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how to increase the efficiency - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.

 Post subject: how to increase the efficiency
Posted: Tue Sep 02, 2008 11:02 pm 
User avatar

Joined: Fri Dec 14, 2007 11:23 am
Posts: 9
Location: malaysia
i have design monopole antenna for 915mhz
however the efficiency only 38.7%. so many ways i have done and
change other design but i can't improve the efficiency.

i have limitation size for gnd plane and also size for monopole antenna
what should i do?please help me


 Post subject:
Posted: Wed Sep 03, 2008 9:30 am 
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 236
Location: London UK
Hello lee
How are you measuring the efficiency?
What are you using as a comparison reference to define 100% efficiency?
What gain, polarization and bandwidth do you need?

 Post subject:
Posted: Wed Sep 03, 2008 11:06 pm 
User avatar

Joined: Fri Dec 14, 2007 11:23 am
Posts: 9
Location: malaysia
1. i measure the efficiency using the chamber

2. what do u mean comparison reference to define 100%

3. the gain 1dB it is linear polarization and the bandwidth 25MHz

 Post subject:
Posted: Thu Sep 04, 2008 7:00 am 
User avatar

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 236
Location: London UK
Hi lee
The 1dB gain, linear polar and the 25MHz (about 2.5%) bandwidth are all achievable with a variety of designs, such as normal mode helical quarter wave etc.
It was just you used the term "efficiency" and find that 38% is unacceptable. I wondered what your reference model is for 100% so I can see what basis you are using for acceptable performance.
When you say you are using a chamber, that does not describe the actual method. Are you plotting the E and H plane far-field patterns and integrating them in software as part of a suite, like Scientific Atlanta or similar, then accepting the given answer? Or are you comparing the radiated power with the input power to the antenna and computing the answer as a percentage?
As a rule of thumb, the ground-plane dimensions (critical for compact antennas) should be about lambda/3 by lambda/3 at least in order to achieve high efficiency. Anything smaller will greatly reduce the efficiency.
Have you checked the reflection coefficient and/or S parameters?

Posted  11/12/2012
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