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4. L. Besser and R. Gilmore, Practical RF Circuit Design for Modern Wireless Systems, Volume I: Passive Circuits and Systems, Artech House Inc., Norwood, MA, 2003.

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9. B.G. Goldberg, "Miniature Radio-sensor Antenna Primer," Avaak Inc. White Paper.

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San Diego, CA

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Home > Books > Progress in Compact Antennas

Miniature Antenna with Frequency Agility

Submitted: 11 September 2013 Published: 10 September 2014

DOI: 10.5772/58838

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Progress in Compact Antennas

Edited by Laure Huitema

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Author Information

• University of Limoges, Xlim Laboratory, France

T. Monediere

*Address all correspondence to:

1. Introduction

The need of both mobility and communication leads to the integration of antennas in miniature devices so far non-connected (particularly in medical areas). The dedicated volume for the antenna, including its ground plane, has to be kept at its acceptable minimum, involving low bandwidth. Moreover, due to their poor impedance bandwidth, small antennas tend to be very sensitive to the environment. Indeed, they are directly affected by their immediate surroundings, which disturb their working band, their radiation and their performances [ 1 ]. To counter the low bandwidth of the antenna and to adapt it to variable conditions and surroundings, it can integrate active components.

Thus, active components become highly suitable for the development of modern wireless communications. Indeed, they allow the miniaturization, shifting the antenna working frequency to be matched over a wide bandwidth by covering only the user channel and the adaptation of antennas to variable operating conditions and surroundings. It is in this framework that authors will propose in this chapter to detail the integration of active components in antennas to be more compact, smart and integrated.

The first part will address an overview of the most common used techniques for compact antennas to become active. In this goal, active antennas state-of-the-art will be presented:

The first sub-section will present antennas integrating tunable components such as varactor diodes, MicroElectroMechanical systems (MEMS), Positive Intrinsic Negative (PIN) diode and Field Effect Transistor (FET).

The second sub-section will focus on active antennas using tunable materials properties, i.e. ferroelectric materials and liquid crystal.

A second part will show relevant parameters for active antennas studies. It will exhibit both challenges and how to integrate active components in order to maximize the antenna performances and efficiency. This part will be supported by concrete examples. Therefore, depending on their intended applications, readers will be prepared to find the best trade-offs between the agility method, the miniaturization and antenna performances.

The last part will be dedicated to present limitations of actual and most common solutions proposed for active and compact antennas. In this framework, new approaches will be detailed to overcome these physical limitations.

2. Overview of compact active antennas

Very small size antennas are needed for future dense wireless network deployment, for example in WBAN (Wireless Body Area Network) where the size is limited to dimensions much smaller (hearing aid, implants) than wavelength (λ 0 =12.2 cm at 2.45GHz) or for the DVB-H (Digital Video Broadcasting – Handheld) application, where the miniaturization aspect is even more critical because it is a low frequency standard (λ 0 =60 cm at 470 MHz). Therefore, the antenna has to be carefully optimized with trading off fundamental size limitations with its characteristics (especially bandwidth and efficiency). In addition, the environment of miniature antennas will be highly variable resulting in large antenna impedance and propagation channel changes. Several challenges have to be addressed. One of them is the adaptive antenna technology for compensating both low bandwidths and detuning effects.

The most commonly cited performance criterion is the achievable frequency tuning range (TR) defined as:

T R ( % ) = 2 ( f max − f min ) f max + f min .100 where f max and f min are respectively the upper and the lower antenna operating frequency. The frequency tuning can either be continuous or discrete. The continuous frequency tuning is able to continuously cover each channel of a same standard while the discrete frequency tuning can only switch between different standards. This part will present the most common methods to target frequency tunable antennas design.

2.1. Integration of active components

2.1.1. varactor diodes.

For continuous frequency tuning, the integration of varactor diodes within an antenna is the most common approach [ 2 - 5 ]. P. Bhartia et al. were the first to publish antenna integrating varactor diodes [ 6 ]. Indeed, they presented a microstrip patch antenna with varactor diodes at the edges of the structure, as illustrated Figure 1 . Both rectangular and circular tunable patches were studied, results reveal that 22% and 30% of bandwidth can respectively be achieved by varying the DC-bias-voltage between 0V and 30V.

Patch antenna integrating varactor diodes [ 28 ]

Slot antennas are also good candidates for the frequency agility [ 7 - 9 ]. N. Behdad and K. Sarabandi presented in [ 9 ] a dual band reconfigurable slot antenna. The schematic of its proposed dual-band slot antenna is shown in Figure 2 . Matching is performed by choosing appropriately the location of the microstrip feed and the length of the open circuited line.

Dual reconfigurable slot antenna [ 9 ]

Figure 3 shows the simulated and measured dual-band responses of the antenna where by applying the appropriate combination of bias voltages (V 1 and V 2 ) the frequency of the first band is kept fixed and that of the second band is tuned. Similarly, as shown in Figure 3 , it is possible to keep the frequency of the second band stationary and sweep the frequency of the first band.

