Monopole Pcb Antenna For Gsm850 Gsm900 Dcs1800 Pcs1900 Application Note V1.00

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Monopole PCB Antenna for GSM850/GSM900/DCS1800/PCS1900 _ Application Note _V1.00 Smart Machine Smart Decision Document Title: Monopole PCB Antenna for GSM850/GSM900/DCS1800/PCS1900 Version: V1.00 Date: 2011-03-02 Status: Released Document Control ID: Monopole PCB Antenna for GSM850/GSM900/DCS1800/PCS1900_ Application Note_V1.00 General Notes SIMCom offers this information as a service to its users, to support application and engineering efforts that use the products designed by SIMCom. The information provided is based upon requirements specifically provided to SIMCom by the users. SIMCom has not undertaken any independent search for additional relevant information, including any information that may be in the user’s possession. Furthermore, system validation of this product designed by SIMCom within a larger electronic system remains the responsibility of the user or the user’s system integrator. All specifications supplied herein are subject to change. Copyright This document contains proprietary technical information which is the property of SIMCom Limited., copying of this document and giving it to others and the using or communication of the contents thereof, are forbidden without express authority. Offenders are liable to the payment of damages. All rights reserved in the event of grant of a patent or the registration of a utility model or design. All specification supplied herein are subject to change without notice at any time. Copyright © Shanghai SIMCom Wireless Solutions Ltd. 2011 An Hardware Design_V1.00 2 2011-03-02 Smart Machine Smart Decision Contents Contents ...........................................................................................................................................2 Figure Index ....................................................................................................................................4 Version History ...............................................................................................................................4 1 Introduction...............................................................................................................................5 2 Description of the PCB Antenna..............................................................................................5 2.1 Reason for Using Monopoly PCB Antenna .......................................................................5 2.2 Antenna Terms...................................................................................................................5 2.3 Antenna Sample Dimensions .............................................................................................6 2.4 Simulation Results .............................................................................................................7 3 Implementation Guidelines .........................................................................................................9 3.1 The Housing.....................................................................................................................10 3.2 PCB Requirements...........................................................................................................10 3.3 Antenna Placement ..........................................................................................................10 3.4 Ground Plane Size............................................................................................................11 3.5 The Trace of PCB Antenna ..............................................................................................11 3.6 General Approach to External Impedance Matching .......................................................12 4 Conclusion ..................................................................................................................................13 Contact us ......................................................................................................................................14 An Hardware Design_V1.00 3 2011-03-02 Smart Machine Smart Decision Figure Index Figure 1 Configuration of antenna sample........................................................................................6 Figure 2 Antenna sample dimensions ...............................................................................................7 Figure 3 Simulation result of return loss S11....................................................................................7 Figure 4 Simulation result of VSWR ................................................................................................8 Figure 5 Simulation 3D antenna pattern of 850MHz........................................................................8 Figure 6 Simulation 3D antenna pattern of 900MHz........................................................................8 Figure 7 Simulation 3D antenna pattern of 1800MHz......................................................................9 Figure 8 Simulation 3D antenna pattern of 1900MHz......................................................................9 Figure 9 Antenna placement ...........................................................................................................11 Figure 10 Trace impedance calculation...........................................................................................12 Figure 11 Antenna and trace are linked by a 0 Ohm resistor ..........................................................12 Figure 12 Antenna and trace are linked by pi-network ...................................................................13 Figure 13 Schematic of pi-network ...............................................................................................13 An Hardware Design_V1.00 4 2011-03-02 Smart Machine Smart Decision Version History Data Version