T-antenna

T-antenna is a very simple antenna having the form of the letter T. As shown in the picture below, the antenna seems to be most useful when used with receivers having one single antenna connector (e.g. banana socket).

The antenna is very simple and is completely not resonant. You can easily tune its active resistance (Rx) by changing the length of wires. Unfortunately, the non-resonant nature of the antenna won't allow you to move the Jx (reactance) of the antenna close to zero. The figure above shows the good pattern but the awful resistance of antenna Zx = 53 + 25657j. The SWR is awful too: 245380 on 50 Ohms. The given results were obtained for the antenna about 13 meters tall having 15 meters long top piece. Please note, that the active resistance depends on a very small change of the wires, whereas reactance remains almost intact regardless of the changes you can make against wires.

But there is always the way to improve. In order to manage the reactance, you have to add just a small counterpoise. This changes the Zx of the antenna as well as its SWR and emission pattern. But, at least, it becomes resonant. And it is quite wideband, the SWR by 2:1 is about 350 kHz.

By the way, after adding counterpoise the antenna becomes a GP with a capacitive load on the top.

Below is the model of the T-antenna with counterpoise.


*
14.15
***Wires***
4
0.0, 0.0, 12.5, 0.0, 0.0, 0.8, 8.000e-04, -1
0.0, 0.0, 12.5, -5.6, 0.0, 12.4, 8.000e-04, -1
0.0, 0.0, 12.5, 5.0, 0.0, 12.4, 8.000e-04, -1
0.0, 0.0, 0.8, -4.5, 0.0, 0.3, 8.000e-04, -1
***Source***
1, 0
w1e, 0.0, 1.0
***Load***
0, 0
***Segmentation***
800, 80, 2.0, 2
***G/H/M/R/AzEl/X***
0, 20.0, 0, 50.0, 120, 60, 0.0