Measured |S 11 | parameters for different combination of bias voltages [ 9 ]

Another example show a 3D Inverted F Antenna [ 10 ] designed to cover the entire DVB-H band going from 470 MHz to 862 MHz. To be integrated in a mobile handheld device, the antenna allocated volume had to be very compact. A good trade-off between small sizes and the impedance bandwidth was to choose a structure based on the IFA design. Indeed, the radiating monopole of this kind of structure can be folded all around a material to become more compact (see Figure 4 ).

Inverted F Antenna design (a). Antenna top view (b) [ 10 ]

However, the more compact the antenna is, the lowest the bandwidth is becoming. To counter this issue, it has been proved that using a magneto-dielectric material rather than a dielectric one allows enhancing the input impedance bandwidth. Basing on this antenna design, the idea was to integrate a varactor diode to tune the impedance matching all over the DVB-H band (see Figure 5 ).

Design integrating both magneto-dielectric material and a varactor diode [ 10 ]

A prototype of the tunable antenna has been realized ( Figure 6 ) and measured. For the diode polarization, a DC bias Tee is optimized with SMD components and measured on the DVB-H band ( Figure 6 ). After being validated, it is integrated upstream from the antenna structure as shown Figure 6 . In order to improve the quality and the reliability of wireless links, the final mobile device is integrating two antennas (see Figure 6 ) for diversity operations.

DC bias Tee with SMD components and its integration upstream from the antenna (a), integration of two antennas in the tablet dedicated to the DVB-H reception (b) [ 10 ]

Figure 7 presents respectively the variation of the input impedances and |S 11 | parameters of the antenna versus frequency for different values of the varactor diode bias voltages.

Measured input impedances (a) and |S 11 | parameters (b) for several DC bias voltages [ 10 ]

Therefore, the antenna working band is continuously tuned all over the whole DVB-H band. In the worst case, i.e. for a 2V DC bias voltage, the antenna is matched with |S 11 | <-6dB in a bandwidth which is covering more than one channel of the DVB-H band at-6 dB (largely suitable for the DVB-H standard).

2.1.2. Positive Intrinsic Negative (PIN) diodes

PIN diodes are using as switches:

The ON state of the diode can be modelled by a zero resistance, i.e. a continuous metal strip across the slot where the diode is integrated.

The OFF state of the diode can be modelled as an infinite resistance. The radiating length after the diode is not seen from RF point of view. The effective length of the antenna, and hence its operating frequency, is changing compared with the ON state case.

Selected antenna’s types for integrating PIN diodes are often slot antennas or printed antennas (e.g. printed monopole, Inverted F Antenna, …). J-M. Laheurte presented in [ 11 ] a slot antenna including pin diodes for multi-frequency operation within a frequency octave.

Switchable slot antenna including eight pin diodes [ 11 ]

As shown Figure 8 , this antenna integrates eight PIN diodes and according to their ON or OFF states combination, the antenna can operate at different and discrete frequency bands (see Figure 9 ). Instantaneous impedance bandwidths are between 8% and 21% depending on the diodes’ states combination.

Measured |S 11 | parameters for different states of diodes: all diodes OFF (i), diodes 1, 8 ON (ii), diodes 1, 2, 7, 8 ON (iii) and diodes 1, 2, 3, 6, 7, 8 ON (iv) [ 11 ]

Eventually, this antenna presents somewhat large dimensions since its main size is higher than à λ 0 /2 at 2.8 GHz. The literature presents smaller antennas integrating PIN diodes since their main size are lower than à λ 0 /2 at the working frequency [ 12 ].

Peroulis et al. [ 13 ] presented a tunable single-fed S-shaped slot loaded with a series of four PIN diodes. The effective length modification allows this antenna to operate in one of four selectable frequency bands between 530 and 890 MHz.

Before directly studying the tunable slot antenna, both single S-shaped slot antenna and PIN diodes were separately presented and studied. By this way, the issue related to the design of a suitable PIN switch has been grasped before integrate it and show its effects on the antenna performances. Indeed, to implement the electronic reconfigurability, the ideal shunt switches must be replaced by real PIN diodes. Therefore, the RF equivalent circuit of the diode has been studied (see Figure 10 ) for both the ON and OFF states. The reactive components C p and L p are modeling the packaging effect, while the others come from the electric properties of the diode junction in the ON and OFF positions. Then, the switch bias network was presented as an inductor of 470 nH and three 10 pF capacitors ( Figure 10 ).

RF equivalent circuit of the PIN diode (a) and the switch bias network (b) [ 13 ]

Finally, a reconfigurable slot antenna design ( Figure 11 ) is presented in this paper. Four switches are used in order to tune the antenna over a range of 540–950 MHz. The integration of the fours PIN diodes allows choosing the operating frequency of the antenna ( Figure 11 ).

Reconfigurable slot antenna (a) and its measured |S 11 | parameters (b) [ 13 ]

2.1.3. MicroElectroMechanical systems (MEMS)

MEMS components can allow:

Continuous frequency tuning when they are used as a variable capacitance.

Discrete frequency tuning, when they are used as switches.

E. Erdil presents in [ 14 ] a reconfigurable microstrip patch antenna integrating RF MEMS capacitor for continuously tuning the resonant frequency (see Figure 12 ). The reconfigurability of the operating frequency is obtained by loading one of the radiating edges of the microstrip patch antenna with a CPW stub on which RF MEMS bridge type capacitors are periodically placed.

