Designing dual band impedance matching network for an antenna

[pragash]

I’m a PHD student. I’m looking to design dual band filter or impedance matching network for an antenna. This impedance transformer or matching has to be lumped components. I have measured S2p file for the antenna. Can anybody let know if there is any method to use Agilent ADS to do dual band matching? So far i have come across single band matching using "impedance matching utility" and "filter design guide". I want specifically dual band matching. For example, GSM850 and GSM1900 matching design.

 

[vfone]

Before thinking to a dual-band matching network have to make the antenna to resonate at both desire frequencies.
If the antenna resonate well at both frequencies, in most cases provides good VSWR (or S11) at those frequencies, and making easier the design the matching network.
Sometimes don't even need a matching network in this situation, if the return loss is better than -10dB (VSWR 2:1).
Going directly to design a matching network for a non-resonant antenna, gives a low antenna efficiency.

 

[pragash]

Before thinking to a dual-band matching network have to make the antenna to resonate at both desire frequencies.
If the antenna resonate well at both frequencies, in most cases provides good VSWR (or S11) at those frequencies, and making easier the design the matching network.
Sometimes don't even need a matching network in this situation, if the return loss is better than -10dB (VSWR 2:1).
Going directly to design a matching network for a non-resonant antenna, gives a low antenna efficiency.

dear sir,
yes the antenna is resonating well at GSM850 and GSM1900. the return loss is -10dB and below for both band. Two reasons why im having matching network is to improve the bandwidth at GSM850 as the -10dB returnloss bandwidth is narrow, 30MHz. Target is to achieve 70MHz. second reason is to attenuate harmonics at 3GHz and above.

this matching network also should not screw up good match at GSM1900. im experienced in ADS, just checking if im missing anything there!! is there dual band matching technique available in ADS?

 

[E Kafeman]

If you have a measured s11 file for the antenna, import it in AnTune, which is a very simple tool for this kind of job.
Free download at https://www.antune.net.

 

[volker@muehlhaus]

matching network is to improve the bandwidth at GSM850 as the -10dB returnloss bandwidth is narrow, 30MHz. Target is to achieve 70MHz.

The matching network can't improve the antenna bandwidth. You need to modify the antenna itself.

 

[E Kafeman]

The matching network can't improve the antenna bandwidth.

Do the antenna design correct, and no matching is needed was previously my opinion. Was mainly working with fixed external antennas.

For an embedded cellphone antenna, is that not an relevant opinion, but these did not exist then.
Started develop embedded antennas in late 90s.
Correct used is impedance matching a part of the embedded antenna solution. Even if antenna impedance alone is rather extreme can antenna and matching network together result in relative good antenna performance.

In a smartphone, there is not space enough, there is not height enough to make a conventional antenna structure with VSWR below 1:10 in 5 or more world-wide 2/3/4G bands and with efficiency above 40% in all bands.
It was many years ago it was possible to implement a dual band PIFA in a cellphone.
When I design a multiband cellphone antenna, I must admit that I sometimes not even know antenna impedance until afterwards, when complete solution antenna+matching network design is finished.
Focus at development phase is for best efficiency for actual frequency range, do not care anything at all about antenna impedance as I use a software that constantly add a optimized virtual network during design process.
My instruments shows resulting efficiency and impedance for antenna+network as that is what I am going to implement in the smartphone.

Not really any complex antenna design, but at https://www.antune.net/demo/bluetooth/index.html do I match an BT/WiFi antenna where antenna structure alone have a VSWR 1:50 as best. That is no bandwidth at all. Antenna size is 1*7 mm and with 1 mm isolation from ground.
Final antenna+matching network had a measured efficiency around 45% for a bandwidth covering 2400-2500 MHz with VSWR below 1:3.