Microwave Journal
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6 to 44 GHz, 45° Beamwidth Dual Polarized Antenna

May 13, 2021

A seemingly endless variety of antennas are available for 5G applications. Selecting from this range of options typically involves a complex set of choices among competing performance objectives. A new antenna from Eravant strikes a good balance for many applications that require ultra-wide bandwidth, moderate beamwidth and polarization diversity.

Model SAV-0634431050-2F-S1-QR is a quad-ridged horn antenna with dual coaxial feeds that covers 6 to 44 GHz. For each port, the typical E-plane beamwidth is 45 degrees while the H-plane beamwidth is 55 degrees (see Figure 1). Sidelobe suppression is 15 dB or better, the cross-polarization is better than -15 dB, with -20 dB or less at most frequencies and port-to-port isolation above 30 dB across most of the operating spectrum (see Figure 2).

Over the operating frequency range, the gain increases from 4 dBi at 6 GHz to 12 dBi at 44 GHz (see Figure 3). Reduced gain at lower frequencies is partially from the smaller effective aperture relative to the wavelength. Loading effects related to the antenna’s compact structure are also a factor limiting the low frequency gain, which is reflected by the lower return loss (see Figure 4).

Figure 1

Figure 1 Typical antenna patterns measured at 23 GHz.

Figure 2

Figure 2 Typical port isolation vs. frequency.

The feed ports have 2.4 mm coaxial connectors, with return loss typically around 15 dB. Power handling capability is 10 W. The antenna occupies a small volume, measuring 1.6 × 1.4 × 1.4 in. (4.1 × 3.7 × 3.7 cm), and the assembly includes a 1/4-20 threaded hole for easy attachment to a standard mount.

Figure 3

Figure 3 Typical antenna gain vs. frequency.

Figure 4

Figure 4 Simulated return loss and isolation vs. frequency.

APPLICATIONS

Figure 5

Figure 5 Dual mode, circularly polarized antenna configuration.

As a development tool, the dual polarized antenna is useful in a variety of test scenarios. In an antenna test range, the radiation patterns of a test antenna can be evaluated for vertical and horizontal polarization without requiring the operator to adjust antenna position. Adding a quadrature hybrid network, such as Eravant’s SCZ-0234031009-KFKF-43, yields a circularly polarized antenna with both right-hand circularly polarized (RHCP) and left-hand circularly polarized (LHCP) ports (see Figure 5). Arrays of antennas with this configuration can support MIMO communication systems that use environments rich in multipath propagation channels.

Dual polarized antennas can also contribute to the development of advanced radar sensors. When electrically reciprocal materials and components are used in an antenna that transmits a given polarization, the antenna is sensitive to received signals with the same polarization. This rule applies to any reciprocal antenna, regardless of polarization. To suppress co-polarized reflections, a cross-polarized (two-port) antenna system is required. Distances in confined spaces are commonly measured using a dual-port antenna that transmits and receives circularly polarized signals with orthogonal polarizations. Sidelobe responses that involve an even number of signal bounces, such as caused by container walls, are generally co-polarized relative to the transmitted signal and are suppressed by a receiver that is more sensitive to cross-polarized signals.

A radar system with cross-polarized transmit and receive channels can effectively suppress reflections from many types of background clutter that reflect co-polarized signals. Reflections from structures such as flat surfaces and trihedral corner reflectors exhibit an odd number of radar bounces, usually having adequate cross-polarized radar cross-sections. Objects having complex shapes often exhibit similar responses for both co-polarized and cross-polarized antenna configurations, making clutter identification and suppression possible. Separate transmit and receive antennas are often used to coherently receive both co-polarized and cross-polarized radar signals in various combinations. Both RHCP and LHCP signals are transmitted and received, yielding four distinct radar measurements. This arrangement enables advanced signal processing to dynamically suppress clutter-generated signals while enhancing target responses.

Figure 6

Figure 6 OMT-based, circularly polarized antenna.

Although quad-ridge horn antennas often provide low-cost solutions adequate for many situations, some applications require antennas tailored to specific levels of performance. Eravant offers hundreds of antennas, enabling system developers to find the best match for unique requirements. Many communication links depend on dual polarized antennas having high gain with low sidelobes and low levels of cross-polarization. Eravant’s family of lens-corrected and Gaussian optical, dual polarized antennas are often suitable. Offerings include at least 60 models covering the waveguide bands from 17 to 170 GHz, with gain from 22 to 48 dBi. Cross-polarization is typically better than -25 dB. Cassegrain antennas offer high gain, typically 50 dBi at frequencies from 33 to 50 GHz using reflectors with diameters of 48 in. (128 cm). They are well-suited for many long-distance communication links and radar sensors. For applications requiring exceptional cross-polarization, low sidelobes and flat gain, Eravant has many dual polarized, waveguide horn antennas fed using orthomode transducers (OMT). Cross-polarization and port isolation are typically 40 dB or better, with gain from 10 to 50 dBi (see Figure 6).

Eravant carries a comprehensive selection of antennas to serve many applications in instrumentation, communication, radar and remote sensing, with frequency coverage spanning the entire 5G spectrum, well into THz.

Eravant
Torrance, Calif.
www.eravant.com