Frequency tunable microstrip patch antenna integrating MEMS capacitors [ 14 ]

When a DC voltage is applied, the height of the MEMS bridges on the stub is varying, and thus the loading capacitance is also changing. Therefore, as showed Figure 13 the matching frequency around 16.05 GHz shifts down to 15.75 GHz as the actuation voltage is increased from 0 to 11.9 V, where the height of the capacitive gap changes from 1.5 μm to 1.4 μm.

|S 11 |parameters for different actuation voltages and simulation results [ 14 ]

Discrete frequency tuning can be illustrated with a reconfigurable annular slot antenna with a monolithic integration of MEMS actuators presented by B.A. Cetiner in [ 15 ]. The architecture and a photograph of the microstrip-fed reconfigurable antenna annular slot are shown in Figure 14 . The antenna has two concentric circular slots. According to MEMS switch S 1 state, they can be individually excited in order to achieve frequency reconfigurability. S 2 and S 3 switches enable the metallic annular ring, which stays between the outer and inner slots, to be shorted to RF ground.

Microstrip feeding line integrating a single-arm MEMS switch (a) and the annular slot integrating two double-arm MEMS actuators [ 15 ]

The measured |S 11 | parameters ( Figure 15 ) show that when MEMS switches are activated (down-state) by applying DC bias voltages, the antenna working band is around 5.2 GHz. Vice-versa, when MEMS switches are in the up-state, the antenna is working at 2.4 GHz.

Measured and simulated |S 11 |parameters for MEMS switches activated (5.2 GHz) and deactivated (2.4 GHz) [ 15 ]

2.1.4. Field Effect Transistor

Continuous frequency tuning can be achieved by using Field Effect Transistor. In [ 16 ], S. Kawasaki presents a slot antenna loaded with two one-port reactive FET. The electrically length of the slot is changing according to the voltage bias applying on the FET. The measured |S 11 | parameters (see Figure 16) show a 10% frequency tuning range for a gate tuning voltage (V gs ) going from 0V to-0.6V while the drain voltage (V ds ) is tuned from 0V to 0.4V.

Measured |S 11 |parameters for both gate and drain tuning voltages [ 16 ]

2.2. Agile antennas using tunable materials

Changing the material characteristics in a part of antenna designs also promise the ability to tune them in frequency. The application of a static electric field can be used to change the relative permittivity of a ferroelectric material or a liquid crystal, respectively a static magnetic field can changed the relative permeability of a ferrite. In case of printed antennas, these changes modify the effective electrical length of antennas, and then resulting in shifts of their operating frequencies.

2.2.1. Ferroelectric materials

Lead-based perovskite ceramics such as PbZr x Ti 1−x O 3 (PZT) have been the leaders, for the past 50 years, on ferroelectric material research [ 17 ] for electronic devices, sensors, actuators, and medical ultrasonic transducers, owing to their good dielectric properties over a wide temperature range. Due to health care and environmental regulations, restriction of hazardous substances as lead has been required [ 18 ]. Since the last 10 years, many efforts have been mainly devoted in the field of microwave applications to Ba x Sr 1-x TiO 3 (BST) material which is one of the most attractive materials [ 19 ] because it presents high dielectric constant, relatively low dielectric loss, interesting tunability and small temperature dependence. In fact, in BST, the Curie temperature (Tc) which defines the ferroelectric/paraelectric transition is tuned by controlling the Ba/Sr ratio. More recently some other ferroelectric ceramics such as the tantalate niobate oxide KTa x Nb 1−x O 3 (KTN) or the sodium bismuth titanate Na 0.5 Bi 0.5 TiO 3 (BNT) and its solid solutions BNT-BT are emerging.

Two different methods exist to polarize a ferroelectric material with a static electric field. A better tunability is obtained when the static electric field is perpendicular to the two electrodes. For antenna application point of view, antenna designs integrating ferroelectric materials have to move toward this kind of polarization in order to have a better reconfigurability. However, many efforts have to be devoted from realization and also simulation point of views. Therefore, compact antenna community exhibits only few papers of this kind of antennas.

V. K. Palukuru et al. [ 20 ] present a tunable antenna using an integrated ferroelectric-thick film made of BST material. The antenna is depicted in Figure 17 . It exhibits a folded slot antenna loading with a BST thin film varactor. In order to tune the dielectric permittivity of the BST film, a DC bias voltage is applied thanks to a bias-T component, which was attached to the Vector Network Analyzer. The BST varactor is placed over the radiating slot: the upper electrode (0.2 mm 0.2 mm) is part of the antenna’s metallization and the lower electrode is the antenna’s ground plane. In order to reduce the capacitance of the varactor, a slight horizontal offset is used between the electrodes. Therefore, the electric field for biasing the material is both in the vertical and the horizontal directions.

Folded slot antenna with the BST varactor (a), side cross-section (b) and top view (c) of the BST varactor [ 20 ]

The |S 11 | parameters ( Figure 18 ) show that a frequency tunability of 3.5% can be obtained with a change of the bias voltage from 0V to 200V.

