Introduction

As the title indicates, this page lists several different matching devices that can be used to match your antenna to your chosen feed line. Often the preferred feed line is unbalanced, low impedance coaxial cable (50/75 Ω), but some operators prefer using balanced feed line, like Ladder Line (75/300/450 Ω).

Some of the information on this page comes from a book written by William I. Orr, W6SAI called the Beam Antenna Handbook, 5th Edition. Its a fairly old book (1967) and I have taken some of the drawings from that book and regenerated/expanded/updated them. The original drawings only contained US/Imperial dimensions and equations plus it used some very outdated references, like MC (Mega Cycle) updated to MHz. I have also crossed the information with more current books, like the ARRL Antenna Handbook, 18th edition. Often the information was the same, but in some cases, it was slightly different. In many cases I also included a built in calculator that can be used to to generate information for your specific needs.

is specifically for creating a matching device that will allow you to use 50/75 Ω coax or 75/300/450 Ω Ladder Line with the 2 Element Yagi and 3 Element Yagi designs presented on this site, that have feed impedances between 18 and 22 Ω. The matching approaches can be used with any antenna. However, you need to be aware of the radiation resistance of your antenna. All matching techniques do not work, under all situations.

Delta Match (Balanced)

Delta Match Dimension Calculator
Input Data
Frequency: MHz
Output Data
Antenna Width (λ/2):
Feed Point Dimension:
Feed Point Width:
Delta Length:
A Delta Match is intended for matching a driven element to 300-600 Ω balanced feed line. A common dipole, driven from the center and 1/2 λ above ground, will exhibit approximately 72 Ω of impedance. While this will be balanced, it won't match the higher impedance balanced feedlines, which are in the range of 300-600 Ωs. However, if you move the feed points away from the center, the impedance will go up. However, there will be a point along the dipole where the impedance peaks.

While this matching device is included, it may not be a good choice.

The T-Match (Balanced)

T-Match Dimension Calculator
Input Data
Frequency: MHz
Diameter, D1:
Match Impedance:
Output Data
Dipole Length:
Diameter, D1:
Diameter, D2:
Spacing, S:
T-Rod Length:
Capacitance, C:
The diagram on the left is for a T-Match and it's pretty obvious why it is called the T-Match. The T-Match is and updated version of the Delta Match. However, the Delta Match was difficult to adjust and was made obsolete by matching devices that are easier to adjust. For that reason, the Delta Match will not be detailed on this web page. But if you are interested, you can probably find information on the Delta Match in some old antenna handbooks.

The T-Match incorporates resonating capacitors (variable) in each leg, to tune out the reactance of the T-Rods. The far ends of the T-Rods use adjustable metal straps to connect the T-Rods to the driven element. While the diagram shows that this is for matching high impedance, 300 Ω, balanced feed line, the matching network can also be used for matching low impedance, 75 Ω, balanced feed line. The length of the T-Rods, the spacing from the driven element, and the ratio of the diameter of the T-Rods to the driven element determine the impedance transformation.

The equations that are shown on the diagram generate US/Imperial dimensions. The calculator (above right) provides dimensions in both US/Imperial and Metric. In general, the T-Rods should be about 1/4 the diameter of the driven element (D2 = D1/4) and should be spaced away from the driven element by a distance equal to four times the diameter of the driven element (S = 4×D1). The length of the each T-Rod will be about 12% of the driven element, for a 300 Ω match and 9% for a 72 Ω match.

For example, the driven element for a 10 Meter 2-element yagi, designed for center frequency of 28.75 MHz, would be 16' 6-1/4" (4.974 m) in length (λ/2 (ft) = 471/FMHz) and would have diameter (D1) of 1-1/2" (38.1 mm). For a 300 Ω match, the T-Rods should be 0-3/8" (9.5 mm) in diameter (D2) and 1' 11-3/4" (604.3 mm) in length. The T-Rod spacing (S), from the center of the driven element to the center of the T-Rod, would be 6" (152.4 mm). The variable capacitors required for the match would be 210/F(MHz), or 7 pF.

