This four-element cubical quad uses a multiturn driven element to obtain circular polarization. Essentially the design is a square Quadix. The elements are made of #12 copper wire and the boom length is 70″.
I optimized the design with the AO 8.50 Antenna Optimizer. This image shows the antenna geometry. Blue dots mark analysis segments. The red dot is the 300Ω feedpoint. The driven element spiral sense yields right-circular polarization.
Because it intercepts orthogonal power otherwise lost, in a circular field the Squadix has up to 3 dB gain over a linearly polarized antenna of similar size. It also suppresses crosspolarized multipath reflections, something an ordinary antenna can't do. But unlike dipole elements, loops do not have a natural null at 90°. I found that minimizing backlobes in the 120°-240° region yielded a better overall pattern than attempting to minimize them over the entire rear half-plane.
Below are calculated performance figures for 17 analysis segments per halfwave. Mismatch loss is due to SWR. Wire loss is due to conductor resistance. Mismatched gain is forward gain, including wire and mismatch losses. The gain reference is a linearly polarized dipole. F/R 120°-240° is the ratio of forward power to that of the worst backlobe from 120° to 240° to the rear. Ellipticity is the ratio of minimum to maximum linearly polarized forward response expressed in dB. The SWR reference impedance is 300Ω.
88.000 MHz: Impedance 278 - j106 ohms
SWR 1.45
Mismatch Loss 0.15 dB
Wire Loss 0.05 dB
Mismatched Gain 8.58 dBd
F/R 120°-240° 18.46 dB
Ellipticity -8.56 dB
93.000 MHz: Impedance 361 - j5 ohms
SWR 1.21
Mismatch Loss 0.04 dB
Wire Loss 0.03 dB
Mismatched Gain 8.79 dBd
F/R 120°-240° 23.51 dB
Ellipticity -2.49 dB
98.000 MHz: Impedance 370 - j4 ohms
SWR 1.23
Mismatch Loss 0.05 dB
Wire Loss 0.02 dB
Mismatched Gain 8.58 dBd
F/R 120°-240° 23.24 dB
Ellipticity -0.53 dB
103.000 MHz: Impedance 332 + j6 ohms
SWR 1.11
Mismatch Loss 0.01 dB
Wire Loss 0.03 dB
Mismatched Gain 8.75 dBd
F/R 120°-240° 20.93 dB
Ellipticity -3.06 dB
108.000 MHz: Impedance 210 - j25 ohms
SWR 1.45
Mismatch Loss 0.15 dB
Wire Loss 0.13 dB
Mismatched Gain 9.89 dBd
F/R 120°-240° 18.46 dB
Ellipticity -8.49 dB
Squadix Free Space 88 98 102 105 108 MHz 20 copper wires, inches re = 17.71295 de = 16.75463 d1 = 13.8253 d2 = 13.91915 pr = -23.06118 p1 = 22.59975 p2 = 46.37711 1 pr -re -re pr re -re #12 1 pr re -re pr re re #12 1 pr re re pr -re re #12 1 pr -re re pr -re -re #12 1 0.0 -de -de 0.5 de -de #12 1 0.5 de -de 1.0 de de #12 1 1.0 de de 1.5 -de de #12 1 1.5 -de de 2.0 -de -de #12 1 2.0 -de -de 2.5 de -de #12 1 2.5 de -de 3.0 de de #12 1 3.0 de de 3.5 -de de #12 1 3.5 -de de 4.0 -de -de #12 1 p1 -d1 -d1 p1 d1 -d1 #12 1 p1 d1 -d1 p1 d1 d1 #12 1 p1 d1 d1 p1 -d1 d1 #12 1 p1 -d1 d1 p1 -d1 -d1 #12 1 p2 -d2 -d2 p2 d2 -d2 #12 1 p2 d2 -d2 p2 d2 d2 #12 1 p2 d2 d2 p2 -d2 d2 #12 1 p2 -d2 d2 p2 -d2 -d2 #12 1 source Wire 5, end2 Trade-offs: Gain 67%, F/B 33% Worst/avg freq weighting: 80% 17 segments/halfwave F/B region: 120-240 deg Enable bent-wire correction
Symbols re, de, d1, and d2 are the element side lengths divided by two. Symbols pr, p1, and p2 are the reflector and director positions. The driven element position begins at 0 and advances 0.5″ per quarter turn. Use #12 bare copper wire, nonconductive element spreaders, and a nonconductive mast section near the antenna. Use a 75:300Ω current balun at the feedpoint. To further isolate the feedline, install a 75Ω current balun 30″ from the feedpoint.
88–108 MHz