If you’re looking for a high-performing omnidirectional antenna, consider this design. It boasts 5 collinear radiant elements that are connected by phasing coils. The feed point is conveniently located at the base of the antenna on a J dipole. By adjusting the position of the feed point along the J, you can minimize the SWR. At the top end of the antenna, you’ll find a small loop that serves as a tie point, measuring just 1/2″ in diameter. The total length of the antenna is 295″. Each coil features 32 turns and has a diameter of 5/8″.

To accurately model this design, we should use simulation software that is capable of modeling curved wire segments and small, closely-spaced wires. With AN-SOF, you can use the “Helix” object to perfectly model each coil. By using only one segment per turn, this model demonstrates the efficiency of AN-SOF in simulating complex designs.

Download >

Simulation of a multiband dipole for 3.7, 7.05, 14.2, 18.1, 21.2, and 28.5 MHz.

There are 6 dipoles of almost half a wavelength each. They are all connected to the same feed point.

This is an example where we need simulation software capable of modeling very close wires.

Download >

The so-called “Loop on Ground (LoG)” is a small loop antenna with a cardioid-shaped radiation pattern in the horizontal plane, used for reception.
The loop has a 110 Ohm resistor connected to its top, while the antenna terminals are located at the bottom. One of the terminals is connected to ground by a vertical wire, forming a monopole. This is the secret to getting this antenna, despite being small, to be directional.
The image below shows the radiation patterns obtained with and without grounding.

Frequency: 4.5 MHz
Loop diameter: 1 m
Height above ground: 2 m (average real ground)

The segmentation used in the Conformal Method of Moments is observed over the antenna. Very few segments are needed because it is a small antenna in terms of the wavelength.

Download >

At Golden Engineering we are passionate about antenna simulation. On this last day of the year we want to give you our Log-Periodic Christmas Tree made with AN-SOF:

Download >

We thank all our clients, users and people who collaborate so that the AN-SOF Antenna Simulator project continues to grow day by day.

Happy New Year!

This small transmitting loop antenna is 1 meter high above average ground, so the radiation pattern is not donut-shaped as expected for a small loop in free space. The value of the tuning capacitor is indicated for each resonance frequency.

Large loop: 70 cm in diameter, RG-8 cable.

Small loop: 15 cm in diameter, RG-6 cable. Inductive coupling between the feedline and the large loop, spacing of 2 cm.

The color scale on the loops indicates the current flowing for a reference voltage of 1 V.

Download the project files from this link >.

Go to AN-SOF main menu > Run > Run Bulk Simulation and select the five “.nec” files to run the calculations automatically. You can do it with the trial version of AN-SOF.

This Quadrifilar Helix (QFH) antenna, also known as QHA, can be used for signal reception from NOAA satellites. These are omnidirectional antennas made up of 4 wires with a helical shape. This design is about 0.14λ in diameter and the length of each helix is 0.4λ. It resonates at 137.5 MHz and has a bandwidth of 6% (SWR < 2). The purpose of the helices is to block surrounding interference.

In free space, the radiation pattern actually points downward when the coaxial cable (the source in the simulation) is connected to the top of the antenna. However, when a real ground plane is added and the antenna is placed 5 meters high, multiple lobes and a more omnidirectional pattern are obtained, as expected.

Download >

This Moxon antenna variant resonates at 145 MHz.

Input Impedance: 47 Ohm
Bandwidth: 7% (VSWR < 2)
Gain: 6.3 dBi
F/B: 19 dB
Beamwidth: 130°H / 80°V

Download >

This 4-element biquad array resonates at 434 MHz. The wires that connect the driven element to the reflector work as a two-wire transmission line that allows us to obtain an input impedance of 50 + j0 Ohm.

It may be noticed that the polar plots are on a log scale. ARRL-style log scaling is coming in the December release of AN-SOF!

More info >

This is a 4 element broadband directional antenna. More than 50 MHz of bandwidth (SWR < 1.5) around 285 MHz. Gain 7 to 8 dBi. Length 0.52 m and maximum width 0.6 m.

The driven element is shaped like a double arrow and has a folded parasitic element right in front of it.

Download >

From this link > you can download 5 examples of antenna models that have less than 50 segments, so the calculations can be run with the trial version of AN-SOF:

• 2 Element Quad
• 2 Element Delta Loop
• HF Skeleton Slot
• Inverted V
• 5 Element Yagi-Uda

It is an array of two tightly coupled loops with a bi-directional pattern. Both loops are linked to share a single feed point. This antenna can operate in the 14 to 28 MHz bands with the appropriate impedance matching. It is self-resonant when the perimeter of each loop is around one wavelength. In this example, each loop is 3 x 4.5 m and the resonant frequency is 19.8 MHz.

