New Active Dual-band Antennas for Satellite Communication
By Arsen Melconian, VP Engineering and Fayez Nima, Antenna Engineer, TECOM Industries

The usage of satellite networks for business applications is expanding, with systems such as Iridium, Globalstar and Thuraya satellite networks. These systems are rapidly gaining customer acceptance and new, more sophisticated applications are emerging, including Asset Tracking.

The fundamental concept is to use the existing satellite infrastructure to track assets (shipping containers, cars, trucks, etc.) as they move from one location to another. Collected information can be as simple as location information to more complex data gathering applications. Currently, there is a market demand for commercially available, compact, low-cost transmit and receive antennas for automobiles, boats, remote stations, and other fixed and mobile assets.

Often, in order to improve the system performance, a G/T (Gain to Noise Temperature) low noise amplifier (LNA) is needed in the path of the received signal. Integrating the LNA at the bottom of the antenna to minimize the losses between the receiving aperture and the front end of the LNA yields higher G/T. To use a common transmit and receive module on a wider range of wireless communication applications, a power amplifier (PA) is required to post the transmitted signal power in any system that uses a longer coax cable between the transmitter and the antenna. Designing a transmit and receive antenna with LNA (or LNA and PA) integration in a compact package, maintaining low cost and uncompromised performance integrity is a major challenge for antenna manufacturers.

Recently, TECOM Industries introduced a new line of active and passive antennas specifically designed to address land mobile, marine and fixed site applications. This new line provides several key technical innovations and eliminates the challenges associated with classical antenna development and design.

For example, microstrip patch design techniques are used to develop a high performance dual band antenna. These antennas transmit at L-band and receive at S-band. In these applications, a microwave substrate is used to fabricate this microstrip patch. The dielectric constant and the thickness of this substrate was selected as a trade-off between aperture gain, bandwidth and physical size. Typical performance for these antennas will have an aperture gain greater than 3.5 dBic at zenith and average gain greater than 0.0 dBic. For improved performance, an LNA is connected at the bottom of the microstrip patch, the LNA parameters (gain and noise figure) are configured to achieve minimum G/T > -30 dB/K. This provides excellent downlink performance over the S-band operating frequencies.

In many applications, a longer coaxial cable run between the tx/rx electronics and the antenna is needed. In order to keep the tx/rx module common for all applications, integration of a power amplifier into the antenna package is necessary. For these applications, the gain and power output of this PA is configured for average transmit EIRP > 29 dBm.

As with most full duplex operations, the isolation parameter between transmit and receive is crucial for the integrity of the communication system. Adding an LNA and PA module to the antenna in one compact package makes the isolation problem even more challenging. To address this, a new diplexing technique is used to achieve isolation > 45 dB between the bands. With the proper board layout and partitioning between the LNA and PA, further enhancement in the isolation is achieved.

One drawback for the microstrip (patch) antenna is its inherent gain roll-off, especially at low elevation angles. In many wireless communication applications, a slower gain variation versus the elevation angle is required to close the link. For these types of applications, a quadrifilar helix (QFH) radiating element will be implemented instead of the microstrip patch. By controlling the helical design parameters for a QFH, the antenna designer has the flexibility of shaping beam width, front to back ratio, and the spatial gain distribution. In addition, special design and layout considerations are made to minimize network losses. Mismatch and ohmic losses are very crucial to establish an efficient QFH radiating element and therefore, better average gain. The choice of the material and the type of feeding network impacts losses that should be kept to lowest possible.

As satellite communication-based industries continue to advance, new antenna techniques will be required to maintain highly efficient and compact active antennas in order to accomplish global connectivity at a low cost. Tecom Industries continues to develop new designs and technologies that are at the forefront of today’s communication needs and demands.

About Tecom
TECOM Industries, Inc., an ISO-9001 and AS-9100 company, is headquartered in Thousand Oaks, CA. Established in 1971, the company designs and manufactures antennas and antenna systems for the aerospace, military, SATCOM and commercial wireless markets. The company’s expanse of field-proven antenna solutions includes embedded, phased array, gimbaled, data link, wrap-around and broadband designs.

TECOM INDUSTRIES
www.tecom-ind.com
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