*2.4.2 Passive intermodulation*

As is known, in active RF devices there can occur intermodulation products of applied two or more tones at the output of the device. Similar phenomenon can be seen at antennas because of two main reasons: nonlinearity of material and nonlinearity of contact.

To avoid multipaction and passive intermodulation there are some published standards for design and verification phases. One of them is ECSS-E-20-01A Rev.1—*multipaction design and test*.

## **3. Frequency allocations for space missions**

Radio frequency spectrum usage must be regulated to guarantee a costeffective and high-capacity utilization for terrestrial and satellite communication systems all over the world. Although, the frequency intervals used for the spacecrafts vary according to the characteristics of the TM/TC modules and payload on the space vehicle, they are determined and coordinated by International Telecommunication Union (ITU). ITU, which is a United Nations structure, acts under the contract accepted by the executives of member states. For this aim, ITU holds a forum and owing to this forum it can do coordination of radiofrequency spectrum, define standards for communication protocols, device or equipment characteristics and interference levels between private sector and member states [5].

There are radio communication services defined for space applications to transmit or receive radio signals by the Radio Communication Regulations. Those are

**145**

sections.

*Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

• MSS: mobile satellite service

**Figure 3.**

*regulations (2016 edition)).*

• SOS: space operation service

• SRS: space research service

• RSS: radio determination satellite service

as accepted and published in 1988. It is seen in **Figure 3**.

**4. Antenna types used on spacecrafts**

Based on the radio communication services mentioned above, the defined or allocated frequency bands can be private for one of them or shared between these services. Moreover, the world has been divided into three parts for the coordination

*ITU regions of the world for frequency allocation as given in [6] (image courtesy of ITU, source: ITU radio* 

Region 1 consists of Europe, Africa, the Middle East and the land of former USSR; Region 2 is the Americas and finally region 3 is Asia Pacific but not including the Middle East and land of former USSR. In **Table 1**, some specific frequency bands used for space communication are presented. An interested reader to see full frequency spectrum allocations of terrestrial and space application can visit the web

There are many different spacecrafts to conduct various missions for humankind. Consequently, they need different subsystems like communication subsystems, microwave imaging payloads, instrument landing systems which use radar technology, scientific and experimental research devices to explore deep-space and many others. This leads to a need for different type of antennas to fulfill defined missions successfully. Spacecrafts can be divided into four main groups: missile launchers, satellites, radio astronomy and deep space vehicles. Based on this categorization some antenna types used on those vehicles will be reviewed in the following

site created by IEEE Geoscience and Remote Sensing Society given in [7].


#### **Figure 3.**

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

*Multipaction* is, basically, an event that can be reason of breakdown because of high power RF signal in a vacuum or near vacuum medium. It can reduce RF output power of device, cause noise in RF signal and even *corona discharge* because of ionization in presence of electromagnetic wave. Therefore, it can result a catastrophic failure of an antenna, RF component and even another payload module. There are two main factors for multipaction: high RF power and vacuum medium. Thus, related RF components including antennas should be either analyzed or tested for these phenomena. There is an analysis tool designed by ESA/ESTEC named as "ECSS Multipactor Tool". By using this tool one can calculate threshold and safety margin levels for pre-defined structures according to the operating frequency, impedance, RF power level, material finishing and minimum distance between

As is known, in active RF devices there can occur intermodulation products of applied two or more tones at the output of the device. Similar phenomenon can be seen at antennas because of two main reasons: nonlinearity of material and nonlin-

To avoid multipaction and passive intermodulation there are some published standards for design and verification phases. One of them is ECSS-E-20-01A

Radio frequency spectrum usage must be regulated to guarantee a costeffective and high-capacity utilization for terrestrial and satellite communication systems all over the world. Although, the frequency intervals used for the spacecrafts vary according to the characteristics of the TM/TC modules and payload on the space vehicle, they are determined and coordinated by International Telecommunication Union (ITU). ITU, which is a United Nations structure, acts under the contract accepted by the executives of member states. For this aim, ITU holds a forum and owing to this forum it can do coordination of radiofrequency spectrum, define standards for communication protocols, device or equipment characteristics and interference levels between private

There are radio communication services defined for space applications to transmit or receive radio signals by the Radio Communication Regulations. Those are

**2.4 Other effects**

metal tips or edges.

earity of contact.

