNESS INTERCONNECT Side View [1 large square = 12.5 inches]
enlarge 218KB, 1152x701 61 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength Raw Gain at 470 MHz Increases with Length
enlarge 244KB, 1152x701 62 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength SWR (300-ohms) at 470 MHz Excessive if BowLength 14-in or more
enlarge 268KB, 1152x701 63 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength Impedance at 470 MHz
enlarge 231KB, 1152x701 64 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength Raw Gain at 578 MHz Broadband Maximum at 11.5-in +/- 1-in
enlarge 233KB, 1152x701 65 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength SWR (300-ohms) at 578 MHz NOT Acceptable for Bowlength 10.75 and above
enlarge 268KB, 1152x701 66 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength Impedance at 578 MHz
enlarge 218KB, 1152x701 67 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength Raw Gain at 614 MHz Broadband Maximum at 11.25-in +/- 1-in
enlarge 233KB, 1152x701 68 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength SWR (300-ohms) at 614 MHz Acceptable at any BowLength up to 14.5-in
enlarge 276KB, 1152x701 69 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength Impedance at 614 MHz
enlarge 225KB, 1152x701 70 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength Raw Gain at 698 MHz Decreases for higher BowLengths
enlarge 237KB, 1152x701 71 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength SWR (300-ohms) at 698 MHz Acceptable at any BowLength up to 14.5-in
enlarge 266KB, 1152x701 72 Vert-Stack M4 - AntiMP at Zmm = 2.75-in Effect of Extending BowLength Impedance at 698 MHz
I just found your guest book access at the bottom of the page. I want to thank you for your research and work. The latest version antenna i've made is having exellent results. After experimenting with the various combining alternatives I wound up locating some belden shielded twinlead which made for a much more convenient routing solution without interference from the metals in close proximity to it or adding wind load strain. Someone in the past around here sold cm-4221's as there are an abundunce of old ones still around making for easy access to parts. Thanks again, Evan Green - Evan Green, Mon, 22 Dec 2014 11:31AM
