Hi-VHF Circular Loop with either Loop or Screen Reflector analyzed using 4nec2. With Loop Reflector, Net Gain was 8 dBi on Ch7, dropping to 6 dBi on Ch13 with excellent SWR, except for small increase on Ch7.
Adding Loop Reflector increased Net Gain by 2-4 dB (less at high freqs) with more than 8.7 dB F/B (and F/R) using
Optimum Diameter=24-in for Half-Inch Copper Tubing. Best F/B (and F/R) is on Ch8-10.
Optimum Diameter=23-in for Quarter Inch Copper Tubing (QICT) was nearly as good, with more than 7.3 dB F/B (and F/R). Smaller Circular Loop Element sizes not analyzed since a Square Loop (Quagi) would be easier to construct.
Loop Reflector dimensions are optimized for full Hi-VHF Band coverage. Rescaling to optimize Ch7 will have only minor-moderate impact to Ch13 F/B, F/R and SWR. However, rescaling to optimize Ch11-13 will degrade F/B, F/R and especially SWR on CH7-10.
EDIT (16 Sep 2009): Added analysis of alternative Hi-VHF Loop with Screen Reflector.
Date(s): 15 July 2009. Album by holl_ands. 1 - 20 of 29 Total. 729 Visits.
enlarge 0KB, 1024x840 1 Hi-VHF Circular Loop w. Loop Reflector - 3D View
enlarge 0KB, 1024x696 2 Hi-VHF Circular Loop w. Loop Reflector Raw vs Net Gain vs SWR (300-ohm) for Half-Inch and QuarterInchCopperTubing (QICT).
enlarge 0KB, 1024x696 3 Hi-VHF Circular Loop w. Loop Reflector Dimensions are for a "balanced" design with EQUAL F/B and F/R at highest and lowest freqs.
enlarge 0KB, 1024x819 4 Hi-VHF Circular Loop w. Loop Reflector Raw Gain, F/B and F/R Ratios
Optimum Diameter=23-in for Half Inch Copper Tubing (OD=0.514)