Antenna Systems & Technology - Fall 2016 - 13

FEATURE ARTICLE While most engineers, when comparing the antenna datasheets of different antennas, might observe identical parameter values - it is important to bear in mind that the antenna which has the fewest dispersions will always be the better on in the long run. Myth 2: A Panel Antenna Has the Same Pattern as its Radiation Elements Many operators are familiar with panel antenna patterns and electrical tilting in the horizontal and vertical planes. However, there is a misperception about how the panel's overall pattern is shaped. A panel antenna comprises a number of radiating antenna elements' arrays, for high and low bands. Low band elements dipoles are larger in size, and require more isolation distances in between each other than high-band ones. It is thus, logical that more of the high-band arrays can fit into the same antenna radome. However, the panel antenna pattern is quite dissimilar from its radiating antenna element pattern. This is the result of multiplying the antenna elements and the array factor patterns. The latter's shape is based on its antenna element's spacing, phase shifts and amplitude variation - with the graph below depicting this concept. It should be noted that changing the AE's phase shifts and amplitudes results in an electrical beamforming of the array factor - and, consequently the final overall beam shape. Figure 3. Forming a panel antenna pattern Myth 3: Multiple Input Ports Mean Multiple Arrays Inside One of the most important RF planning parameters is the number of input ports and independent electrical tilt controls. Unfortunately, there is a perception held by most RF planners that buying an antenna with different connectors and separate tilt controls means more integrated antenna elements arrays inside. Low-band elements dipoles are both larger in size, and also require more isolation distances in between. In this case, if an RF planner needs to run GSM 900MHz and LTE 800MHz on separate antenna parts, this would impose doubling of the antenna width - a practice which is highly discouraged. There are several solutions that have been used in the past: Common Tilt Control One solution is to diplex the G900 and L800 signals before the antenna ports, which should be followed by a normal single-array antenna of normal width. In order to separate input ports from the outside, the diplexer can even be embedded inside the antenna radome. However, optimizers often complain about the difficulty involved in tuning both the LTE and GSM tilts separately. This lead to a better approach being developed. Separate Tilt Control: A common solution deployed by most antenna manufacturers today involves using diplexers behind each antenna element. This will cause each signal to have its own path, until it is diplexed upon reaching an AE. The technique works well for the most part, although it does involve an awareness of the PIM risks involved when diplex'ing bands on the same antenna elements. Not all bands combinations' can be safely diplexed over the same antenna elements without risking PIM. There are free resources online that allow you to calculate this more effectively. Myth 4: Multibeam Antennas Have Multiple Arrays Inside Often when asked about twin beam or multibeam antennas, the first picture that jumps to many installers' minds is a combination of two or more arrays, which are positioned to radiate in different directions. However, it isn't necessarily true that all multibeam antennas have multiple arrays inside. Article continued on page 14 www.AntennasOnline.com Fall 2016 Antenna Systems & Technology 13 http://www.AntennasOnline.com

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