Matching Network affecting Radiation Pattern?

[kyjackchan]

Should I expect the same radiation pattern after inserting a different matching network (MN) in front of the antenna input?
say in extreme case, if my MN and antenna produce near 'shorted' input impedance, i'd see the same radiation pattern but with an extremely low gain?

 

[flatulent]

If your transmission line does not radiate there should be no pattern shape difference. There will be more power reaching the antenna in some case compared to others and this will scale all points on the pattern by the same amount.

 

[harmony]

it would definitely affect the gain of the antenna, but not necessary the RP

 

[kyjackchan]

THx for the replies,
the reason i asked here was that given such argument, why students (and those published in many IEEE papers) are still struggling with getting a 'good return loss' for the antenna alone? why not design an antenna by simply looking at the radiation patterns and match the antenna using MN afterwards?

i could only think of the following:
1) insertion loss in the matching network,
2) bandwidth requirement,
3) cost of the matching networks (caps, inductors for <6ghz, or stubs for >6ghz)

is there any other concerns about getting a good return loss for an antenna?

 

[RFSimulator]

Hi.

Everything radiates if you use an appropriate matching network. The matching network does not affect the pattern (as long as the network does not radiate itself). The antenna can bee seen as complex impedance with real and imaginary part. The real part of this impedance corresponds to the radiated energy.

Problem is: if the impedance of the antenna is almost completely imaginary, voltage and current are almost 90 deg out of phase. In order to transmit some energy you will need very high currents and voltages. A very high fraction of you power is reactive power. This is something you would like to avoide.

F.