Download >

This design is for 5 bands on a single pole. Each “J” corresponds to a band and therefore the feed point changes depending on the frequency. The resonance frequency is indicated in each case, which can be changed by moving the feed point. The height is about 5 m.

Download >

Here is a relatively compact array of 5 square loops for 145 MHz. It does not need a matching network since the input impedance is practically 50 Ohm. Gain 12 dBi. Beamwidth 50 deg. F/B 20 dB.

Download >

These are compact, lightweight antennas that can be used for DX applications. This 2-element array is the simplest we can build to get a directional antenna using delta loops. It is practically resonant with 50 Ohm of input impedance near the band center. This is an example where we need to enable the Exact Kernel option in AN-SOF since we have sharp angles between wires.

Download >

This model is self-resonant (50 Ohm) in the analyzed frequency range, so it does not need a matching network. Adjust the indicated gaps to minimize the VSWR.

Download VHF >

Download UHF >

2-element quad antennas are very popular due to their compact size and gain similar to a more element Yagi. In addition, they can be designed to obtain an input impedance of 50 Ohm.

This design can operate at 27.5 MHz. We have added a script that allows us to plot the gain and front-to-back ratio as a function of element spacing. See this video >.

We can see that both cannot be maximized at the same time, but it is preferable to choose the maximum F/B since the gain changes relatively little.

To create the Scilab script, we started from a basic design in AN-SOF and then exported it as a *.sce file.

Download Model >

Download Script >

A half-wave dipole would have a length of 40 meters in this band (3.75 MHz), difficult to install at home due to lack of space. Not to mention the complaints from our neighbors.

A spiral loop is attractive for its small size and relative ease of tuning because it is basically an inductor to which a variable capacitor is connected at the feed point to achieve resonance. However, the radiation resistance is extremely small, on the order of milliohms and therefore the efficiency is very low.

Unfortunately any small loss severely affects the antenna efficiency, such as losses in the capacitor, wires, interconnections, solder joints, surrounding objects, ground plane, to name just a few. In fact, this antenna can be tuned and get a wide bandwidth thanks to all the losses. The maximum radiation occurs upwards when the antenna is installed vertical to the ground plane, so some have suggested installing it horizontally. We should emphasize, however, that it is a popular design due to its ease of installation and small size, but we must be careful because high voltages can be expected, especially in the tuning capacitor.

This AN-SOF model consists of a frame of 50 cm on each side (0.00625 of the wavelength) with 7 turns of wire. This is another example where we need to simulate with very short wire segments, very close to each other and bent at right angles.

In these results we can see the effect on the input resistance of adding losses in the ground plane and surrounding objects, such as a wall,

Perfect ground: 4 milliohm
“Cities industrial poor” ground: 1.3 Ohm
“Cities industrial poor” ground + wall: 49 Ohm

This design can be easily transformed into a multi-band antenna by shorting turns of wire, much like a variable inductor, to make it operate on the 40, 30 and 20 meter bands.

Download >

Small helical antennas for the 433 MHz ISM band are a good example where we need advanced software that has the ability to model: 

• curved wires with exact description of the helix contour

• very close wires, spaced a fraction of the wire radius

• horizontal wires almost touching the ground plane

• bent wires at right angles or less

• short segments, below 0.001 wavelength

• thick wires by means of Exact Kernel instead of thin-wire approximation

AN-SOF includes all these features.

In this example, a perfect ground plane is used to get the input impedance: 48 Ohm, very close to the 50 Ohm of the antenna datasheet. We must subtract 3 dBi from the gain to obtain the gain in free space. It is a simple model, but it coincides very well with reality.

Download >

Nathan Cohen in the US fractalized the quad loop based on the Minkowski square and invented an array of two elements. The biggest advantage of fractal antennas is that we get a wide bandwidth with a small size.

This simulation shows that we can almost double the bandwidth with a 3-element array. It has a reflector, a driven element, and a director. These are the results for the 20 m band (~ 14 MHz),

Quad size ~ 290 x 290 cm (0.14 x 0.14 of a wavelength)

Element spacing ~ 280 cm

450 KHz bandwidth (VSWR < 2) around 14.5 MHz

6 dBi gain

10 dB F/B

80° beamwidth

Vertical polarization

It has less gain than could be achieved with a 3-element Yagi, but it has a relatively large bandwidth and is a very compact antenna. It does not need a matching circuit and its impedance is 50 Ohm at resonance, so it could be fed directly through a 50 Ohm coax.

Download >