Measured |S 11 |parameters for different DC-bias voltages [ 20 ]

H. Jiang presents a coplanar waveguide (CPW) square-ring slot antenna as showed Figure 19 [ 21 ]. Nine shunt ferroelectric BST thin film varactors are integrated with the CPW antenna structure achieving both antenna miniaturization and reconfiguration.

Coplanar waveguide square-ring slot antenna integrating BST material [ 21 ]

Figure 20 shows the measured |S 11 |parameter with DC bias voltages from 0 V to 7 V. Therefore the antenna working band is continuously tuned from 5.28 GHz up to 5.77 GHz.

Measured |S 11 |parameters for different DC-bias voltages [ 21 ]

2.2.2. Liquid crystal

Another technological approach for designing an agile antenna is the use of liquid crystal as a tunable dielectric. Indeed, the characterizations of liquid crystals [ 22 - 24 ] have shown that they are promising tunable materials for microwave applications, especially for operating frequencies above 10 GHz. The material features low dielectric loss and continuous tunability with low bias power consumption. The literature show that some microwave applications are using liquid crystals, e.g. for polarization agile antenna [ 25 ], tunable patch antennas [ 26 ], reflectarrays [ 27 - 28 ], filters [ 29 ], resonators [ 30 ] and variable delay lines [ 31 - 33 ].

In this framework, L. Liu presents in [ 34 ] a tunable patch antenna using a liquid crystal. Its operating frequency is around 5 GHz with a tuning range around 4% in measurement. The Figure 21 presents the antenna geometry composed of three layers of Taconic substrate. The liquid crystal is injected in the middle layer just under the microstrip patch and between the ground plane and patch top hat. A DC bias voltage was applied between the patch and ground across the liquid crystal using a bias tee at the feed input.

Tunable patch antenna using a liquid crystal [ 34 ]

The Figure 22 shows the measured return losses for the patch antenna for three states of liquid crystal bias: 0V, 5V and 10V. The 0V state reveals that the used liquid crystal without DC bias presents somewhat high losses around 0.12 for the loss tangent. Thus a 4% frequency tuning can be achieved with relatively poor radiation efficiencies, i.e. 14% at least (at 0V) to 40% (at 10V).

Measured |S 11 |parameters for different DC-bias voltages [ 34 ]

2.2.3. Ferrite materials

Frequency-tuned ferrite-based antennas are rarely presented in the literature. In [ 35 ] and [ 36 ], authors study patch antennas on ferrite substrates ( Figure 23 ) whereas A. Petosa presents in [ 37 ] a ferrite resonator antenna. In this latter, biasing of the ferrite with a static magnetic field is achieved using a permanent magnet. The magnet was located under the ferrite antenna beneath the ground plane. For a parallel magnetic-bias orientation, the resonance frequency can be tuned on 8% of bandwidth. That scales to 9% for a perpendicular magnetic-bias orientation.

Patch antenna on a ferrite substrate [ 37 ]

All results presented in the literature and investigated the properties of ferrite-based microstrip antennas indicate that factors including non-uniform bias fields and the multiple modal field distributions excited in a bulk ferrite substrate may preclude their use in practical applications.

Now that an overview of the most common used techniques for compact antennas to become active has been presented, the next part will address both challenges and how to integrate active components in order to maximize the antenna performances and efficiency.

3. Relevant parameter for frequency agile antenna studies – New approach for wireless applications.

3.1. how to integrate an active component – challenges.

To implement the reconfigurability in an antenna, the knowledge of the active component or the tunable material is essential. Even in case of commercial components, as varactor or PIN diodes, users and particularly the microwave community do not have enough parameters and information at RF frequencies. Some papers detail the integration of the RF equivalent circuit of the used component [ 10 ],[ 13 ].

The varactor diodes integrated in an antenna for frequency reconfigurability is the most popular way. Thus, this section will focus on varactor diodes issues. However, arguments can be extended to other frequency tuning methods.

In [ 10 ], the paper completes the lack of information related to most of varactor diode datasheets. Indeed, constructor only provide characteristics at low frequencies and do not give enough parameters for antenna application point of view, such as capacitance values, serial resistance and accepted power at RF frequencies. The chosen varactor in this paper has been characterized according to antenna designer criteria and its electromagnetic model has been deduced. This example is chosen in the framework of this chapter.

To correctly explain this example, the next subsection will investigate the place where the varactor can be integrated. Following the presentation of the varactor diode manufacturer’s datasheet, a complete characterization meeting antenna designer’s criteria will be explained. That will lead to the determination of the varactor diode S parameters. With the knowledge of the latter, two methods will be explained and described to reach an accurate antenna simulation and realization:

The electromagnetic equivalent circuit of the varactor diode can be deduced from the S parameters thanks to Agilent ADS.

The S parameters of the varactor diode can be directly injected in the electromagnetic simulator CST Microwave Studio ® and the antenna performances deduced thanks to a co-simulation.

3.1.1. Varactor diode area in an antenna

The varactor diode is a tunable capacitor which loads the antenna in order to artificially increase its electrical length. To be the most efficient, it must be placed where the electrical field is maximum. Take a folded Inverted F Antenna for example presented Figure 24 . The maximum of the electrical field is at the end of the radiating element (see Figure 24 ). To be integrated at this place and joined the ground plane at the same time, the varactor diode can be soldered between the ribbon and the ground. In most cases, DC-block capacitors have to be added for the varactor’s DC-bias not to be shunt.

