They are simple antennas that have omnidirectional radiation or reception, in the horizontal plane if they are vertical. They don't radiate along the antenna axis. This is very convenient for broadcast which by definition of broadcast wants to go in every direction, but on earth usually means towards the horizon all round.

They are good for applications where you don't know where the signal is coming from or going to. More complicated antennas have better reception or more power on target, but only if they are pointing in the right direction.

Design Of Monopole Antenna And Half-Wave Dipole Antenna For Wi-Fi Applications By Enhancing Gain

https://ieeexplore.ieee.org/abstract/document/9426126

You can't enhance the gain of a quarter-wave monopole or half-wave dipole much, except by not making them badly.

In the AM broadcast band, monopoles are used (not dipoles) because of the large sizes (heights) required. In this case, the other half of the antenna is what is the counterpoise (an old term) which is the ground itself ... whose conductivity is sometimes augmented by burying additional wires in the ground.

They are useful because of the physics of the problem. For example, a quarter wavelength monopole at 1000 kHz is about 75 meters.

Dipoles are used in FM broadcasting where the smaller size allows other options.

Dear Obert Mutava ,

I would second my respected colleagues above and add in order to cover the largest volume from space around them the antennas is best be in shape of a dipole. In case of long antennas, one would use only a monopole. to save half of the length of the antenna. In addition to their simplest construction.

If it is required to direct and collect the electromagnetic waves in certain direction then one has to use antenna arrays of surface antennas.

Best wishes

The Chu-Harrington limits give us a limiting relationship between bandwidth and efficiency for small antennas as a function of the subtended volume (a sphere) of the antenna in wavelengths^3. It is a compelling study and explains that the efficiency of any antenna drops very rapidly as the diameter of the subtended sphere goes below a half-wavelength.

The bottom line is that an effective small antenna is primarily a matter of aperture: that is, how much space it requires. A dipole is a favorable candidate here as it acts as an efficicnt transducer to connect a transmission line to a free space electromagnetic wave. You can make it smaller than a dipole but, in priciple, you cannot overcome the Chu Harrington limits.

Keep in mind that the Chu-Harrington limits were derived for a two-pole radiator. You may derive some bandwidth improvement (see Bode-Fano limit) where Chebyshev matching sweeps up more available bandwidth ... but at a cost.

Dear Leslie Reading we can overcome the Chu Harrington limits if use few dipoles inside the radiation volume (a sphere). About such fact, you can read in this article (page 13):

Article 60 Years of Electrically Small Antennas Theory. Some Conclus...

A remarkable paper! Thank you. I will spend the next few days tracing through the thoughts contained here so that I can integrate them into practical antenna design.

As an long-term antenna designer, I am often confronted with customer constraints that violate physics. The Chu-Harringtom limits have been the heart of many of my explanations. It's been several years since I've been down this path but now I have the priviledge of refreshing my explanations.

With respect to the orignal post for this thread, I think this article is required reading for someone seeking insight into why we use monopoles and dipoles as it covers the fundamental limitations.

Thank you again for your excellent input.

Vadym Slyusar

You are right when you say not all scientists share Grimes' optimism. I am extremely sceptical. I have tried to understand papers by Grimes and Underwood but their assumptions and equations do snot seem to correspond to reality.

In case of long antennas, one would use only a monopole to save half of the length of the antenna where one wire is connected to the ground. To save the loss of energy during transmission. The antenna's reflecting surface allows waves reflected by it to maintain their phase connection, allowing the greatest gain to be achieved. By changing the length of this single wire, it will be able to resonate at a particular frequency.

Just remember about supergain antennae..they have a surprisingly good directivity even when the array is smaller than a wavelength..but at the expense of criticality

In nearly every case supergain antennas are very inefficient, so although the beam may be narrow (high directivity for the size of antenna) the gain is usually lower than normal for the size of antenna.

There is a common misunderstanding with the term "Gain of an Antenna". When the purpose is to cover as wider an area as possible, we actually need antenna with lower gains. That purpose is served by monopoles and dipoles as their radiation pattern is omnidirectional. It can direct the EM waves in the space surrounding them with almost no radiation in direct upward/downward directions.

If we need antennas that are directional, we shall need antenna with higher gains, for example if we want to do sectoring in a cell, we shall need more directive antennas. This can be achieved by creating arrays of antenna with various geometric configurations.

You will find relevant useful information in the following papers:

Article A Compact CSRR Enabled UWB MIMO Antenna

Article Eight-Element Compact UWB-MIMO/Diversity Antenna with WLAN B...