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Compact Broadband Antenna Integrated with Filter

Akademische Arbeit 2019 39 Seiten

Elektrotechnik

Leseprobe

Contents

Abstract

List of Figures

List of Tables

Abbreviations

1 Introduction
1.1 Antenna for Wireless Application
1.2 Filters for Wireless Application
1.3 Design Consideration Parameters of MSA
1.3.1 Substrate Properties
1.3.2 Resonant Element Length
1.3.3 Resonant Input Resistance
1.3.4 Bandwidth
1.3.5 Losses due to Surface Waves
1.3.6 Losses due to Dielectric
1.3.7 Losses due to Dispersion
1.4 Parameters of MSA
1.4.1 Effect of Width (W)
1.4.2 Effect of Dielectric Constant
1.4.3 Effect of Height (h)
1.4.4 Effect of Loss Tangent
1.4.5 Effect of Probe Diameter
1.4.6 Effect of Feed Point Location (x)
1.4.7 Effect of Radome
1.4.8 Effect of Ground Plane
1.5 Introduction to the Problem

2 Related Literature Review

3 Parametric Study of MSA
3.1 Design Consideration Parameters of MSA
3.1.1 Substrate Properties
3.1.2 Resonant Element Length
3.1.3 Resonant Input Resistance
3.1.4 Bandwidth
3.1.5 Losses due to Surface Waves
3.1.6 Losses due to Dielectric
3.1.7 Losses due to Dispersion
3.2 Parameters of MSA
3.2.1 Effect of Width (W)
3.2.2 Effect of Dielectric Constant
3.2.3 Effect of Height (h)
3.2.4 Effect of Loss Tangent
3.2.5 Effect of Probe Diameter
3.2.6 Effect of Feed Point Location (x)
3.2.7 Effect of Radome
3.2.8 Effect of Ground Plane

4 Remarks and Conclusions
4.1 Remarks
4.2 Conclusions

Bibliography

Abstract

In recent years, there has been constant growth in using gigahertz frequencies for various applications. The state of the art of antenna integration with passive circuits techniques offering increased cut-off frequencies, open up new opportunities for integrating systems along with an antenna for either Transmit/Receive application. The work carried out in this seminar mainly deals with the survey of antenna structures which are compatible to integrate with passive circuits for microwave as well as milimeter/sub-milimeter wave applications. Lot of research in the field of passive receiver frontend design is being carried out. This work covers three aspects of passive receiver frontend design. The first is the analysis and design of new wideband high gain microstrip antennas, the second aspect is the design of compact high performance low-pass and band-pass filters and the third aspects is to integrate antenna and filter into single substrate. The trend of communication systems has imposed many restrictions on designers to have systems which should be light weight, robustness and have easy integration to other microwave circuits. In most of the communications systems the receiving antenna is followed with a bandpass filter. In microwave band this is normally a distributed filter and is implemented using the transmission line resonators. The transmission line filters are not compact, and in many applications where size is an issue may not provide the best solution. In the new active arrays, for example, it is desirable to integrate a complete front end with each individual antenna element. The area allocated to each cell, however, is determined by the array design and apertures efficiency requirements and is barely integrate the antenna and band pass filter in a single module, as is it more compact may also decrease the pre-filtering losses to improve the noise performance. The design of such system is a challenging task.

List of Figures

1.1 Resonant length versus height for (1) E r =2.55, W =0.3 λ ; (2) E r =12.8, W =0.15 λ

1.2 Input resistances versus height

1.3 Bandwidth versus height

1.4 Dielectric slabs & its mode

1.5 Efficiency versus height

3.1 Resonant length versus height for (1) E r =2.55, W =0.3 λ ; (2) E r =12.8, W =0.15 λ

3.2 Input resistances versus height

3.3 Bandwidth versus height

3.4 Dielectric slabs & its mode

3.5 Efficiency versus height

List of Tables

1.1 Electrical properties of commonly used substrate materials for MSAs

2.1 Antennas Used in Commercial Wireless Systems

3.1 Electrical properties of commonly used substrate materials for MSAs

Abbreviations

Abbildung in dieser Leseprobe nicht enthalten

Chapter 1

Introduction

1.1 Antenna for Wireless Application

Definition: A metallic apparatus for sending and receiving electromagnetic waves. In other words the antenna is the transitional structure between free-space and a guiding device. It is used to transport electromagnetic energy from the transmitting source to the antenna, or from the antenna to the receiver. In the former case, we have a transmitting antenna and in the latter a receiving antenna. For wireless communication systems, the antenna is one of the most critical components. A good design of the antenna can relax system requirements and improve overall system performance [6].