Inverted F Antenna Measured (a) and the total electric field on the radiating element (b)

3.1.2. Varactor diode datasheet

In [ 10 ], the chosen GaAs hyperabrupt varactor diode MGV125-22 (Aeroflex Metelics) [ 38 ] has a capacity range between 0.2 pF and 2 pF for 0 to 22 Volts tuning voltage as shown Figure 25 . However, these values are given as a rough line and the datasheet does not give enough parameters for high frequencies antenna application’s point of view. Indeed, the values for junction capacitance C j ( Figure 25 ) and the quality factor Q are supplied by the manufacturer and are almost always specified at a low frequency. The Figure 25 shows the widely used varactor diode model with L p and C p the values of the package inductance and capacitance.

Manufacturer’s capacitance value (extracted at 1MHz) versus the DC bias voltage (a) and the Varactor diode model (b)

In the MGV125-22 case, junction capacitance values are specified at 1 MHz and the Q factor equals 3000 at 50 MHz for a DC bias voltage of –4 Volts. Q is defined by Q=1/(ωC j R s ). This formula can be used to calculate the series resistance R s of the varactor model at the measured frequency, its value is assumed to be constant with reverse voltage. Thus, at 50 MHz R s =1.06Ω. It is important to note that R s impacts directly the antenna total efficiency. A too high value (from 3Ω) is basically penalizing for antenna performances. This enhances the need to assess its value at microwave frequencies. For this purpose, the hyperabrupt varactor diode has to be characterized close to operating conditions (here between 470 MHz and 862 MHz).

3.1.3. Varactor diode characterization

First method: Electromagnetic model

The varactor diode is soldered on a 50 Ω impedance microstrip line as shown Figure 26 . A dedicated TRL (Through-Reflect-Line) calibration kit is manufactured ( Figure 26 ) in order to de-embed both connectors and lines. Thus S parameters of the single varactor diode can be deduced. Considering the varactor diode model previously presented in Figure 26 , C j , L p , C p and R s values can be deduced for each voltage and for a constant injected power of-10 dBm. Therefore, model component values are adjusted (see Figure 26 ) in order their S parameters to correspond with the measured ones. The Figure 26 shows the comparison between S parameters of the determined electromagnetic model (Agilent ADS) and the measured ones for 2 Volts and 10 Volts DC bias voltages.

Characterization of the varactor diode (a) and the Comparison between the electromagnetic model and the measurement on S 11 parameter on the [400 MHz – 1 GHz] frequency band (b)

These results are given as an example and the same work has been done for varactor reverse bias voltages varying from 2V to 22V with a 2V step. As expected, the corresponding electromagnetic model presents constant values according to the DC bias voltage ( Figure 27 ): L p =3.821nH, C p =0.08pF and R s =1.8Ω. The C j value presented in Figure 27 decreases as a function of DC bias voltage value.

Electromagnetic model with the capacitance values C j versus the DC bias voltage (b)

Second method: Co-simulation

Another way is to directly insert the S parameters touchstone file of the varactor diode in the antenna electromagnetic simulation as illustrated in Figure 28 .

Co-simulation of the antenna including measured S parameters of the diode

Thanks to the previous TRL calibration, only the varactor diode S parameters are inserted in the simulator. By this way, both antenna and varactor diode are combined and the S parameters of the global device can be directly simulated. An example (presented paragraph 3.3) will confirm that the two previous methods exhibit similar antenna performances.

3.2. Limitations of currently varactor diode method – Power characterization

Figure 29 provides some information regarding the accepted power by the varactor diode: high injected power involves some varactor diode distortions.

Measured S parameters according to the injected power

This figure presents S parameters of the diode for only three values of injected power:-10 dBm, 0 dBm and 10 dBm. The non-linear distortion of the diode has been studied. It reveals that the varactor diode model well fits measurements for an injected RF power lower than-5 dBm. Beyond this injected power (see for 0 dBm), no varactor model can fit the measurement. Regarding antenna’s parameters, the following example will show that a large RF power (upper than-5 dBm) involves a mismatched antenna. As far as the DVB-H application, the system is only working in receiving mode, the diode distortion will never appear and the linear electromagnetic model can be used and integrated in the electromagnetic simulator. Indeed, for receiver devices, the antenna accepted power is far lower than – 5 dBm.

3.3. Example of a basic tunable DVB-H antenna

This subsection investigates an example to show the interest of the previous varactor diode characterization. This was briefly presented in [ 4 ], it is completed here by adding the first method (electromagnetic model) and the power characterization. A basic IFA prototype loaded by the same varactor diode (see Figure 30 ) has been manufactured.

Basic IFA prototype

It has been measured for a-10 dBm RF power and its performances compared with three simulations: with both presented methods and with the varactor diode’s datasheet ( Figure 31 ). |S 11 | parameters show that both investigated methods and measurement present a good agreement. Moreover, they are different from |S 11 | parameters determined with the varactor diode datasheet. That underlines the relevance of the varactor diode characterization. Regarding the antenna total efficiency, it equals 50 % in the real case whereas it reaches 60% when the varactor datasheet is used in electromagnetic simulations.