Description of change Author 2011-03-02 V1.00 Origin Chen Shiguo An Hardware Design_V1.00 5 2011-03-02 Smart Machine Smart Decision 1 Introduction This document describes the key points about the monopole PCB antenna application design to which attention should be paid. As the monopole PCB antenna (Figure.1) can be integrated into lots of communication terminals, the application note of the antenna is described in great detail. In the application of the antenna, some irrelevant usage will lead to serious problems. In order to avoid unnecessary mistakes, this document is depicted to give customers some design guidelines. Based on such considerations, at the later sections, this document will describe some key issues that more attentions should be paid to. Some simulation results in the following content are taken out from the antenna sample, which is in ideal environment. But in customer application, the antenna’s performance could be influenced by the practical environment. This application note is intended to provide some simple guidelines/rules for using the quad-band antenna to achieve optimal performances. 2 Description of the Monopole PCB Antenna 2.1 Reason for Using Monopole PCB Antenna It is known that antenna is an important component in the communication system, which could radiate and receive RF power. Two major challenges to current antennas in communication system are wideband and low profile. The reason for wideband is more and more radio systems (such as GSM, DCS, PCS, GPS, BT/WLAN, WiMax and UWB) are going to be implemented in a single communication device, so it is very desirable to have a wideband antenna that could cover the above radio frequencies as much as possible. The reason for low-profile is that many wireless communication terminals are expected to be thinner and thinner, thus the antenna’s height has to be shorter. This indicates that a successful communication antenna should not only be wideband but also low-profile. Typical GSM antennas used for communication terminals are PIFA, PILA, and IFA. These antennas often have a certain height (a typical height of these antennas is between 5~8 mm). To achieve low-profile, different types of antenna have to be adopted. The monopole PCB antenna is the one which is low-profile, easily integrated, conveniently fabricated, and becoming more and more popular in communication systems. 2.2 Antenna Terms Antenna gain, which is a relative measurement of how much the antenna radiates or receives RF power in a given direction, compared to an isotropic radiator, measured by dBi, which An Hardware Design_V1.00 6 2011-03-02 Smart Machine Smart Decision is usually substituted by dB. A negative number means that the antenna radiates or receives less than the isotropic radiator, while a positive number means the antenna radiates or receives more than that. Return loss, which is a ratio of the reflected wave’s power at transmission line following the antenna to the incident wave’s power. The return loss is usually measured by dB, and expected to be less than -10dB in some high quality system. Voltage Standing Wave Ratio (VSWR), which is a ratio of the maximum voltage of standing wave to the minimum voltage of standing wave, and expected to be less than 2 in some high quality systems. Antenna pattern, which is the variation of the field intensity of an antenna as an angular function with respect to the axis. Efficiency, which is the radio of the power radiated to the total power supplied to the radio, and expected to be more than 40% in many systems. TRP, which stands for total radiated power. In many systems, TRP is expected to be more than 28 dBm for GSM850 or GSM900, and more than 25 dBm for DCS1800 or PCS1900. TIS, which stands for total isotropic sensitivity, and it is expected to be less than -102 dBm in many systems. 2.3 Antenna Sample Dimensions The antenna described in this document is a bent monopole. To reduce size, the antenna should be tuned on the PCB plane. The antenna is implemented on a 1 mm thick FR4 PCB substrate, and no metal is beneath the antenna. The antenna sample produced by SIMCom, as shown in Figure 1, is with the size of 70*40mm, and the sample’s particular dimensions are listed in Figure 2, whose unit is mm. In actual application, the antenna’s size could be reduced to less than 36*26mm in communication system, as shown in Figure 9. Figure 1: Configuration of antenna sample An Hardware Design_V1.00 7 2011-03-02 Smart Machine Smart Decision Figure 2: Antenna sample dimensions 2.4 Simulation Results Ansoft HFSS, which is used to design the PCB antenna, is a professional tool for the fast and accurate 3D EM simulation of high frequency problems. The simulation model of the monopole PCB antenna is consistent with the antenna sample, which is shown in figure 1. The PCB substrate material is FR4, with relative permittivity εr of 4.35 and loss tangent tanδ of 0.014. Some simulation results are listed below, the return loss S11 and VSWR is shown in Figure 3 and Figure 4 respectively, and the 3D antenna pattern of 850MHz, 900MHz, 1800MHz and 1900MHz is shown in figure 5, Figure 6, Figure 7 and Figure 8 respectively. S11 Ansoft LLC Improve3-G2 0.00 Curve Info dB(S(1,1)) Setup1 : Sw eep1 -5.00 m1 m2 m5 m3 -10.00 Name dB(S(1,1)) -15.00 -20.00 X m4 Y m1 0.8200 -6.8519 m2 0.9600 -7.4641 m3 1.7100 -10.1651 m4 1.9900 -13.1001 m5 2.1000 -9.7619 -25.00 -30.00 -35.00 -40.00 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 Freq [GHz] Figure 3: Return loss S11 An Hardware Design_V1.00 8 2011-03-02 Smart Machine Smart Decision VSWR Ansoft LLC Improve3-G2 30.00 Curve Info Name 25.00 X Y m1 0.8200 2.6655 m2 0.9600 2.4689 m3 1.7100 1.8997 m4 1.9600 1.4596 VSWR(1) Setup1 : Sw eep1 VSWR(1) 20.00 15.00 10.00 5.00 m1 m2 m3 m4 0.00 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 Freq [GHz] Figure 4: Voltage Standing Wave Ratio (VSWR) Figure 5: Simulation 3D antenna pattern of 850MHz An Hardware Design_V1.00 9 2011-03-02 Smart Machine Smart Decision Figure 6: Simulation 3D antenna pattern of 900MHz Figure 7: Simulation 3D antenna pattern of 1800MHz Figure 8: Simulation 3D antenna pattern of 1900MHz The impedance bandwidth of the antenna (S11 below -7.4dB dB level) covers the current radio system of GSM850/GSM900/DCS1800/PCS1900, which indicates that the proposed antenna would be useful for communication system. Radiation characteristics of the proposed antenna are almost omnidirectional. The antenna gain of 850MHz, 900MHz, 1800MHz and 1900MHz is above -2dBi. 3 Implementation Guidelines To achieve optimal performances of the Monopole PCB antenna, some basic regulations should be observed. 