ifelix
Member level 1
good antenna rl
Hi guys,
I'm searching for someone that can once and for all give me the right way to measure antenna RL and gain. Now...I'm not interested in the method...I know it but the correct setup. I mean..when I want to measure RL of a small antenna, take as an example a little folded monopole on a little PCB (30 mm x 30 mm area) operating in the 868 MHz band or also a GSM antenna on a PCB; when I heard about RL measurement I've found: take the VNA, connect it to antenna and measure...
BUT...if I take my small PCB antenna and I connect the VNA trought a coax cable placing an SMA connector on the feed point of the antenna I won't found absolutely correct results...the problem is always and always the effect of the cable on the antenna; the dual effect: the cable that acts as a reflector of the incident field radiated by the antenna and the active radiation due to the current flowing on the external face of the coax due to the unbalanced connection of cable to the antenna.
I've found a lot of papers discussing the problem: they say, use a lambda/4 balun which inhibits the presence of the cable wrt the antenna....is this true? Do I need always to use a balun when I measure the performance of my little PCB antennas? It's obvious that if I place the SMA connector on the feed point of the antenna, its presence will affect antenna impedance and so Return Loss and also Gain!!
I've tried more times to take different measures of antenna parameters using a piece of minicoax soldered to antenna feed point and to the other end connected to VNa , or also a semirigid coax with external face soldered to ground plane, but I've found always that the presence of the cable and its orientation affects antenna performance.
Look at the picture attached: this a typical antenna I measure; the red arrow indicates the feed point where i connect the SMA connector by means I connect antenna to VNA. The diameter of the PCB is 35 mm and the antenna operates at 868 MHz. what should be the right way to measure RL and Gain? Now I'm using a coax cable on which I've placed some ferrites along it to mitigate the cable effect but this not enough:the end of the cable towards antenna and the SMA connector still deviates the real antenna performance. Is there another method to make the measurement? How can I do?
Thanks in adv to anyone which will help me!
Bye!
Hi guys,
I'm searching for someone that can once and for all give me the right way to measure antenna RL and gain. Now...I'm not interested in the method...I know it but the correct setup. I mean..when I want to measure RL of a small antenna, take as an example a little folded monopole on a little PCB (30 mm x 30 mm area) operating in the 868 MHz band or also a GSM antenna on a PCB; when I heard about RL measurement I've found: take the VNA, connect it to antenna and measure...
BUT...if I take my small PCB antenna and I connect the VNA trought a coax cable placing an SMA connector on the feed point of the antenna I won't found absolutely correct results...the problem is always and always the effect of the cable on the antenna; the dual effect: the cable that acts as a reflector of the incident field radiated by the antenna and the active radiation due to the current flowing on the external face of the coax due to the unbalanced connection of cable to the antenna.
I've found a lot of papers discussing the problem: they say, use a lambda/4 balun which inhibits the presence of the cable wrt the antenna....is this true? Do I need always to use a balun when I measure the performance of my little PCB antennas? It's obvious that if I place the SMA connector on the feed point of the antenna, its presence will affect antenna impedance and so Return Loss and also Gain!!
I've tried more times to take different measures of antenna parameters using a piece of minicoax soldered to antenna feed point and to the other end connected to VNa , or also a semirigid coax with external face soldered to ground plane, but I've found always that the presence of the cable and its orientation affects antenna performance.
Look at the picture attached: this a typical antenna I measure; the red arrow indicates the feed point where i connect the SMA connector by means I connect antenna to VNA. The diameter of the PCB is 35 mm and the antenna operates at 868 MHz. what should be the right way to measure RL and Gain? Now I'm using a coax cable on which I've placed some ferrites along it to mitigate the cable effect but this not enough:the end of the cable towards antenna and the SMA connector still deviates the real antenna performance. Is there another method to make the measurement? How can I do?
Thanks in adv to anyone which will help me!
Bye!