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I see. Broad network on a narrow, tuned antenna.
Physically implementing the network with real components should be fun too.
Best of luck with your project.
A simple balun or isolation transformer would give perfect 180-degree outputs over a broad bandwidth. More complex networks are sometimes used to get 90-degree splits for single-sideband mixers or circular polarization over limited bandwidths. At 315 MHz, a small quadrature hybrid coupler would give 90-degree split outputs.
Yes. 8943. The phasing network is a two stage L-network in each path, stepping the impedance down toward an antenna that is greater than 50 ohms. Seems backwards. What you really care about is minimum S11 at port 1 and maximum S21 if the antenna is port 2. I would replace S1P with port 2. Delete 8943 ports 2 and 3, and adjust TR1 ratio so that port 2 reflects as the antenna real impedance at resonance. Best S11 and S21 should occur when the phasing/matching network is optimum.
That is a separate problem. I question the design of the network. The inductor values look very small for 315 MHz. S11 was terrible in my simulation with the dipole equivalent circuit also.
I didn’t quite say that right. I think the problem was that the two outputs from the network are not equal and opposite voltages, so you cannot ground the center of a two-part dipole model. It is the difference between the two network outputs that is important. Difference voltage, which is highest when the phases are 180 degrees apart.
The network was designed to provide a 180-degree phase difference, NOT constant +90 and -90 degrees required when you ground the middle of the dipole. Floating the dipole with the transformer fixed the problem. The minor common-mode effects of using a physical dipole without a physical transformer should not pose a problem if the network is mounted near the dipole.
It is usually good to employ a balun at the feed point of a dipole when using an unbalanced (coaxial) transmission line. With the network, you would also need a balun between the network and any coax line to the dipole. Mini-Circuits sells baluns and isolation transformers for low power (< 1 watt).
This data looks more believable. Have you looked at S11 on a finer scale: separate scale or separate graph?
Well P2 and P3 are always going to show 180 degrees apart without the ground connection in between. That is probably not useful information.
I just now noticed that you are using a bowtie dipole, which is broader bandwidth and higher feed impedance than the wire dipole model that I used. I’m not sure how practical it is to use 1-port s1p data for half of a dipole, which depends highly on the common-mode reference to something, such as a reflector screen or just the shield of the feed line. Bowtie used to be fed with 300-ohm twin lead. I don’t know how you would measure one half of the dipole that way.
You might want to download free EZNEC and simulate the bowtie. You can probably find a close example design to get started. Get s1p for the balanced feed impedance, then use an ideal 1:1 transformer in uSimmics to feed it with a balanced circuit.
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OK. It appears that you are simulating a lumped-element 180-degree power splitter to feed a dipole antenna. You might want to do a time domain (transient) simulation to be sure you are seeing what you expect. I don’t know if uSimmics will accept .S1P file in a time domain simulation. If not, substitute resistors that are close to the real part. Look at the Port 2 and Port 3 waveforms on the same graph at a few frequencies. I think you want outputs of equal amplitude and 180 degrees out of phase.
Parameter tune does not appear to support negative values.
Negative values are useful as error terms when trying to fit a circuit model to the performance of a physical circuit. i.e.: a negative capacitor in parallel with a capacitor. uSimmics does appear to simulate negative value capacitors correctly.
Thanks!
