Generally folks who have done radio stuff for a while know you can take your basic dipole of two straight wires and bend those wires in various ways while still getting an OK antenna out of it.
This takes all sorts of forms. Inverted V. “Bent Dipole” where you just sort of droop the ends. all sorts of shapes have been given specific names. Yet this one was new to me. The Z shaped dipole.
The paper, linked below, most likely is very clearly saying in what direction to bend the arms to make the Z but they assume there is some standard axis for X Y and Z relative to ground. A standard, if I ever knew it 50 years ago when more serious about this stuff, I’ve long ago forgotten. For the basic antenna, the ‘feed’ is in the middle of the Z and the two wires are bent about the middle. My impression was that the Z is in the front to back plane, but others will need to sort that out. It might work just as well if the ends are in the up-down or right-left, though perhaps with some change of polarization. Here’s the link to the paper:
2.1 Antenna Structure
This antenna is made of a Z-shaped thin wire and is fed symmetrically as shown in Figure 1. The antenna is located in the
xz–plane. The fractal first, second and third iterations of Z-shaped dipole antenna are depicted in figures 2, 3 and 4. Each iteration is formed by replacing the half of the free arm of Z-shape by another Z-shape. All of these antennas have the same wire length (202 cm) and a radius of 0.1 cm. The MoM with one-volt delta gap source is applied to theses antennas. The previous antennas occupy different spaces as shown in the figures and table 1. The antenna performance properties are obtained using commercial software (NEC-WIN Pro V.1.6)
It would be nice if they had labeled their graphs. ( I remember my high school algebra teacher giving us great grief for any graph with unlabeled axis. )
The paper then goes on to look at fractal derivations. For those, some of the main central wire, and the end segment is itself bent into another Z for a first order fractal. Then again for a 2nd order and so on to 3rd order. This image is the first step:
Two things about this got my attention. First off, it is just a wire. Nothing really fancy going on here with cutting slots or making flag shaped pennants or needing to hold circular shapes.
Second, when I read the gain figures I was a bit surprised. I am used to the idea of a dipole being basically a ‘no gain’ vs a reference standard dipole, even if bent. Here’s the chart of gain (from Table 4, 7th page #145):
Antenna 400 MHz 900 MHz 1900 MHz Z Dipole 4.4 dB 4.1 dB 10 dB (Honest, I read it twice. 10) 1st Iter 3 dB 7.5 dB 2.0 dB 2nd Iter 5.1 dB 4.9 dB 5.5 dB 3rd Iter 4.8 dB 4.53 dB 3.9 dB
All I can figure is that the long wire is acting off the ends as a long wire multiple wavelength for that 1900 MHz one, or maybe their reference is not a ‘standard dipole’.
By the time you are at the 3rd Iteration, the antenna fits in a 40 cm by 51 cm box. Now the TV range I’m trying to pick up runs about that 400 to 900 range, so something in this size or double ought to work. Call it a meter by 80 cm. Given that the 2nd iteration is a bit more gain and still fits in a 45 x 50 cm box, it is likely the one I’d use.
For two bent wires and nothing else. Makes a fella go “Hmmmm….”
From the previous figures we notice that the fractal ZDA has superior performance over the linear dipole. The linear dipole is resonant antenna but fractal ZDAs show broad characteristics. The fractal ZDA has superior current distribution at the linear dipole. The main difference between these two antennas is the polarization where the linear dipole is linearly polarized antenna [1,2] but fractal Z-shaped dipole antenna is elliptically polarized antenna.
Remember that a circularly polarized antenna is an elliptically polarized one that is radially equal…
The two handednesses have opposite circular polarization, so a dipole of one each would pick up both circular polarizations along with horizontal and vertical linear polarizations. Equally out front and back.
Now that’s an interesting antenna… especially since shifts of polarization at UHF from reflections is one of the most annoying kinds of ‘fade’ and ‘flutter’ to deal with. Go ahead and shift, or rotate, or whatever, this antenna just won’t give a damn…
FWIW, if I’m reading the graphs correctly, down in the 400 MHz range the standing wave ratios et. al. are a bit more peaky, then smooth out at the higher frequencies. This implies a (still small…) double size one would be even better at multiband. This one looks to have been designed for the peak at lower frequencies to be usable at that frequency, then pick up the upper bands as near harmonic and broader band segments. As I’m not interested in 1900 MHz, I’d look to make the thing larger to put the base at about 200 MHz and then 400 to 800 in that nice upper range.
The other interesting potential this raises is testing some “Z Dipole” log periodic layouts… but that would take math involving logs and this is a weekend ;-)