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Here we model and simulate a monopole antenna above a finite ground plane using AWR AXIEM.
We assume the monopole antenna is excited by a coaxial cable from below, like the geometry depicted in Figure 1.
The outside conductor of the coax connects
to the ground plane. In contrast, the coaxial cable's inside conductor does not touch the ground plane, but instead
extends well above the ground plane some distance d, forming the monopole wire antenna. The antenna resonates when d is around a quarter
of the free-space wavelength. I have divided the procedure to model and simulate the monopole in 5 basic steps below.
The video illustrating this procedure is given below.
Download this video here.
Highlights of the procedure for Step 1 are presented below.
Divide space into three layers like that shown in Figure 2. The top and bottom boundaries are set as "approx open", i.e. they are matched to free-space. The monopole antenna itself is a cylindrical via that extends between EM layers 2 and 3. The finite ground plane and ports are all defined on EM layer 3. In the middle of the finite ground plane sits a rectangle separated on all sides by the ground plane itself by a small air gap, like that shown in Figure 3. From the center of this hole extends the monopole antenna above the ground plane. Differential ports are used to excite the antenna, as shown in Figure 3. In the figure, "Port -1" means the differential grounding port relative to "Port +1". Numbering ports this way follows the convention for differential ports in AWR AXIEM.
The video below shows how to simulate the structure and plot the real and imaginary parts of the input impedance.
Download this video here.
The video below shows how to extract the LCR equivalent circuit from the EM simulation data.
Download this video here.
From the perspective of the input port, the monopole antenna acts (electrically) as an equivalent LCR series resonant load like that shown in Figure 4. This equivalence only holds near resonance (i.e. in a small bandwidth near the first resonant frequency).
Figure 5 shows how the values of the equivalent lumped L, C, and R elements are related to the EM simulated parameters. After the simulation is complete, the resonant frequency is found as the frequency in which Im(Zin)=0 (i.e. the imaginary part of the input impedance is zero). The equivalent resistance R is Re(Zin) at resonance (i.e the real part of the input impedance at the resonant frequency). The inductance L is related to the derivative of Im(Zin) with respect to frequency as shown in Figure 5. The capacitance is related to the inductance and the resonant frequency.
In case you are curious, in Figure 6 shows how to derive the relation between the inductance L and the derivative of Im(Zin) with respect to frequency.
The values of L, C, and R can be found in AWR Axiem by setting up the appropriate output equations as shown in the video above.
The video below shows how to plot the antenna patterns (both 2D and 3D antenna patterns are plotted as illustrated in Figures 7 and 8).
Download this video here.
The video below shows how to determine the directivity, gain, and radiation efficiency of the antenna using AWR AXIEM.
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In the video below I show how to set up a parameter sweep. Knowing how to setup parmeter sweeps is a crucial design skill when designing antennas and other EM devices. In this video we first parameterize the length of the monopole and sweep the length to see how the performance changes with different lengths. Then we parameterize the radius of the monopole and perform a sweep over two different parameters.
Download this video here.