Power characterization is illustrated on Figure 31 . This figure reminds the measured |S 11 | parameter for a power of-10 dBm. For a 10 dBm injected power, the measured |S 11 | parameter is compared with the simulated one with the second method.

|S 11 | parameters for the different methods (a) and according to the injected power (b)

There is a good agreement between the measurement and the simulation. This figure shows that the non-linearity of the varactor diode disturbs the |S 11 | parameter of the antenna. Thus, this kind of varactor diode has to be used only for reception devices.

Therefore, this section has presented how to integrate and characterize a varactor diode. It reveals the importance of the diode characterization in a design flow dedicated to antenna structure.

3.4. Discussion and trade-offs between agility techniques and physical limitations

According to the aimed application, trade-offs are necessary to design a frequency tunable antenna.

For discrete frequency tuning, PIN diodes or MEMS switches can be planed.

For continuous frequency tuning, which is often aiming for compact antennas, varactor diodes, MEMS variable capacitor and tunable materials can be used.

However, previous paragraphs have revealed that varactor diodes are not usable for transmitter devices because of their non-linearity for considering power levels.

The RF characterization of ferroelectric films shows high power handling capability [ 39 ]. Good permittivity tunability may be obtained if both materials properties and variable capacitor sizes have been properly dimensioned. The conclusion is the same for MEMS variable capacitor.

Studies on both ferroelectric material and MEMS capacitor merit extended investigations because these solutions seem to be the best and most promising alternatives faced with varactor diodes.

Performing rigorous full-wave analysis of these new components is the new challenge to extract their accurate electromagnetic models. Antennas would be optimized by considering the real response of these components. These investigations would enable the co-development of antennas integrating components’ electromagnetic models.

4. Conclusion

To conclude, an overview of compact and frequency agile antenna has been presented and detailed in this chapter while mentioning a lot of literature references. A special part has been dedicated to the presentation of the most common method to achieve a frequency tuning: the use of varactor diodes. Their integration within an antenna to be the most efficient has been shown. The study exhibits varactor diodes characterization and also reveals their limitation. A summary of the presented methods according to the intended application has been presented. Eventually, some ideas on varator diodes alternatives have been proposed in order to make antenna tunability viable for transmitter devices.

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Network sensor miniature antenna

by kachouri abdennaceur

2010, Symbolic and Numerical Methods …

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Adel Saleeb

2022, Sensors

Antennas in wireless sensor networks (WSNs) are characterized by the enhanced capacity of the network, longer range of transmission, better spatial reuse, and lower interference. In this paper, we propose a planar patch antenna for mobile communication applications operating at 1.8, 3.5, and 5.4 GHz. A planar microstrip patch antenna (MPA) consists of two F-shaped resonators that enable operations at 1.8 and 3.5 GHz while operation at 5.4 GHz is achieved when the patch is truncated from the middle. The proposed planar patch is printed on a low-cost FR-4 substrate that is 1.6 mm in thickness. The equivalent circuit model is also designed to validate the reflection coefficient of the proposed antenna with the S11 obtained from the circuit model. It contains three RLC (resistor–inductor–capacitor) circuits for generating three frequency bands for the proposed antenna. Thereby, we obtained a good agreement between simulation and measurement results. The proposed antenna has an elliptica...

Muralidhar K Bhanarkar , V. Navarkhele

2012, CUSAT, Cochi

RECTANGULAR MICROSTRIP PATCH ANTENNA FOR WIRELESS SENSOR NETWORKS 1Communication Research Laboratory, Department of Electronics, Shivaji University, Kolhapur, Maharashtra, India. Email: [email protected] 2Frequency Domain Research Laboratory, Department of Physics, Dr. BAM University, Aurangabad, Maharashtra, India. Email: [email protected] Abstract:In this paper, we mentioned the design of rectangular microstrip patch antenna andit is simulated using IE3D software. RT-duroid material is used as substrate having 2.45 permittivity with loss tangent 0.002 for the development of antenna. Paper is focused on the structure and results are obtained by simulation at 2.8GHz frequency. For the design of antenna, the coaxial feed point method was used.It is applicable for wireless sensor networks.

prudhvi raj

— In wireless communication, antenna miniaturization is a vital issue these days. This paper presents the simulation analysis of small planar antennas using different antenna miniaturization techniques. They have brought to define miniaturization methods by which we can estimate the use of micro strip antennas. Various govt. and private sector organizations made use of these techniques to solve the problem of antenna fabrication in mobiles, satellites, missiles, radar navigational aids and military applications. These techniques are used to reduce the physical size but to increase the bandwidth and efficiency of antenna. Some approaches for antenna miniaturization are introduction of slots, slits, short meandering and novel geometries like fractals or by using higher dielectrics constant. The effect of miniaturization in various antenna parameters like, radiation efficiency, gain and bandwidth are discussed. Finally the paper reports a brief description of miniaturization of antenna by using suitable and efficient methods that includes use of double layered substrate structure in microstrip patch antenna. Index Terms—micro strip patch antenna, antenna miniaturization, dielectric constant, double substrates

kachouri abdennaceur

2010, arXiv preprint arXiv:1006.0856

Ibrahim Nassar , Ibrahim T Nassar

—An electrically small meandered microstrip line antenna was investigated. The antenna was designed, fabricated and measured for an operating frequency of 2.4 GHz with a 10 dB return loss bandwidth of 2%. In order to improve the efficiency and gain, a truncated ground plane was used, and its effect on balancing the antenna currents has been studied. A Wheeler Cap was designed for the efficiency measurement and the 3-antenna method was used for measuring the gain. Ka of this antenna is 0.26, it has a gain of-0.86 dB and an efficiency of 49.7%, making it one of the efficient and high gain small antennas.