1.2 Filters for Wireless Application

Electronic filters are circuits that have signal processing functions. i.e. they transform an input signal to obtain an output signal with the required characteristics. In the frequency domain filters are used to reject unwanted signal frequencies and to pass signals of desired frequencies. Filters are indispensable devices, in many systems and applications including wireless broadband, mobile, and satellite communications, radar, navigation, sensing and other systems. With the development of these systems, mostly induced by great commercial interests, limited electromagnetic spectrum has to be shared among more and more systems. Thus, there is an increasing demand for RF, microwave, and millimetre wave filters with more stringent requirements. These filters are employed in various systems to select or confine signals within specified spectral limits [15].

1.3 Design Consideration Parameters of MSA

The design of the microstrip antennas (MSA) is critical at higher frequencies due to a number of factors. For example, conventional microstrip antennas at lower frequencies use thin substrates and generally have narrow bandwidth performance. One method of improving the bandwidth is to use a thicker substrate. Therefore, as these substrates would be electrically thick at higher frequencies, one would expect a higher bandwidth, but at the same time the losses would increase and hence must be compensated. In addition, as the substrate thickness is increased, higher order surface-wave modes may propagate. The following characteristics must be considered while designing the microstrip antenna elements at higher frequencies.

- Substrate properties
- Resonant element length
- Resonant input resistance
- Bandwidth
- Losses due to surface waves
- Losses due to dielectric
- Dispersion effect

1.3.1 Substrate Properties

The most commonly used substrate materials are Unreinforced Poly Tetra Fluoro Ethylene (PTFE), Teflon, Reinforced PTFE, RT Duriod 5880, Fused Quartz, 96% Alumina etc. Electrical properties of these materials are summarized in the Table. The data are at X-band (8-12 GHz) and room temperature. However, the data are reasonably accurate for millimeter wave microstrip antenna design. The main reason for this is that, the dependence of dielectric constant on frequency is known to be low, especially for frequencies ranges of up to 110 GHz, where microstrip antennas are typically being used.

Abbildung in dieser Leseprobe nicht enthalten

Table 1.1: Electrical properties of commonly used substrate materials for MSAs

Substrate selection for a microstrip antenna design is guided by the following criterion:

- Effects of dispersion on the dielectric constant and loss tangent of the substrate;
- Magnitude of copper and dielectric losses;
- Possibility of surface wave excitation;
- Anisotropy, if any, in the substrate;
- Environmental concerns, such as the effects of temperature, humidity
- Cost

1.3.2 Resonant Element Length

One of the considerations in the design of a rectangular microstrip antenna is the length L (radius r in case of circular MSA) for desired resonant frequency. This length is a function of substrate thickness h and dielectric constant r, and in case of a RMSA element, a function of width W. Because the dielectric fills only part of the region surrounding the antenna element, the resonant length does not scale with dielectric constant as an antenna in a homogeneous medium would.

Figure Represents variation of resonant length for the first resonance of a printed rectangular microstrip patch element versus substrate thickness h for two different substrates. The patch width is W = 0.3 λ (λ is the free space wavelength). The performance of microstrip antenna element deteriorates for substrate thickness approximately 0.1 0 due to inductive input impedance locus. This effect occurs for both probe type and microstrip line type feeds. This situation is undesirable in most cases, and so the use of patches

Abbildung in dieser Leseprobe nicht enthalten

Figure 1.1: Resonant length versus height for (1) E r =2.55, W =0.3 λ ; (2) E r =12.8, W =0.15 λ

on thick substrates may not be practical unless some way of countering this inductive trend, by using capacitive gap coupling from a feed line, for example, is used.

1.3.3 Resonant Input Resistance

Abbildung in dieser Leseprobe nicht enthalten

Figure 1.2: Input resistances versus height

Figure shows the input resistance of a Microstrip patch for the two substrates versus thickness. As previously mentioned, the Microstrip antenna element performance becomes worse for h 0.1 λ. The patch resistance shown in figure for h 0.1 λ is the real part of the input impedance for a patch length of 0.27 λ.

1.3.4 Bandwidth

The impedance bandwidth of the MSA is defined as the frequency range over which it is matched with that of the feed line. This bandwidth is usually specified for voltage standing wave ratio (VSWR) less than 2. Sometimes for stringent applications, VSWR requirement is specified to be less than 1.5.

Abbildung in dieser Leseprobe nicht enthalten

Figure 1.3: Bandwidth versus height

Figure shows the calculated bandwidth of a MSA versus substrate thickness for a PTFE substrate. The patch width is 0.3 0 and is fed by a probe at a point L/4 from the patch edge, although the feeding method or position does not affect the intrinsic patch bandwidth. The bandwidth increase rapidly with increasing substrate thickness, so that bandwidths of 10 to 20% can be obtained for substrate thickness in the range of h = 0.1 λ to 0.2 λ.

1.3.5 Losses due to Surface Waves

Two types of surface wave modes are possible, transverse magnetic (TM) and transverse electric (TE). For both types, the field components would vary sinusoidal with z in the substrate, and decrease exponentially in the z direction outside the substrate, where the various axes are shown in figure.