*2.4.2 Passive intermodulation*

Rev.1—*multipaction design and test*.

sector and member states [5].

• ASS: amateur satellite service

• FSS: fixed satellite service

• ISS: inter-satellite service

• BSS: broadcasting satellite service

• EES: Earth exploration satellite service

**3. Frequency allocations for space missions**

*2.4.1 Multipaction and corona discharge*

**144**

*ITU regions of the world for frequency allocation as given in [6] (image courtesy of ITU, source: ITU radio regulations (2016 edition)).*


Based on the radio communication services mentioned above, the defined or allocated frequency bands can be private for one of them or shared between these services. Moreover, the world has been divided into three parts for the coordination as accepted and published in 1988. It is seen in **Figure 3**.

Region 1 consists of Europe, Africa, the Middle East and the land of former USSR; Region 2 is the Americas and finally region 3 is Asia Pacific but not including the Middle East and land of former USSR. In **Table 1**, some specific frequency bands used for space communication are presented. An interested reader to see full frequency spectrum allocations of terrestrial and space application can visit the web site created by IEEE Geoscience and Remote Sensing Society given in [7].

## **4. Antenna types used on spacecrafts**

There are many different spacecrafts to conduct various missions for humankind. Consequently, they need different subsystems like communication subsystems, microwave imaging payloads, instrument landing systems which use radar technology, scientific and experimental research devices to explore deep-space and many others. This leads to a need for different type of antennas to fulfill defined missions successfully. Spacecrafts can be divided into four main groups: missile launchers, satellites, radio astronomy and deep space vehicles. Based on this categorization some antenna types used on those vehicles will be reviewed in the following sections.


**147**

*Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

2200–2290 Earth exploration

Fixed Mobile 5.391 Space operation (space-to-Earth) (space-to-space) Space research (space-to-Earth) (space-to-space)

5.392

Fixed Fixed satellite (Earth-to-space) Mobile 5.463 5.462A

8025–8400 Earth exploration satellite (space-to-Earth)

satellite (spaceto-Earth) (space-to-space)

**Primary allocation European common** 

**allocation**

Fixed Mobile 5.391

5.392 EU15 EU27

Fixed Fixed satellite (Earth-to-space) Meteorological satellite (Earth-to-space) Mobile 5.463 5.462A EU2 EU27

Earth exploration satellite (space-to-Earth) (space-to-space)

Space operation (space-to-Earth) (space-to-space) Space research (space-to-Earth) (space-to-space)

Earth exploration satellite (space-to-Earth)

**Applications Standard**

Defense systems Fixed PMSE Radio astronomy Space research

Defense systems Earth exploration satellite Fixed Radio astronomy Radio determination applications

**Frequency band (MHz)**

**4.1 Antennas for missile launchers**

**Table 1.**

*4.1.1 Transmission line antennas*

following subsections some examples are given.

*Some specific frequency bands for space communication defined by ITU.*

In order to acquire TM/TC communication, guidance, transmitting and receiving radar signals, sending video and image, communicating with satellite after departing, there are many antennas used on missile launchers. Up to now, a lot of different antenna types have been designed for this purpose. However, since the main objective of missile is military usage (ballistic missiles a good example), it is hard to find adequate info about subsystems on them in open literature. In the

