Antenna Types
This lesson begins a series of 5 lessons related to antennas and feedline. It’s a good area to understand to maximize performance. The right antenna and feedline set-up can have a large impact on your ham radio enjoyment. Maybe even more than your choice of a transceiver. We’ll start by looking at some options for transmitting antennas.
Every location you want to operate from will have its unique challenges. Luckily there are lots of different transmit antenna options to choose from.
A long wire antenna is exactly what it sounds like. It’s generally a single, end fed wire. It’s very popular and useful for HF operations. It’s one of the simplest antennas to construct and erect. You put some wire between a tree and your house and you have an antenna.
There are two types to consider here. An End Fed Half Wavelength antenna usually has a balun so it is matched to your radio for transmitting. But, if you just want something for reception, any wire is better than no wire.
The length of the wire affects the radiation pattern. Here’s what happens when the wire length of an unterminated long wire antenna is increased. Additional lobes form with major lobes increasingly aligned with the axis of the antenna.
Illustration of a long wire antenna
A long wire makes a great receiving antenna. Especially on low bands like 160 and 80 meters. Gain is not a major factor with your long wire receiving antenna on those bands. This is because atmospheric noise is so high that directivity is much more important than losses.
Have you seen a rhombic antenna? It’s made up of 4 wires suspended in the shape of a 4 sided diamond. In geometry that’s called a rhombus. These are typically very large HF antennas but the design is used on UHF as well. Here’s a tip for modifying your long wire or rhombic antenna for different directional coverage. You can change the pattern of a rhombic antenna with a terminating resistor. The resistor changes the radiation pattern from bidirectional to unidirectional.
Rhombic antenna
Much time has been spent in courses covering the center fed, half-wavelength dipole. There are plenty of variants, and we’re going to cover a few. First, the folded dipole, which uses 2 half-wavelength wires in a U-shaped design.
Folded 1/2 wave dipole
A folded dipole antenna is a half-wave dipole with an additional parallel wire connecting its two ends. This additional wire changes the feed point impedance. At the center of a two-wire folded dipole antenna impedance is 300 ohms. For the most efficiency, feed this antenna with twin-lead cable. There’s more about twin-lead in an upcoming lesson.
The typical dipole has that feed point right in the center. Since that’s not always convenient there is the Off Center Fed Dipole or OFCD. Use a balun to feed an OCFD between the center and one end instead of at the midpoint. That allows you to create a similar feed point impedance on multiple bands.
If you prefer to have the feed point at the end of the antenna, consider a Zepp antenna. That’s more commonly known as an end-fed half-wavelength dipole. Portable HF ops like these for go kits. They are quick to deploy because only one end needs to be elevated.
An Extended Double Zepp antenna is a center-fed 1.25-wavelength dipole antenna.
One note on matching the OCF and End Fed antennas. A center fed dipole will have a 50 ohms match. But the match is different as you move away from the center. As you move to unmatched size elements, your balun needs to do more work. An OCF may use a 4:1 balun, while an end fed could use a 49:1 matching balun.
Typical Impedance Matching Baluns for Dipoles
| Center Fed | 1:1 balun |
| Off-Center Fed | 4:1 balun (depends on placement) |
| End-Fed | 49:1 balun |
There’s one HF antenna very popular for its size, price and effectiveness. We’re talking about the multiband G5RV antenna. A G5RV antenna is a wire antenna center-fed through a specific length of open-wire line connected to a balun and coaxial feed line.
The G5RV antenna is named with the call sign of the British ham who popularized it. Its special design has a vertical radiator at the middle of the antenna. This allows the G5RV to be compact because it’s shorter across the top than similar dipole antennas.
Phased Arrays
If one antenna is good, more could be better, right? A phased array uses multiple antennas to combine signals. Phased array antennas were originally conceived for use in military systems. A popular use today is for your 5G mobile service. Amateur radio gets in on the act as well. A phased array is often fed with signals from a computer controlled system.