1) The housing of the antenna has to be non-metallic 2) The substrate underneath the antenna has to be appointed FR-4 PCB 3) An inhibit area has to be preserved around the antenna to make it work properly 4) An appropriate trace on the PCB has to be made to connect the monopole PCB antenna to the An Hardware Design_V1.00 10 2011-03-02 Smart Machine Smart Decision RF module 5) Basic EMC rules must in any case be followed in order to implement a PCB antenna suited for RF. 3.1 The Housing As for any internal antenna, to avoid shielding electromagnetic wave, the housing has to be non-conductive. Every plastic/dielectric material makes the antenna resonate at lower frequencies, which should be taken into account, so the antenna has to be tuned to slightly higher frequencies in application. 3.2 PCB Requirements The antenna requires FR4 material (1mm thickness) underneath it to resonate in the GSM850/GSM900 /DCS1800/PCS1900 frequency bands, so it has to be placed on a free FR4 area without any other metal as shown in figure 1. Since substrate’s relative permittivity is an important factor in dimensioning an antenna, a typical standard value in electronic manufacturing of the PCB FR4 is recommended, which is 4.35+/-0.05. The loss tangent tanδ of the PCB, which could affect the performance of the antenna, is expected to be less than 0.02. 3.3 Antenna Placement To avoid unexpected interferences, it is suggested to lay the monopole antenna in the corner of the PCB in communication terminal, and an inhibit area of not less than 10 mm width has to be preserved beside the antenna to make it work properly, such as in Figure 9. In order not to affect the antenna performance, no conductive part has to be placed closer than 10 mm from the antenna contour. To achieve optimal performance, any metal (such as ground plane, traces…) is forbidden to adhibit to FR4 PCB not only underneath the antenna, but also in the inhibited area. As for any internal antenna, it is also wise to avoid placement of components which is capable to generate radiated spurious/harmonics or to pick up radio frequency interference in the close vicinity of antenna. An Hardware Design_V1.00 11 2011-03-02 Smart Machine Smart Decision Figure 9: Antenna placement 3.4 Ground Plane Size Ground plane is a must in order to have a good EMC behavior, but in this case the ground plane is also needed as antenna’s electrical counterweight. It is suggested to use a ground plane area of at least 15mm*36mm to get optimal performance. With smaller ground plane extension, the antenna performance may be somewhat reduced, but that depends on application layout. 3.5 The Trace of PCB Antenna Because the antenna is applied in a 50ohm system, its output load impedance should be consistent to 50ohm. To meet this requirement, the RF trace should be impedance-controlled, and its characteristic impedance should be similar to 50ohm. In this scheme, the G-CPW trace is adopted, which is easily transformed to any other type of trace, and the size of the G-CPW is accounted by TXLINE 2003 in Figure 10. It should be noted that the RF trace’s size is mainly determined by the depth and relative permittivity of the PCB substrate. Since EMI problems are always severe when an internal antenna is used, a good shielding strategy is to have only short trace (which is expected to be less than 10 mm) on the outer layer and route the long traces on the internal layers, this implies the use of at least 4 layers of PCB. An Hardware Design_V1.00 12 2011-03-02 Smart Machine Smart Decision Figure 10: Trace impedance calculation 3.6 General Approach to External Impedance Matching It is advisable to introduce a discrete components matching network on the PCB, which could cope with potential impedance mismatch produced by application environment. If the trace matches well with the antenna, only a 0 Ohm resistor will be mounted, which is shown in Figure 11. Otherwise, tune the matching pi-network simply by changing components’ values, which is shown in Figure 12, and the schematic of the matching network is also shown in Figure 13. Without any further PCB layout change, the implement of matching pi-network is very easy. Figure 11: Antenna and trace are linked by a 0 Ohm resistor An Hardware Design_V1.00 13 2011-03-02 Smart Machine Smart Decision Figure 12: Antenna and trace are linked by pi-network Figure 13: Schematic of pi-network 4 Conclusion The simulation results of the monopole PCB antenna described in this note are nearly perfect for the current radio system of GSM850/GSM900/DCS1800/PCS1900, and the practical performance of the antenna is similar to the simulation results according to the designer’s experience. Besides good electronic performance, the monopole PCB antenna is low-profile, easily integrated, conveniently fabricated. It is believed that the PCB antenna recommended by SIMCom would provide a great help for the customer application in antenna design. An Hardware Design_V1.00 14 2011-03-02 Smart Machine Smart Decision Contact us: Shanghai SIMCom Wireless Solutions Ltd Add: SIM Technology Building A, No. 633, Jinzhong Road, Shanghai, P. R. China 200335 Tel: +86 21 3252 3130 Fax: +86 21 3252 3020 URL: www.sim.com An Hardware Design_V1.00 15 2011-03-02