Ramesh Pokharel

2008, … , 2008. APMC 2008. …

Sudarshan Tiwari

Antenna Test & Measurement Society (ATMS)

2012, Microwave and Optical Technology Letters

David Thiel

2009, 2009 International Conference on Electromagnetics in Advanced Applications

Mubarack Ahmed

2015, Journal of Computer Science and Information Technology

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In this paper a novel design of compact microstrip antenna with impedance of 187Ω is proposed. The antenna consists of a rectangular patch with slits on the top face and a partial ground with slots at the rear end. The antenna is fabricated on FR-4 epoxy dielectric with relative permittivity of 4.4. The designed antenna has the capability of operating at 5.78GHz for wireless applications. Single element, 1x2 array and 1x4 array has been designed and it is studied that from single element design to the 1x4 array design the antenna gain has kept on increasing respectively. The proposed antenna has Omni-directional radiation pattern and it also poses a relatively excellent return loss. Radiation pattern is measured in antenna anechoic chamber. Feed line used has characteristic impedance of 50Ω. Antenna parameters such as return loss and radiation pattern show reasonable agreement with the simulated results. The antenna simulation is done using the Zeland Ie3D simulation software.

Ibrahim Nassar

In many wireless devices, antennas occupy the majority of the overall size. As compact device sizes become a greater focus in industry, the demand for small antennas escalates. In this thesis, detailed investigations on the design of a planar meandered line antenna with truncated ground plane and 3D dipole antenna at 2.4 GHz (ISM band) are presented. The primary goal of this research is to develop small, low coast, and low profile antennas for wireless sensor applications. The planar meandered line antenna was designed based on a study of different miniaturization techniques and a study of the ground plane effect. The study of the ground plane effect proved that it has a pivotal role on balancing the antenna current. The study of the miniaturization process proved that it affects directly the gain, bandwidth, and efficiency. The antenna efficiency and gain were improved using the truncated ground plane. This antenna has a measured gain of -0.86 dBi and measured efficiency of 49.7%, making it one of the efficient and high gain small antennas. The 3D dipole antenna was designed using a novel method for efficiently exploiting the available volume. This method consists of fabricating the dipole on a cube configuration with opening up the internal volume for other uses. This antenna was tested, and it was found that this antenna has good radiation characteristics according to its occupied volume. Ka of this antenna is 0.55, its measured gain is 1.69 dBi with 64.2% measured efficiency. Therefore, this design is very promising in low-power sensing applications. A Wheeler Cap was designed for measuring the efficiency and the 3- antenna method was used for measuring the designed antennas gain.

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Doaa Mohammed

— Microstrip slotted meander line antenna with diverse number of meander slots is presented for 2.4 Wireless Local Area Network (WLAN) application. The proposed antenna comprises a rectangular microstrip patch element embedded with several numbers of meander slots in many positions. The parametric study is performed to investigate the characteristic of these microstrip patch antennas with different numbers of meandered slots. Many designs of slotted meander line antenna are produced and they are analyzed based on the number of slotted meander line used. Antenna wit slotted meander lines has the most size reduction of approximately 23% of the original size. This study is an early investigation in designing the RF energy harvesting to support green technology and sustainable development particularly for Wireless Sensor Network (WSN) as well as Radio Frequency Identification (RFID) applications. Keywords— Slotted meander line antenna, microstrip patch, return loss, bandwidth, CST Studio Suite 2010.

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Antenna miniaturization has become one important research, especially in mobile communication technology development. This paper presents the development of a miniaturized antenna for RFID application (924 MHz). Meandering technique has been adopted to create a geometrically small antenna relative to its operating frequency. Measurement result shows that the fabricated antenna inherits low return loss, down to -25.915 dB. The geometry of the antenna is 25.54 mm x 16 mm, which is much smaller than its resonance wavelength (0.079? x 0.049?). The measured gain is relatively small, of about -12 dBi. Nevertheless, the obtained parameters are acceptable since the antenna is meant for near field communication application.

—In this paper, periodic structures are investigated in antenna design for wireless applications. These antennas were compared with CRLH miniaturization method. Three different models of patch antenna with coaxial feed on EBG ground, metamaterial substrate or EBG/AMC structure have been presented here. Also two compact dual-band antennas have been designed and fabricated based on CRLH techniques for wireless and GSM applications. The first antenna has directional pattern and operates at 1760, 2550 and 3850 MHz (three-band antenna) with gain 2.1, −3.9 and 2.5 dBi, and it is dual polarized. The size of prototype patch antenna is 20 × 20 mm 2 which is reduced about 47% in comparison to conventional patch antenna at 2.5 GHz. The second antenna is designed by the use of interdigital capacitor and spiral inductor. Dimensions of antenna are 15.5×12 mm 2 , so the size is reduced about 69% in comparison to conventional microstrip patch antennas at 1.8 GHz. The second tri-band antenna operates at 1060 MHz, 1800 MHz and 2500 MHz in which two frequencies (1.8 and 2.5 GHz) are suitable for GMS and WLAN applications. Both structures have been designed and fabricated on FR4 low cost substrate with ε r = 4.4 and thickness of 1.6 mm. All simulations are done with CST and HFSS. Equivalent circuit and experimental results are also presented and compared.

