An optimum antenna is crucial for every radio system!

Die Antennen wurden bei den Handys immer kleiner. Bei den heutigen Smartphones sind sie gar nicht mehr sichtbar.

First of all, the most important thing to remember is that every radio link always requires an antenna at the transmitter and at the receiver, without exception. Just like in the past, a good antenna still requires a great deal of attention today. This is because a poorly matched antenna can easily give away 50% or more of the radio range. Even modern smartphones still have various antennas, but these are usually integrated in a miniaturized way and invisible to the user directly in the housing, with the disadvantage that the antenna efficiency and thus the radio range is somewhat worse than before. However, this disadvantage is compensated for by an increasingly dense mobile network. On the other hand, the design of the smartphone has been modernized, which is a decisive factor for sales in particular.

This example clearly illustrates that when developing a wireless system, a compromise often has to be found between the optimum efficiency of the antenna and the optimum design of the housing.

What should a good antenna look like?

Antennas come in many different sizes and shapes. An appropriate antenna can be developed for a product based on the radio frequency, the requirements of the application and the space available. Basically, the higher the radio frequency, the smaller the antenna. A radio, for example, requires a much longer antenna than a WLAN device, as the radio frequency of the radio is much lower than that of the WLAN. The optimum length of a simple rod antenna can be calculated based on the radio frequency used.

Length of the rod antenna = speed of light / (radio frequency*4)

This results in an optimum antenna length of 17.3 cm for a 433 MHz radio remote control, for example. And for a smartphone that uses the GSM radio frequency of 900 MHz, the optimum antenna length is 8.3 cm.

Fortunately, there are various ways of miniaturizing the antennas using a special shape or electrical components. However, the more an antenna deviates from the optimum length, the greater the losses and therefore the lower the efficiency and radio range.

1) Directional antenna for radio measurements, 2) Antenna integrated in the layout, 3) Helix antenna, 4) Patch antenna, 5) Rod antennas

Directional antennas

A special characteristic of every antenna is the direction of radiation. A vertical rod antenna, for example, radiates the radio waves optimally 360° horizontally. On the other hand, hardly any radio waves are emitted downwards or upwards. Such a rod antenna can be compared with a rod lamp, which also radiates the light equally well 360° all around. The entire light is thus distributed across the room. The radio wave energy is also distributed all around a rod antenna.

If you now want to concentrate all the energy in a certain direction, as is the case with a car headlight, for example, there are so-called directional antennas. These antennas radiate the radio waves preferentially in one direction and thus achieve a greater radio range in this direction. In theory, this directional effect is referred to as GAIN and is specified in the unit [dBi]. The higher this dBi value, the more directional effect an antenna has.

In order to develop an optimum antenna for a specific application, it is therefore important to know whether the radio system only needs to work well in one direction or all around.

Difference between the range of a directional antenna and a rod antenna.

What influence does a housing have on the antenna

There are different housing materials such as plastic, wood, metal, etc. In some cases, the electronics and therefore also the antenna are even covered with a synthetic resin casting compound. What influence do these materials have on the efficiency of the antenna?

Basically, the housing material and thus the influence on the antenna can be divided into two types.

• With housings made of electrically conductive material such as metal, the radio waves of the antenna are practically completely blocked. The efficiency of the antenna drops to a minimum and therefore the antenna must be mounted outside the housing in order to achieve maximum range.
• Although housings made of non-electrically conductive materials such as plastic or wood can affect an antenna, it is normally possible to compensate for this almost completely by adjusting the antenna accordingly. The radio waves are only minimally attenuated and therefore the antenna can easily be "hidden" in the housing, as the antenna efficiency is hardly affected.

In terms of radio technology, housing materials that are electrically non-conductive are therefore preferable. This means that the antenna can normally be hidden inside the housing and is therefore invisible to the user.

Why does "Schmidiger Funklösungen" attach great importance to good antenna efficiency?

Antennas that are too small or not optimally tuned often achieve a poor efficiency of < 25%. Good efficiency has two very decisive positive effects!

• The radio range can be increased
• Increase the battery life of the transmitter

The radiated transmission power is limited by various standards. If a transmitter wants to radiate the maximum permitted transmission power for maximum radio range, the transmitter must supply a certain power to the antenna. If the antenna has poor efficiency, the power supplied must be increased accordingly in order to achieve the maximum radiated power again. This additional transmission power required can reduce the battery life of battery-operated transmitters accordingly.

Each receiver has a technically limited sensitivity. The less signal power is lost due to the efficiency of the antenna, the more signal power is fed to the receiver. Accordingly, a receiver with an optimum antenna can receive absolutely weaker radio signals and therefore clearly achieve a greater radio range.

In order to achieve the maximum radio range and also the longest possible battery life, the antenna efficiency must be optimized to the maximum.

"We deal with antenna optimization practically every day. Accordingly, we have all the necessary measuring equipment and extensive know-how to achieve the best possible antenna efficiency and therefore the best possible radio range. We would be happy to support you with our knowledge for your next radio project."