For a 72 Ω match, assuming the same driven element, the T-Rods should be 0-3/8" (9.5 mm) in diameter (D2) and 1' 5-7/8" (453.2 mm) in length. The T-Rod spacing (S), from the center of the driven element to the center of the T-Rod, would be 6" (152.4 mm). The variable capacitors required for the match would be 210/F(MHz), or 7 pF

The T-Match (Un-Balanced)

λ/2 Balun Calculator
Input Data
Frequency: MHz
Coaxial Cable:
Output Data
Coaxial Cable:
Velocity Factor:
Impedance:
Balun Length:
The T-Match, from the previous section, can be combined with a λ/2 balun transformer, as shown in the diagram. Refer to the previous section for dimensions and a description of the T-Match.

The λ/2 balun transformer consists of a λ/2 loop of coaxial cable. The shields of the feed line and the loop are connected together and then bonded to the center of the driven element. The center conductor of the feed line is attached to the center conductor of one side of the λ/2 loop, and to one side of the balanced driven element. The center conductor on the other side of the λ/2 loop ties to the remaining side of the balanced driven element.

Note: The calculated Balun Length dimension is only for the shielded section of the coax loop. Make sure you add some extra length for connecting to the feed points.

The Gamma/Omega Match (Unbalanced)

Gamma-Match Dimension Calculator
Input Data
Frequency: MHz
Diameter, D1:
Match Impedance:
Output Data
Dipole Length:
Diameter, D1:
Diameter, D2:
Spacing, S:
T-Rod Length:
Capacitance, C:
I have clumped together the Gamma Match and the Omega Match in the same section because they are closely related. The Omega Match is a refined version of the Gamma Match.

The Gamma Match is effectively one half of a T-Match and is used to match your balanced antenna driven element, to unbalanced coaxial cable. It is probably the most comonly used matching device. It only uses a single Gamma Rod and a single series resonating capacitor, but the general characteristics of the T-Match apply to the Gamma Match.

Because the Gamma Match is unbalanced, the outer shield of the coaxial cable is connected (grounded) to the center of the driven element. Physically, using a solid driven element uncomplicates the possible mounting problems that split elements may provide.

The drawing on the left shows a version of the Gamma Match makes dual use of the Gamma Rod. Using hollow tubing for the Gamma Rod, a concentric capacitor can be made and used as the Gamma resonating capacitor. Polystyrene tubing is used as the dielectric for the coaxial rod-capacitor.

Using the dimension shown in the drawing, the capacitor has a capacitance of approxiately 15 pF per inch, engaged. The Gamma Rod setting is determined by the placement of the outer clamp. The Gamma resonating capacitor is then adjusted by loosening the inner clamp and moving the position of the outer aluminum tube. Two of these Coaxial Gamma Matches can be employed back-to-back to construct a Coaxial T-Match.

On the left is a drawing of the Omega Match, which is a expansion, or refinement, of the Gamma Match. In this version the Gamma Rod is made shorter than the normal Gamma Rod and impedance ratio adjustment is made by varying the capacity to ground, at the terminating end of the rod.

The Folded Dipole

The drawing on the left shows that, if you connect the ends of two half wave dipoles (one split at the center) together, it forms a Folded Dipole. If the two dipoles wires (tubes) are the same diameter, the radiation resistance will be about 280 Ω, at the split dipole point, and can be connected directly to a balanced transmission line.

The drawing on the right shows that, a similar multiplication of the feed point resistance can be had by connecting the ends of three half wave dipoles (one split at the center) together. In this case, the feed point resistance will be increased to about 630 Ω and can still be connected to a balanced transmission line. Again, this assumes that all of the wires (tubes) are the same diameter. This can be expanded to more λ/2 dipoles, with the feed point resistance being equal to 70 × N2, where N = Number of wires.

If you then assume that the radiation resistance of a simple dipole is 70 Ω, this shows that the Two-Wire dipole permits a 4:1 radiation resistance step-up ratio and the Three-Wire dipole permits a 9:1 radiation resistance step-up ratio. If the diameter of the wires (tubes) are different diameters, the step-up ratio can be varies over a wide range. The equations on the left show the relationship of the dimensions for a Two-Wire dipole.