We’re up to another one of those questions students find most difficult on practice tests. So, we’ll go into some extra detail. There are three important contributors to the radiation pattern of a phased array antenna system. They are:
- The length of the antennas,
- The distance between the antennas, and
- The phasing of the signal feed.
Let’s look at three antenna scenarios:
| Antenna Type | Antenna Spacing | Phase of Feed | Radiation Pattern |
| 2 ¼-wavelength vertical | ½-wavelength apart | In phase | Figure-eight broadside to the array. |
| 2 ¼-wavelength vertical | ½-wavelength apart | 180-degrees out of phase | Figure-eight oriented along the axis of the array. |
| 2 ¼-wavelength vertical | ¼-wavelength apart | 90-degrees out of phase | Cardioid. |
In all three cases we have an array of two ¼-wavelength vertical antennas. When fed in phase, the radiation pattern is a figure-eight broadside to the axis of the array. When fed 90 degrees out of phase, with tighter spacing, the radiation pattern is a cardioid. That is a heart shaped radiation pattern.
Now for the tricky one:
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase? In this case, it may be easiest to throw out the answers we have used. So we’ll toss out cardioid and broadside as an option. We know it’s not omni-directional because it’s not an isotropic radiator, so that goes too.
Here’s the correct answer. When fed 180 degrees out of phase the radiation pattern is a figure-eight oriented along the axis of the array.
Yagi Antennas
We can thank Dr. Hidetsugu Yagi and Dr. Shintaro Uda for the design of the Yagi-Uda Antenna, usually called a Yagi. They are directional antennas made of several short rods in parallel.
Let’s quickly review the parts of a Yagi antenna. In this image we have a 5 element Yagi.
It’s the driven element where the feedline is attached. That driven element is ½ wavelength long. That’s based on the intended frequency of the antenna. This is the active element in the antenna.
Remember from the General course the other elements are called the reflector and directors. The reflector and directors on a Yagi are termed “parasitic elements.” This is because they passively do their work to focus the signal. Yagi’s parasitic elements are either longer or shorter than the resonant driven element. That helps with control of phase shift.
A two element Yagi typically only has a driven element and a reflector. That allows for higher gain than using a director and driven element. As long as you are using normal spacing.
You can also create an array of Yagi antennas. A ham can pair up 2 meter and 70 centimeter yagi antennas to work cross-band satellites. How do you produce circular polarization with two linearly polarized Yagi antennas? Arrange two Yagis on the same axis and perpendicular to each other with the driven elements at the same point on the boom and fed 90 degrees out of phase.
Illustration of perpendicular yagi
The key word here is perpendicular. This is the only answer that has the two Yagi antennas arranged perpendicular to each other.
Specialized Receiving Antennas
Earlier, we mentioned the long wire as a good receiving antenna. More specialized receiving antennas are called beverage, loops and pendants.
One good example of a receiving antenna is the Beverage antenna. It’s composed of two horizontal elements. Picture two wires connected between two trees. One element is the radiator and the other acts as a counterpoise or artificial ground. The two elements are connected via feed-line and a separate resistor link.
An example of a Beverage antenna
Want good beverage antenna performance at your desired frequency? Consider two key design factors. First, your elements should be at least one wavelength long. Second, pay attention to the terminating resistor. Its function allows it to absorb signals from the reverse direction. Most important is selecting the correct resistance value. That will provide minimum variation in SWR over the desired frequency range.
If you don’t have room for a Beverage antenna, you can compromise. A smaller alternative is called a Pennant antenna. A Pennant antenna is a small, vertical, triangular shaped terminated loop. This design creates a cardioid radiation pattern, which is heart shaped.
Or how about an old school option? In the early days of radio, many receivers were equipped with a multi-turn receiving loop antenna.
This diamond-shaped is great for receiving in the AM Broadcast and 160 meter band. The output voltage of a multiple-turn receiving loop antenna can be increased. Do that by increasing the number of turns and/or the area enclosed by the loop. These are a bit similar in function to the low-power mag-loop antennas some hams use today.
