Basic product information

Taoglas' Monopole-PIFA SMD antenna "PA.710.A" is described. Antenna knowledge and design knowledge is important in optimizing RF equipment.

The PA.710.A is an inverted F antenna and does not have GND under the antenna. In addition, it is built with a rectangular ceramic substrate together with the short circuit board. The product is surface mount and supplied on tape and reel, a significant advantage to the current market.

PA.710.A can achieve high radiation performance by connecting to GND.GND size has an important role for antennas and is related to efficiency and wavelength andis more pronounced at lower frequencies. The optimal GND size on the evaluation board is 107mm x 45mm.

However, compared to other existing antenna technologies, this antenna can achieve very high reception sensitivity even with a small GND area. This application note is intended to help you understand the factors that affect antenna performance.
Taoglas recommends that designers strictly follow this application note.

best application

PA.710.A is an enhanced version of PA.25A operating at 700MHz to cover LTE. Suitable for all cellular applications such as CDMA, WCDMA, UMTS, HSPA, LTE, GSM, AMPS, GPRS. Since this antenna is SMD type, it needs to be free of metal around it to radiate.

impedance

From the RF module to the transmission line, the antenna should be designed with 50Ω. In reality, the impedance is not a perfect 50Ω on the transmitting and receiving sides. Therefore, it is important to adjust the impedance of the antenna to 50Ω.

bandwidth

The PA.710.A return loss is determined by the GND plane and the clearance around the antenna. It also has a 107mm GND plane and 13mm clearance to meet LTE bandwidth requirements. (see item 14)

A GND plane of 70 mm or more and a clearance of 20 mm are required for efficient operation of the PA.710.A.Therefore, performance may be degraded if the clearance around the antenna is not 20mm.

gain

An ideal cellular band antenna should achieve a peak gain of 0dBi for omnidirectional radiation. Small size and high efficiency can be achieved by using ceramic materials.

polarization

All Taoglas cellular and broadband antennas can very efficiently align broadcast signals from linearly polarized antennas mounted on cellular base stations.

Whether the antenna is horizontally or vertically polarized depends on the placement of the antenna. In fact, the internal antenna radiates and receives are cross-polarized due to reflections from the environment and scattering in the atmosphere.

efficiency

Antenna efficiency is the ratio of the total power fed into the antenna to the power radiated by the antenna. Mobile and portable devices ideally require isotropic radiated power with a gain of "0", so efficiency is a good indicator of the radiation characteristics of an antenna.

20% efficiency is generally sufficient for mobile devices. However, considering the use overseas, we recommend an efficiency of 40% or more. In that case, it is necessary to secure a GND plane of 70 mm or more. If the GND plane is short, the certainty of passing approval decreases. High efficiency results in lower battery consumption in weak signal areas. Therefore, efficiency is affected by multiple factors such as impedance matching, transmission power, and noise.

Effect of GND plane

In general the GND plane of the PIFA should be at least λ/4 of the lowest operating band. If it is shorter than λ/4, the antenna efficiency will be affected. This can also cause problems with radiated power.

If the GND plane is much longer than λ/4, high frequencies will be affected. Below are the efficiency results for different GND planes.

For example, if the GND plane is longer than 107mm, it can be adjusted and corrected by increasing the width of the GND plane. There is no fixed ratio for this, so it is necessary to respond according to the user's board size. Also, if the GND plane is 70mm, the antenna performance will be sufficient.

The PIFA antenna should be placed at the end of the user's board. Because the electromagnetic wave translates to the longest side of the board and amplifies the radiated power. If this placement correspondence is not implemented, antenna performance will be significantly degraded.

A large GND plane improves return loss and efficiency, but the maximum optimal length is 107mm.High efficiency applications require a width of 45mm and a minimum length of 70mm.

GND on the top layer of the PCB has a greater impact on antenna performance than GND layers on other layers. Also connect the top, middle and bottom layers with vias to strengthen the GND. These are important for coplanar transmission lines, which are discussed later.

Antennas can be placed on top and bottom layers. Other layers should be GND. If that is not possible, connect all layers with vias.

isolation

It is a coupling characteristic between two antennas that is different from isolation. For example, in the case of MIMO antennas, it is ideal to have an isolation of -10dB or more between the first and second antennas. One method is to place the polarization directions at different positions, but this is difficult with omnidirectional cellular antennas, so it is important to separate the antennas as much as possible.

About the Environment

All antennas have an impact on electrical performance when placed close to the device or enclosure. If placed in an enclosed area, it should be 20mm from GND, other devices and metal for maximum efficiency. If these clearances cannot be secured, the antenna efficiency will decrease and the tuned frequency will shift. Proximity effects also adversely affect the antenna radiation pattern. Therefore, do not use metal or EMI absorbing materials for the enclosure.

PA.710.A requires 3mm clearance around. 1mm or less is for antenna detuning andCauses the occurrence of radiation efficiency.

Superiority

(1) Can be mounted on mobile devices due to its small size and minimal footprint
(2) Can be mounted by machine
③Transmission loss is minimized and greatly improved compared to similar products
④ As long as the layout of the application note is followed, the radiation spurious is reduced compared to other antennas.
⑤High gain for both vertical and horizontal polarization
The above is very useful for wireless applications. Directivity is not defined and reflections and multipath signals can come from any plane.
An important parameter to consider at this time is the total field strength. It will be the sum of all signal vectors from all horizontal and vertical.
⑦ Guarantee high quality and yield
(8) Antenna design cost is unnecessary

coplanar transmission line

For coplanar transmission, it is from the GSM module to the GND plane edge. The edge of the GND plane to the antenna is not coplanar. Adjust this to maintain 50Ω ±10%.

The value presented here is an example, so it is actually recommended to modify it. You can get 50Ω by matching the height depending on the pair you choose.

It is recommended to put a via on the edge of the GND plane. As a result, a good GND can be secured, and a safe 50Ω can be secured as a system. It also has a shielding effect due to via. The figure below shows the arrangement of vias around the coplanar.

matching circuit

PIFA antennas are less detunable than other antennas, but tuning the matching antenna improves antenna performance. Matching PA.710.A achieves 50Ω with a 5.6nH parallel inductor and a 4.3pF series capacitor.

parts installation

The GND plane size for the entire evaluation board is 107mm x 45mm. (Maximum performance) In addition, the size of the entire antenna area is 120mm x 45mm. The antenna part is 13mm x 45mm.

Limitations

Be sure to place it below the green line in the figure below so that the GND plane does not come to the edge of the antenna.This includes GND planes as well as metals.

It is recommended to place the antenna on the short side of the rectangle with at least 5mm clearance if the device is placed on the GND edge.

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