about harmonic ?help

Why the matching of antenna affect the harmonic ?
Any body can tell me the reason ?

best regards !

1. Load impedance influence gain (see Microwave Transistor Amplifiers, Gonzalez, Prentice Hall)
2. Antenna gain tends to increase with frequency (disregarding matching, especially if you use non-resonant antenna like small loop for ISM applications) - this is only imporatant if your measure radiated signal

Regards
D.

Hello,

1. If you match the antenna impedance at the fundamental frequency. Harmonic will be reduced due to mismatch at harmonic frequency.

2. Are you connecting the antenna to output of PA? The load impedance of PA can determine the harmonic power. Since the antenna and the matching network can affect the load of PA. Therefore the antenna matching can affect the harmonics

eecly

No , antenna connect to the switchplexer. then to PA output .Could you please give me some advice for improve harmanic ?

Best regads!

but for the GSM 2nd harmonic (1.8G ) is just for the DCS band , how can I maka mismatch for 2nd harmonic. Anybody can provide some advice ? best regards

Hi,

I assume you are designing ASM for dual band phones. You are right, it is not easy to reduce the second harmonic content. One way is to include it in switchplexer (diplexer+swich).

I assume you have antenna port on one side and GSM/DCS ends of diplexer/antenna switch-plexer. Then you connect each GSM and DCS sides to Rx/Tx switch to choose the mode of operation

You can design antenn-diplexer to have isolation between GSM/DCS branches. This will improve automatically the suppression of second harmonic of GSM falling on DCS frequency.

flyhigh

In dual band GSM, to reduce the radiated 2nd harmonic on GSM900 you have to have first of all a very low conducted 2nd harmonic at antenna connector, on this band (after LPF, switch, diplexer, etc). Usually lower level than spec requirement.
The topology of the antenna matching network affect the harmonics. For example a low pass topology it helps reducing the radiated harmonics.

regards

Recently ,I found a question . When I added a match network on DCS band, the conducted spurious ( GSM 2n harmonic :1.8G ) got very bad. the diffence is 10dbm with the no match companent on DCS band. Aay body could give some advice?

Best regards!

mckinson:

how many dBc of 2nd harmonic of GSM with and without matching?

Do you mean with matching at DCS track, the 2nd harmonic at GSM band (which is 1.8GHz) is 10dB higer?

If that's what you mean, it is due to good matching at DCS track improve the impedance matching and output power. With higher output power, the inteference to GSM second harmonic will be greater.

I explained this in some of your post on this, but you did not reply me...
I can further comment on this if you let me more details...

mckinson: here is the post http://www.elektroda.pl/eboard/ftopic65391-30.html

read my comments and reply me so that I can know more details...