Title: Deployment isolation guideline
MOTOROLA INDIA LIMITED
Deployment isolation Guidelines for GSM 900 /1800 systems
Motorola India Limited, CIG, Delhi 415/2, Mehrauli Gurgaon Road Sector 14, Gurgaon Haryana-122001 INDIA
Summary: This document describes the isolation required for deploying GSM 900 / 1800 antennas on the same site.
4/11/2017
1
Title: Deployment isolation guideline Antenna As more and more network operator convert their network into dualband, many antenna vendors have introduced their product to support the dualband deployment. The antenna support on dualband still focused on combination of GSM900 and GSM1800 frequency band. In term of field implementations, there are combinations of antennas, which can be installed for dualband sites as pictured below. The picture assumed that the GSM900 and GSM1800 are co-located. The first possibility is that each frequency has its own antenna physically separated. In this configuration, each antenna has it's own dedicated feeder. This is the advantage when antenna placement requirement for GSM900 and
Figure 1 Simplified antenna implementation. The left side is using two antennas physically separated. Combiner is used in one end. On the right side, diplexer used for real dualband antenna.
GSM1800 is different, for instance on top of the building or on a mast where GSM1800 antenna required having different heights over GSM900. As it offers a fully independent configuration for each frequency band, the cost regarding the additional feeder needs to be considered.The second option is where two antennas for different frequency bands are actually put together in one antenna enclosure. In this configuration dedicated feeders for each frequency band are still used. This can be use where the design requirement is very limiting. Possible variant of this antenna is that each antenna within the enclosure has its own electrical antenna tilt. As the antenna have feeders for each frequency band, consideration about cost should be also taken into account as well as the size of this antenna, which is slightly bigger than normal antenna.he third option is the real dualband antenna. This antenna incorporates
Fig ure 2. Several options of antenna types that can be installed in the dualband site. Left is two single frequency antennas for each band, middle is actually two antennas placed in one enclosure, and right is the real dualband antenna.
4/11/2017
2
Title: Deployment isolation guideline internal diplexer so RX and TX path are combination of GSM900 and GSM1800 signals. Diplexer at the BTS side also should be installed when using this type of antenna. This antenna offers simplified installation of feeder as the signals are already combined within the feeder. Consideration should be taken into account about the cost, which is very expensive. The possibility to have separate electrical downtilt for each frequency band should be considered as well. The disadvantage of this type of antenna is that it has more limited flexibility for bore angle of the antenna. When the operator have different coverage objective for GSM900 and GSM1800, this type of antenna may not be suitable. Other variant of this type of antenna is that the electrical downtilt can be altered remotely from the OMC for example.
Isolation requirement for various antenna arrangement: Isolation with horizontal spacing:
Decoupling in dB= 22+20log(s/) - (Gt + Gr) s: spacing between antennas in feet : wavelength in inches = 11808/Freq. (MHz)
It is(GSM=30cm and DCS=15cm)
Gt: gain of transmit antenna Gr: gain of receive antenna Constraints: (s/) > 10 and Gt & Gr < 10 dB The required separation depends on antenna gain G, antenna orientation and HPBW, Thus the antenna gain G() in direction of the interfered antenna has accordingly to be taken into account in formula given below The pure horizontal separation is not recommended to provide sufficient Tx-Rx decoupling, since the antenna gain increases the required separation drastically increases. 4/11/2017
3
Title: Deployment isolation guideline
Isolation with Vertical spacing:
Decoupling in dB = 28+40 log (s/) Typically 1 < S and dBmax = 70 dB s is spacing between ends of radiating portion of antennas We have calculated the following distances above 10 feet. Horizontal spacing Distance 3m GSM 41 dB DCS 47 dB
4m 43dB 49 dB
5m 45,5 dB 51 dB
Vertical spacing Distance 0,5m GSM 35 dB DCS 47 dB
1,5m 54dB 66 dB
2,5m 63 dB 75 dB
For horizontal spacing the isolation values (with the distance between antennas is below 10) must be measured in the test range. Generally experience shows that the isolation result from calculations are pessimistic compared to our test field results. Typically vertical separation S used for GSM and DCS: S=50cm 4/11/2017
4
Title: Deployment isolation guideline
Annexure 1: Sample isolation measurements for different antenna arrangements
4/11/2017
5
Title: Deployment isolation guideline
4/11/2017
6
Title: Deployment isolation guideline
4/11/2017
7
Title: Deployment isolation guideline
4/11/2017
8