Particularly for TM/TC communication subsystems, missiles need Omnidirectional antennas to communicate with ground stations. Since antennas are the final or first component of RF transmitter or receiver, respectively, they must be on outward or just underneath surface of missiles with RF transparent radome. Nevertheless, they must comply with aerodynamic structure of missile. Otherwise, it will increase air-drag during trip along the atmosphere. Therefore, if antennas will be used over the surface of a missile, they must be compatible with aerodynamic structure. A well-known type of antenna for this goal is *transmission line antenna* [8] which is also commonly used for other aerospace vehicles. It is known that radiation resistance of a transmission line is quite small. In order to increase the radiated power rather than power dissipated as heat, a transmission line can be terminated with reactive elements like capacitors, conducting bridges or open ends. Based on this technique, in [8] four types of them have been presented. These are *inverted L antenna, shunt-driven inverted L antenna with open end, shunt-driven* 

*inverted L antenna with capacitive end loading* and finally *m antenna.*


*Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

#### **Table 1.**

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

**Primary allocation European common** 

**allocation**

Amateur Amateur satellite

Amateur Amateur satellite Radiolocation

(active) 5.279A 5.277 EU2 EU12

Earth exploration satellite

Aeronautical radio navigation 5.328

Radio navigation-satellite (space-to-Earth) (spaceto-space) 5.328B 5.328A

Earth exploration satellite

Radio navigation satellite (space-to-Earth) (spaceto-space) 5.328b 5.329

Space research (active)

Aeronautical radio navigation

Earth exploration satellite (Earth-to-space) (space-to-space)

Space operation (Earth-tospace) (space-to-space) Space research (Earth-tospace) (space-to-space)

Radio navigation satellite (space-to-Earth) (spaceto-space) 5.208B 5.328B

(active) Radiolocation

5.329a

5.329A 5.341 5.362B

Fixed Mobile 5.391

5.392 EU2 EU15 EU27

5.331 EU2 5.332

**Applications Standard**

EN 301 783

EN 301 783

EN 302 645

EN 302 645

EN 302 645

Amateur Amateur satellite

Active sensors (satellite) Amateur Amateur satellite

Aeronautical navigation GALILEO GLONASS GNSS repeater

Active sensors (satellite) Defense systems GLONASS GNSS repeater GPS Radiolocation (civil)

GALILEO GLONASS GNSS pseudolites GNSS repeater GPS

Defense systems Fixed PMSE Space research

**Frequency band (MHz)**

144–146 Amateur

434.79–438 Amateur

Amateur satellite

Radiolocation Earth explorationsatellite (active) 5.279A 5.138 5.271 5.276 5.277 5.280 5.282

Radio navigation satellite (space-to-Earth) (space-tospace) 5.328B 5.328A

satellite (active) Radiolocation Radio navigation satellite (space-to-Earth) (space-tospace) 5.328B 5.329

5.216

1164–1215 Aeronautical radio navigation 5.328

1215–1240 Earth exploration

5.329A Space research (active) 5.330 5.331 5.332

1559–1610 Aeronautical radio navigation Radio navigation satellite (space-to-Earth) (space-tospace) 5.208B 5.328B

> 5.329A 5.341 5.362B 5.362C

satellite (Earthto-space) (space-to-space)

2025–2110 Earth exploration

Fixed Mobile 5.391 Space operation (Earth-to-space) (space-to-space) Space research (Earthto-space) (space-tospace) 5.392 5.392

**146**

*Some specific frequency bands for space communication defined by ITU.*

### **4.1 Antennas for missile launchers**

In order to acquire TM/TC communication, guidance, transmitting and receiving radar signals, sending video and image, communicating with satellite after departing, there are many antennas used on missile launchers. Up to now, a lot of different antenna types have been designed for this purpose. However, since the main objective of missile is military usage (ballistic missiles a good example), it is hard to find adequate info about subsystems on them in open literature. In the following subsections some examples are given.

