The dual polarized antenna is widely used in the industry due to its versatile characteristics. It is well known that the dual polarized antenna can support linear, elliptical, and circular polarized waveforms. Here are several application scenarios.
- Receiving Mode
- When the antenna receives a linearly polarized vertical waveform, only the vertical port can receive it.
- When the antenna receives a linearly polarized horizontal waveform, only the horizontal port can receive it.
- When the antenna receives an elliptical or circular polarized waveform, both the vertical and horizontal ports can receive it. There will be a 90-degree phase lagging or advancing between the ports depending on the left-hand polarization (LHP) or the right-hand polarization (RHP) of the waveform. The signal amplitudes from the ports will be the same if the waveform is perfectly circular polarized. By using the proper (90-degree) hybrid coupler, the circular or elliptical waveform can be restored.
- Transmitting Mode
- When the antenna is fed by a vertical port, the vertical linearly polarized waveform is transmitted.
- When the antenna is fed by a horizontal port, the horizontal linearly polarized waveform is transmitted.
- When the antenna is fed by the 90-degree phase difference, equal amplitude signals to the vertical and the horizontal ports, the LHP or RHP waveform is transmitted depending on the phase lagging or advancing between two signals. If the amplitude of the signals for two ports is not equal, the elliptical polarized waveform is transmitted.
- Transceiving Mode
- When the antenna is used in transmitting and receiving mode it is known as a diplexer, transmitting vertical and receiving horizontal in communication systems, for example.
SAGE Millimeter offers two standard dual polarized antenna families, namely, quad-ridge based and orthomode transducer (OMT) based. The examples of the images of the quad-ridge based antennas and the OMT based antennas are shown in Figure 1 and Figure 2, respectively.
The pros and cons of these two types of antennas are shown in Table 1. In general, the quad-ridge based antennas cover broader operating bandwidth, often more than octave, such as 2 to 18 GHz and 4 to 24 GHz and is limited to the lower millimeter-wave frequency due to stringent machining and assembly boundaries. In addition, performance wise its gain, beamwidth, sidelobes and cross-pol/port isolation etc. are limited compared to its counterpart the OMT based antennas. The main drawback of the OMT based antenna is its operating bandwidth being limited to waveguide operating bandwidths.
Table 1. Dual Polarized Antenna Comparisons
|Item||Quad-ridge Based||OMT Based|
|Antenna Type||Circular or rectangular horn||All types|
|Operating Bandwidth||Ultra-broad, such as 2 to 18 GHz||Waveguide bandwidth in general|
|Gain||Low in general, such as 10 to 20 dBi||Wide range, 10 to 50 dBi|
|Side Lobe Levels||High, 10 to 20 dBi||Wide range, antenna type dependent|
|Beamwidth||Limited range||Wide range, antenna type dependent|
|Crosspol||Low, 25 dB typical||High, 40 dB typical|
|Port isolation||Low, 20 dB typical||High, 40 dB typical|
|Port Type||Coax||Waveguide or Coax|
Due to the limitations of the quad-ridge based dual polarized antennas, the OMT based antennas draw more application attention. By selecting various antenna types such as the conical horn, pyramid horn, lens corrected, scalar horn, choke flange horn, Gaussian antenna and dish etc., one can obtains various antennas to suit any system applications. However, the antenna port of SAGE Millimeter’s standard full waveguide OMTs are equipped with square waveguides. In order to making the direct connection between the standard circular waveguide interfaced antennas and the OMTs, a mode transition is introduced. SAGE Millimeter also offers the transitions as standard components as add-on elements to convert the antenna port of the OMTs to the circular waveguide, which can be seen on its product page.
Table 2 gives an overview of the OMT-based antennas, which shall help in understanding how various OMT based dual antennas can be readily configured by using the standard catalog modes from SAGE Millimeter.
Table 2. OMT-Based Dual Polarized Antennas Overview
|Dual Polarized Antenna Types||Features|
|OMT + Conical Horn (SAC Series)||Full waveguide band performance, gain is limited to 25 dBi, high side lobe level, lower cost|
|OMT + Pyramid Horn (SAR Series)||Full waveguide band performance, gain is limited to 25 dBi, high side lobe level, lower cost|
|OMT + Choke Flange Horn (SAH Series)||Full waveguide band performance, broader beamwidth and low gain, low side lobe level, lower cross-polarization, moderate cost|
|OMT + Scalar Feed Horn (SAF Series)||Full waveguide band performance, broader beamwidth and gain up to 17 dBi, low side lobe level, lower cross-polarization, moderate cost|
|OMT + Lens Corrected Horn (SAL Series)||Full waveguide band performance, narrow beamwidth and high gain depending on the dish size selection, low side lobes, moderate cost|
|OMT + Gaussian Antenna (SAG Series)||Full waveguide band performance, narrow beamwidth and high gain depending on the aperture size selection, low side lobes, lower cross-polarization, high cost|
|OMT + Cassegrain Antenna (SAY Series)||Full waveguide band performance, narrow beamwidth and high gain depending on the dish size selected, lower cross-polarization, high cost|