In general, the mode spectrum of a grounded dielectric slab contains both TE and TM modes, as shown in figure. The interval between the cut-off frequencies of two surface wave modes is given by

Abbildung in dieser Leseprobe nicht enthalten

Figure 1.4: Dielectric slabs & its mode

Abbildung in dieser Leseprobe nicht enthalten

As the TM0 mode has a zero cut-off frequency, this mode is always present in the substrate, regardless of the values of the substrate height and dielectric constant. For this mode, the y-component of the electric is strong, especially if the substrate is electrically thick or has a high dielectric constant. This characteristic affects the performance of both the single element and arrays. The higher order surface wave modes can be made non-propagating by choosing low values for h and r. Low values of h and r also help in reducing the magnitude of the TM0 mode to an acceptably low level. The price one pays for using low r is increased antenna size, while the price for using too low a value of h is possible reduction in antenna band width and radiation efficiency and thus a trade off is required.

1.3.6 Losses due to Dielectric

Power losses due to dielectric heating can be calculated by using the loss tangent and complex permittivity for the particular dielectric materials. Efficiency based on dielectric loss for a microstrip patch versus h is shown in figure.

1.3.7 Losses due to Dispersion

The dependence of the dielectric constant and loss tangent of the substrate on frequency leads to dispersion. For most dielectric materials of interest to the microstrip antenna designer, the dielectric constant decreases and the loss tangent increases with increasing frequency. The changes in the loss tangent are much more noticeable than changes in the dielectric constant, especially for frequencies up to 110 GHZ, which is the range of application of microstrip antenna.

Abbildung in dieser Leseprobe nicht enthalten

Figure 1.5: Efficiency versus height

1.4 Parameters of MSA

1.4.1 Effect of Width (W)

- Feed point location shifts towards the edge.
- Directivity increases, Area increases hence gain increases, Efficiency increases, Bandwidth increases.
- No change observed in the E-Plane but H-Plane decreases by 5%
- Resonant frequency slightly shifts downwards.
- If the width increases too much the higher order modes gets excited.

1.4.2 Effect of Dielectric Constant

- Good opportunity to reduce the size of the antenna.
- Resonant frequency shifts towards the upper side.
- Bandwidth and the gain decreases thus overall efficiency decreases.
- Feed point location shifts away from the edge. If dielectric constant decreases towards 1.0 the size of patch increases hence fringing fields and gain increases.

1.4.3 Effect of Height (h)

- Bandwidth increases directivity marginally increases.
- Resonant frequency shifts downwards.
- The height can be increased upto certain level after that efficiency decreases due to cross polarization level and surface waves.

1.4.4 Effect of Loss Tangent

- Substrate having low dielectric losses are expensive when loss tangent increases the dielectric loss increases which reduces the input impedance so feed point is shifted towards edge.
- Efficiency and gain decreases.
- No effect on resonant frequency and directivity.

1.4.5 Effect of Probe Diameter

- Generally SMA TNC and N-type connectors are used, as the probe diameter increases the probe inductance decreases hence input impedance decreases and resonant frequency slightly increases.
- No effect on gain and the directivity of the antenna.

1.4.6 Effect of Feed Point Location (x)

- If feed point is shifted from center towards edge impedance also increases, with the help of smith chart it is proved, resonant frequency slightly increases.

1.4.7 Effect of Radome

- Some times MSA is covered with a dielectric layer to protect them from the environment or some time radome material with some air gap is present with the MSA the following things are observed.
- Resonant frequency shifted downwards due to increase in effective dielectric constant.
- The bandwidth increases.

1.4.8 Effect of Ground Plane

Two types of ground plane are considered for MSA Finite and Infinite Plane. For the finite ground plane the resonant frequency is almost same but input impedance is slightly higher than that of infinite ground plane. Also for the finite ground plane the back lobes are present.

- MNM is the only method to analyze the infinite ground plane.
- The simulation time is reduced with infinite ground plane.

1.5 Introduction to the Problem

The trend of communication systems has imposed many restrictions on designers to have systems which should be light weight, robustness and have easy integration to other microwave circuits. In most of the communications systems the receiving antenna is followed with a bandpass filter. In microwave band this is normally a distributed filter and is implemented using the transmission line resonators. The transmission line filters are not compact, and in many applications where size is an issue may not provide the best solution. In the new active arrays, for example, it is desirable to integrate a complete front end with each individual antenna element. The area allocated to each cell, however, is determined by the array design and apertures efficiency requirements and is barely integrate the antenna and band pass filter in a single module, as is it more compact may also decrease the pre-filtering losses to improve the noise performance.

[...]

Details

Seiten
39
Jahr
2019
ISBN (eBook)
9783668965904
ISBN (Buch)
9783668965911
Sprache
Englisch
Katalognummer
v462115
Note
M. Tech
Schlagworte
compact broadband antenna integrated filter

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Titel: Compact Broadband Antenna Integrated with Filter