|
|
From
yesterday’s technology comes the technology
of tomorrow.
Mitsubishi Materials antenna technology is answering
the call for “just in time”.
|
|
| Radio waves are waves produced by the interaction
of time -varying electric and magnetic fields. More
properly they are referred to as electromagnetic waves.
With the Wireless Telegraphy Act it was decided that
all electromagnetic waves with a frequency below 3,000GHz
would be called radio waves. |
| An antenna converts electrical energy to radio waves
and transmits them into the sky as well as collecting
radio waves from the sky and converting them to electrical
energy. |
|
|
As antenna serves as the electrical power conversion device between a circuit and the air, the keys to it’s efficiency are as follows:
|
|
(1) |
Input characteristics with the contact point on the circuit side |
|
(2) |
Radiation characteristics from the contact point to the air |
| Input characteristics |
|
Electric power is supplied efficiently to the antenna without reflecting back into the circuit at the feeding point
> If the impedance between the antenna and the feed line is not matched correctly, the signal will reflect back and no power will be supplied to the antenna. |
| Radiation characteristics |
|
The power supplied to the antenna is not lost within the antenna but is transmitted as a radio wave.
> If the antenna is made of high loss material (conductors and dielectrics), then the power that was supplied to the antenna will be dissipated into heat and lost. |
|
|
The Characteristics of a general antenna are shown below.
| (1) Input Characteristics |
|
| Frequency - Return loss chart … |
where the return loss is low, indicates that the antenna is well matched at that frequency. |
| Frequency – VSWR chart … … |
In the same way, a low value shows a good matching of the antenna. |
* Bandwidth … The antenna is good to the extent of good matching and the width of the frequency domain.
Here, where the matched area is good … the frequency domain will have a VSWR value of less than 3 (return loss is less than –6.02dB). |
|
| (2) Radiation Characteristics |
|
| Radiation pattern … |
The strength of the antenna emission is displayed.
It shows that antennas emit well in their projected direction.
It is usually displayed in three planes (XY, YZ and ZX planes).
|
| Gain [dBd] … … |
Given as a ratio to a standard antenna (half wave dipole).
Usually displayed as the average of the three planes (XY, YZ and ZX planes).
Designated as a combination of the vertical and horizontal polarity power gains.
|
|
|
|
Because many things, such as the board shape,
surrounding
components
and
the
case
covering the board, can affect the Characteristics of an
antenna,
most designs require customization of
the
antenna
to compensate for the shift in Characteristics. Correcting
the
shift in the Characteristics
of
the
antenna is known as tuning. For this work, having lots of
experience from adjusting many items
and
equipment
is where an antenna maker can really show their strengths.
This experience can really help the user in getting the help
needed for a quick product design.
 |
|
 |
|
 |
Receipt of customers board |
|
 |
|
| (1) |
Mount standard part on board and check for shift in
Characteristics |
| (2) |
Select an item from the frequency and impedance series
to correct the shift in Characteristics |
| (3) |
Mount the new part on the board and check Characteristics.
Repeat steps 2 and 3 if necessary to get the best results |
|
 |
 |
Measure the radiation pattern in the company’s anechoic chamber.
Check the center frequency, upper and lower band limits as well as verify the gain.
|
 |
|
 |
Send the customer a technical report of the test results and recommendation for the part to use. |
|
 |
(1) We have anticipated the characteristic shifts and created a series of parts that match those shifts and corrects them.
• Frequency Series Parts
When an antenna is mounted, the center frequency will shift due to surrounding elements. These parts will bring that frequency back to the proper center frequency. There are 18 values available in 29MHz steps.
• Impendence Series Parts
The impedance of an antenna will appear different depending on the shape of the board and other items surrounding the antenna. Normally in these situations, designers will make a matching circuit by adding capacitors or inductors, we however have created antennas with 3 different inpedance values, so a standard antenna can be quickly matched to the design without any modifications to the circuit.
(2) Complete Measurement Environment
Our facilites are complete with a full anechoic chamber and all required test equipment for quick and complete testing.
(3) Standard Data Reporting
Using standardized data forms, the information can quickly be assembled into a report.
* If a verbal reply is sufficient, we can reply within 2 days of receiving the customer’s board.
|
It is important to select the correct antenna for the application.
1) Important Information about Small Antennas!
As for chip antennas, you must consider the ground plane surrounding the
area the chip is mounted. When using a small antenna it is often necessary to
make a large ground plan to improve the characteristics of the antenna, the results
is a larger area on the board for the antenna. Also, since small antennas typically
are lambda/4 type antennas, a large GND is also important. In fact if the GND
is not large enough, there are some small antennas that will not operate.
> We consider the ground plane area in addition to the area for mounting antenna as a set, and can propose the optimum configuration for both.
Also, if there is room in your design, the larger antenna you can use the better off you will be. (It has been theoretically proven that as an antenna becomes smaller the performance deteriorates.)
2) Use Directivity Appropriately!
When you know the direction of the transmission, you should choose to use a directional antenna. If you don’t, you will scatter the radio waves and the power will be wasted.
Also,
as seen in the recent case with SAR, directional antennas
were best to effectively isolate the body.
> We have both directional and omni directional antennas, so please consider what are best for your application.
3) Pitfall of Broadband Antennas!
For return loss characteristics, the loss amount is a combination of the
transmission power and the power lost. Even in the case where the power loss
is great and there is no transmission at all, the antenna may be seen as having
very good broadband ■ Characteristics. To best judge the band, the
gain’s frequency characteristics should be judged.
> The standard data we submit then is the average gain for the necessary frequency.
4) Losses for the Matching Circuit!
This circuit is used to match the impedance at the feed of the antenna. In actuality, this circuit is also the primary cause of power loss. In addition, this circuit takes up additional space on the board, adding to the total area required for the antenna. If however, the antenna’s impedance is matched with the characteristic impedance from the beginning, there is no need for this circuit.
> We do not use matching circuits, but instead have the ability to tune the antenna to match the impedance.
|
|
|
|