2008, Microwave and Optical Technology Letters

A broadband microstrip patch antenna with U-shaped parasitic elements is proposed and analyzed using equivalent circuit theory concept. The effects of gap between the main patch and the U-shaped parasitic elements, substrate thickness, and the feed point location are analyzed to obtain the optimum conditions for broadband operation of the antenna. The antenna shows an operational frequency band from 4.88 to 6.44 GHz with 28.36% bandwidth at center frequency 5.5 GHz. The radiation patterns of the proposed antenna are similar to that of a rectangular patch. The antenna shows 3-dB beam width of 98.6° at lower resonance frequency whereas it is 77.6° at higher resonance frequency. The theoretical results are in good agreement with experimental results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2059–2063, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23573

International Journal of Advanced Research in Computer Engineering & Technology (IJARCET) ijarcet

 Abstract— We are living in the technological era, were we preferred to have the portable devices rather than unmovable devices. We are isolating our self rom the wires and we are becoming the habitual of wireless world what makes the device portable? I guess physical dimensions (mechanical) of that particular device, but along with this the electrical dimension is of the device is also of great importance. Reducing the physical dimension of the antenna would result in the small antenna but not electrically small antenna. We have different definition for the electrically small antenna but the one which is most appropriate is, where k is the wave number and is equal to and a is the radius of the imaginary sphere circumscribing the maximum dimension of the antenna. As the present day electronic devices progress to diminish in size, technocrats have become increasingly concentrated on electrically small antenna (ESA) designs to reduce the size of the antenna in the overall electronics system. Researchers in many fields, including RF and Microwave, biomedical technology and national intelligence, can benefit from electrically small antennas as long as the performance of the designed ESA meets the system requirement. Keywords— electrically small antenna, microstrip patch antenna

International Journal of Latest Technology in Engineering, Management & Applied Science -IJLTEMAS (www.ijltemas.in)

Microstrip patch antenna is a lightweight, inexpensive antenna on which electronics like LNA's and SSPA's can be integrated easily. It is applied to different applications such as Bluetooth, WLAN, satellite communication, biomedical applications, telemedicine and so on due to its Compact size. This work aims at reducing the size of the antenna using meander slot. In this work we explored reduction, which makes it appropriate to apply for more applications. Meander slot follows an asymmetrical path which increases the path for current flow. The simulated results show 71.34% of size reduction for 3.3GHz resonating frequency and 25.04% for 5.5GHz as compared to rectangular patch. This work also analysis the probe and edge feeding techniques and comparative results are tabulated feeding techniques.

Juraj Bartolic

2001, 11th International Conference on Antennas and Propagation (ICAP 2001)

Yasser Ahmed Fadh

The Journal of The University of Duhok

Ijariit Journal

2023, Bulletin of Electrical Engineering and Informatics

This paper designs, simulates, and analyzes the S-band microstrip patch antenna (MPA) for wireless applications. FR-4 (lossy) and Rogger RT/duroid, whose dielectric permittivity is 4.3 and 2.2, respectively, have been used as substrate materials. Simulation is done by computer simulation technology (CST) suite studio 2019 software. Simulations with FR-4 material showed that the return loss was-20.405 dB, the gain was 2.592 dB, the directivity was 7.47 dBi, the voltage standing wave ratio (VSWR) was 1.221, the bandwidth (BW) was 0.0746 GHz, and the efficiency was 34.69%. Also, Rogers RT/duroid material gives results of a return loss of-12.542 dB, a bandwidth (BW) of 0.0349 GHz, a gain of 8.092 dB, a directivity of 8.587 dBi, and an efficiency of 94.24%. The main goal of this antenna is to have a low return loss while getting as close as possible to a VSWR of 1. This will improve the antenna's gain, directivity, and efficiency compared to other antennas. Copper was used to make the patch and the ground, which were 0.35 mm and 0.0077 mm thick, respectively. The results obtained from the proposed antenna were better than those previously published in various in modern scientific journal and conference papers.

sciepub.com SciEP

In this paper, we have achieved an efficient rectangular patch antenna with optimized parameters by using MATLAB. The proposed antenna is a type of radio antenna with a low profile which is mounted on a flat surface. It consists of a flat rectangular sheet or patch of metal, mounted over a larger sheet of metal called a ground plane. A resonant frequency of 3 GHz is achieved with improved parameters like high return loss, Low VSWR, High directivity & gain, High efficiency. So the proposed antenna can be suitable for the radio astronomy & space research applications.

2008, Progress In Electromagnetics Research B

SHEKHAR YADAV

2019, International Journal of RF and Microwave Computer-Aided Engineering

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