阿基赛马螺旋天线参数

Archimedean螺旋天线可以归类为frequency-independent antenna从某种意义上说，在整个带宽中，其输入阻抗和增益几乎保持恒定。在低频率下，辐射区位于螺旋的最外部，同时在高频处，它在中心附近。因此，螺旋天线的最低截止频率与其外半径有关，最高的截止频率与其内半径有关。这意味着天线的带宽可能非常大，仅取决于尺寸和打印精度。以下是给出的螺旋的尺寸[1]在米中。

Ro = 50e-3; Ri = 5.5e-3; turns = 4;

Create and View Archimedean Spiral Antenna

Create an Archimedean spiral antenna using the parameters defined.

sp = spiralarchimedean（'Turns',turns,“ Innerradius”,Ri,'OuterRadius',Ro); figure; show(sp);

Impedance Behavior of Archimedean Spiral Antenna

The impedance behavior of the spiral antenna shows multiple resonances at the low frequency band, before achieving a relatively constant resistance and reactance behavior. To capture these resonances we split the entire frequency band into two subbands. In the lower-frequency band, we sample with a finer spacing, while at the higher frequencies we opt for coarser spacing.

NF1 = 20;NF2 = 6;fband1 = linspace（0.8e9,1.4e9，nf1）;fband2 = linspace（1.4e9,2.5e9，nf2）;freq = unique（[Fband1，fband2]）;图;阻抗（SP，FREQ）；

Reflection Coefficient

可以使用Booker的Babinet原理扩展补充结构的原理[2]，可以获得该螺旋天线的输入阻抗。对于自由空间中的天线，其输入阻抗等于60 $$\pi$$= 188.5 $$\omega$$。该值非常接近在上面所见图中较高频率下观察到的阻抗的值。反射系数使用188的参考阻抗计算 $$\omega$$。From the plot below it is seen that the present antenna is well matched for frequencies higher than 1.1 GHz.

S = sparameters (sp,频率,188);图;rfplot(年代);标题（'Reflection Coefficient'）；

This matched frequency is higher than the approximate theoretical result of 0.96 GHz [1] since the current still reaches spiral tips as seen in the computational figure that follows.

Current Distribution

The surface current distribution at low frequencies is:

图;current(sp, 0.85e9); view(0,90);

At higher frequencies, surface currents decay long before reaching the spiral tips. This results in a better matching.

图;current(sp, 1.9e9); view(0,90);

轴向比

The current distribution presents a 180-degree rotational symmetry, which produces a circularly polarized radiated wave. The plot below shows the axial ratio at broadside of the spiral antenna. Observe that the spiral antenna achieves a good circular polarization for frequencies higher than 1.4 GHz.

freq = 0.8e9:100e6:2.5e9; AR = zeros(size(freq));form=1:numel(freq) AR(m) = axialRatio(sp, freq(m), 0, 90);end图;plot(freq, AR); grid上;轴（[0.8E9 2.5E9 0 10]）;Xlabel（'Frequency (Hz)'）；ylabel('Axial ratio (dB)'）；标题（'Axial Ratio of Archimedean Spiral Antenna at Boresight'）；

Discussion on the Results

论文[1]designs an Archimedean spiral antenna and compares its performance to theoretical results as well as to the commercially available EM solvers. The results obtained using the Antenna Toolbox™ match very well with the results presented in [1].

Reference

[1]以色列Hinostroza，“概念de Reseaux大型天线螺旋螺旋”，其他，Supelec，2013年，2013年，第58-62页。在线网址：https://tel.archives-ouvertes.fr/file/index/docid/830469/filename/Hinostroza_Israel_final_final_thesis_2013.pdf

[2] C. A. Balanis, Antenna Theory. Analysis and Design, Wiley, New York, 3rd Edition, 2005.