Versatile PCS/DCS Patch Antennas
Cushcraft Corp. Manchester, NH
Today's personal communications service (PCS) and digital communications system (DCS) operators need to expand coverage and capacity while controlling infrastructure costs. The microcells, picocells and repeaters require a low cost, high performance antenna to provide concentrated coverage for PCS and DCS applications. A new family of antennas that employs patch technology meets these requirements. The DirectLink series antennas use MicroAir air dielectric technology for increased efficiency without the usual reliance on etched substrates. The brass antenna elements are secured by a contemporary-style, injection-molded enclosure.
The Antenna Design
The technology used in the design and fabrication of DirectLink antennas is based on the principle that a substrate of low dielectric constant and three-dimensional microstrip transitions can ensure wideband SWR and gain performance for microstrip antennas. The antennas consist of a single patch (no parasitic elements) suspended over a ground plane at a height corresponding to the required bandwidth. One of the patch edges is connected to the feeding cable through a three-dimensional transition that acts as a wide probe. This wide probe's design is critical in shape and location since it must perform as a transmission line with no radiation. A post connecting the patch to the ground plane ensures mechanical support for the patch. The strategic location of the post corresponds to a low voltage point on the patch. Since the diameter of the post is less than one-tenth of the smallest dimension of the patch, no significant impact on the input impedance is observed. Similarly, where the dielectric/metallic post is larger in diameter, the shape of the patch is modified to compensate. Several designs were implemented and tested. Some of these antennas exhibit extremely wideband characteristics relative to traditional single-patch antennas built on dielectric substrates. The widest bandwidth (SWR = 2) was 100 percent. In addition to the electrical performance advantages, this technology solves several long-standing problems associated with traditional microstrip antenna designs. The antenna supports greater changes in temperature since there is no dielectric with its characteristic temperature coefficient of expansion, which differs from that of the metallization. The efficiency is considerably higher since there are no dielectric and surface wave losses typically associated with thick dielectric substrate patch antennas. The antennas also can handle significantly higher average and peak power levels.
The Mechanical Structure
Part of the design effort was to develop an antenna that would be easy to install with flexible installation options and reliable performance in an outdoor environment. In addition, production material and labor costs must be minimized to keep the selling price low. To accomplish these goals, injection-molded parts were utilized. The DirectLink antennas offer six unique injection-molded parts, two of which compose the main housing and are common to the entire family of antennas. The other parts are utilized in the standard wall-mount and ±30° articulating bracket versions. Both the wall mount and the articulating bracket are interchangeable with the antenna housing. The main housing is designed and constructed such that all of the internal antenna components are positioned and supported by the housing itself. This technique reduces assembly time and cost, and ensures repeatability in manufacturing. In addition, the housing's construction provides a self-sealing, weather-resistant joint between the individual injection-molded pieces. The antenna's MicroAir technology coupled with the injection-molded housing make the completed antenna suitable for quick and reliable assembly in a production line environment.
DirectLink antennas are available at frequencies from 1710 to 1880 MHz for use in the DCS band, 1850 to 1990 for use in the PCS band and 2300 to 2400 MHz for use in the industrial, scientific and medical (ISM) band. Models are also available that operate at 5150 to 5350 MHz and 5725 to 5825 MHz. The antennas feature a gain of 7.5 dB (12 dB for the 5 GHz versions). Polarization is linear and power handling is 50 W (25 W at 5 GHz). The 3 dB E- and H-plane beamwidths are 60° and 85° (DCS), 55° and 80° (PCS), and 50° and 65° (ISM), respectively. Figure 1 shows the radiation patterns for the three antenna types. All antennas display a front-to-back ratio of 12 dB and SWR of 1.5. Figure 2 shows SWR vs. frequency for the DCS and PCS versions. RF connectors are SMA or TNC with other types available on request. The articulating and nonarticulating wall-mount versions weigh 8 and 5 oz, respectively. Mast-mount kits are available, as well as custom mounting configurations for high volume applications. Figure 3 shows an outline drawing of the standard wall-mount antenna.
DirectLink antennas can be used in low and high tier microcells and picocells in PCS and DCS wireless services, including wireless local loop systems. Additional applications include wireless local area networks and wireless private branch exchange services. Installations requiring directional antenna performance, ease of installation and pleasing aesthetics are also applicable. An engineering evaluation kit is available, as shown in Figure 4 . The kit includes the DirectLink antenna; standard wall-mount, articulating wall-mount, universal wall-/mast-mount and mast-mount options; instruction sheets; a DirectLink brochure; a registration card; and a diskette containing engineering data. The versatility of five mounting options ensures that the mounting configuration that best matches the RF environment for the particular location is selected. Engineering kits are available immediately. Specific antenna price and delivery information are available upon request.
Cushcraft Corp., Manchester, NH (800) 258-3860.