#### *4.1.1 Transmission line antennas*

Particularly for TM/TC communication subsystems, missiles need Omnidirectional antennas to communicate with ground stations. Since antennas are the final or first component of RF transmitter or receiver, respectively, they must be on outward or just underneath surface of missiles with RF transparent radome. Nevertheless, they must comply with aerodynamic structure of missile. Otherwise, it will increase air-drag during trip along the atmosphere. Therefore, if antennas will be used over the surface of a missile, they must be compatible with aerodynamic structure. A well-known type of antenna for this goal is *transmission line antenna* [8] which is also commonly used for other aerospace vehicles. It is known that radiation resistance of a transmission line is quite small. In order to increase the radiated power rather than power dissipated as heat, a transmission line can be terminated with reactive elements like capacitors, conducting bridges or open ends. Based on this technique, in [8] four types of them have been presented. These are *inverted L antenna, shunt-driven inverted L antenna with open end, shunt-driven inverted L antenna with capacitive end loading* and finally *m antenna.*

**Figure 4.** *Inverted L antenna for using on missiles [8].*

Inverted L antenna is a simple wire antenna structure, which is folded on a point of a transmission line as illustrated in **Figure 4**. It should be emphasized that its open end is at the reverse direction to flight in order to afford aerodynamic conformity to the missile. It is fed by coaxial line. Distance between the ground surface of missile and the antenna wire is b/2, horizontal length of the antenna is s2 and the diameter of wire that is used to form the antenna is 2a. Inverted L antenna has been analyzed based on the transmission line theory in [8]. Therefore, the diameter of wire 2a and height over surface b/2 must be smaller than operating wavelength. The derived relations for transmission line modeling of these antennas are valid for 2a < 0.01λ and b ≤ 0.1λ as mentioned in [8].

Equivalent circuit model of inverted L antenna is shown in **Figure 5**.

Using transmission line theory radiation resistance of the antenna can be derived as

$$\mathcal{R}^{\epsilon} = \frac{\mathfrak{z}\mathfrak{o}\beta^{2}b^{2}}{\sin^{2}\beta\mathfrak{s}\_{z}} \left| \mathfrak{z} - \frac{\sin 2\beta\mathfrak{s}\_{z}}{\mathfrak{z}\beta\mathfrak{s}\_{z}} \right\rangle \tag{1}$$

**149**

**Figure 8.**

*Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

*Equivalent circuit model of inverted L antenna: end-driven open-end section of line [8].*

*Shunt-driven inverted L antenna with open end for using on missiles [8].*

*Equivalent circuit model of shunt-driven inverted L antenna with open end: shunt-driven line with an open* 

*Shunt-driven inverted L antenna with capacitive end loading for using on missiles [8].*

**Figure 5.**

**Figure 6.**

**Figure 7.**

*and a short-circuited termination [8].*

where β is phase constant for the transmission line [8].

The second type of transmission line antenna is shunt-driven inverted L antenna with open end as illustrated in **Figure 6**. In this case, there is a shorting line with a distance of s1 from center of the feeding line. Again open end is opposite to the direction of flight.

Its equivalent circuit model is presented in **Figure 7**.

By using transmission line theory radiation resistance of the antenna can be derived as given in [8].

$$\mathbf{R}^{\mathfrak{e}} = \frac{\mathbf{\hat{z}} \otimes \boldsymbol{\beta}^{\mathfrak{e}} \mathbf{\hat{b}}^{\mathfrak{z}}}{\cos^{\mathfrak{e}} \boldsymbol{\beta} \mathbf{\hat{s}}\_{\mathfrak{z}}} \left\{ \frac{\mathbf{1}}{2} \left[ \cos^{\mathfrak{e}} \boldsymbol{\beta} \mathbf{s} + \sin^{\mathfrak{e}} \boldsymbol{\beta} \mathbf{s}\_{\mathfrak{z}} + \cos^{\mathfrak{e}} \boldsymbol{\beta} \mathbf{s}\_{\mathfrak{z}} \right] - \cos \boldsymbol{\beta} \mathbf{s} \cos \boldsymbol{\beta} \mathbf{s}\_{\mathfrak{z}} \frac{\sin \boldsymbol{\beta} \mathbf{s}\_{\mathfrak{z}}}{\mathbf{b} \mathbf{s}\_{\mathfrak{z}}} \right\}, \tag{2}$$
  $\text{where } \cos \boldsymbol{\beta} \mathbf{s} \neq \mathbf{0}$ 

Here, s = s1 + s2. If this antenna is modified by adding a tunable capacitor instead of open end it will be easy to tune input impedance of the antenna. It is shunt-driven inverted L antenna with capacitive end loading. Its illustration is shown in **Figure 8**.

*Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

#### **Figure 5.**

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

Inverted L antenna is a simple wire antenna structure, which is folded on a point of a transmission line as illustrated in **Figure 4**. It should be emphasized that its open end is at the reverse direction to flight in order to afford aerodynamic conformity to the missile. It is fed by coaxial line. Distance between the ground surface of missile and the antenna wire is b/2, horizontal length of the antenna is s2 and the diameter of wire that is used to form the antenna is 2a. Inverted L antenna has been analyzed based on the transmission line theory in [8]. Therefore, the diameter of wire 2a and height over surface b/2 must be smaller than operating wavelength. The derived relations for transmission line modeling of these antennas are valid for

Equivalent circuit model of inverted L antenna is shown in **Figure 5**. Using transmission line theory radiation resistance of the antenna can be

2 2

b

30 sin2 1 sin 2 *<sup>e</sup> <sup>b</sup> <sup>s</sup> <sup>R</sup>*

ì ü = - í ý

The second type of transmission line antenna is shunt-driven inverted L antenna with open end as illustrated in **Figure 6**. In this case, there is a shorting line with a distance of s1 from center of the feeding line. Again open end is opposite to the

By using transmission line theory radiation resistance of the antenna can be

ì ü <sup>=</sup> í ý é ù ++ - ë û î þ

Here, s = s1 + s2. If this antenna is modified by adding a tunable capacitor instead of open end it will be easy to tune input impedance of the antenna. It is shunt-driven inverted L antenna with capacitive end loading. Its illustration is shown in **Figure 8**.

e 22 2 1 2 12 2

30 b 1 sin s <sup>R</sup> cos sin s cos s cos s cos s , cos s 2 bs

 b 2 2

 b

î þ

 b

2 1

 bb

*s* (2)

*s s*

2

where β is phase constant for the transmission line [8].

Its equivalent circuit model is presented in **Figure 7**.

b

b

2

(1)

b

b

2a < 0.01λ and b ≤ 0.1λ as mentioned in [8].

*Inverted L antenna for using on missiles [8].*

**148**

derived as

**Figure 4.**

direction of flight.

derived as given in [8].

b

b

2 2

b

where cos s 0

¹

*Equivalent circuit model of inverted L antenna: end-driven open-end section of line [8].*

#### **Figure 6.**

*Shunt-driven inverted L antenna with open end for using on missiles [8].*

#### **Figure 7.**

*Equivalent circuit model of shunt-driven inverted L antenna with open end: shunt-driven line with an open and a short-circuited termination [8].*

**Figure 8.** *Shunt-driven inverted L antenna with capacitive end loading for using on missiles [8].*

**Figure 9.**

*m-Antenna with capacitive end loading for using on missiles [8].*

#### **Figure 10.**

*Equivalent circuit model of m antenna: shunt-driven line with short-circuited terminations [8].*

In order to derive the radiation resistance of reactive element ended inverted L antenna the relations given in [9] can be used. For the sake of brevity, derivation of radiation resistance has not been given within text.

The final type of transmission line antenna is m-antenna. Its illustration is given in **Figure 9**.

Its equivalent circuit model is presented in **Figure 10**.

Similarly, as used in previous antenna types, using transmission line theory radiation resistance of the antenna can be derived as [8].

$$\begin{aligned} R' &= \frac{\Im \otimes \beta^2 b^2}{\sin^2 \beta \boldsymbol{\varepsilon}\_z} \Bigg\{ \frac{1}{2} \Big[ \sin^2 \beta \boldsymbol{s} + \sin^2 \beta \boldsymbol{\varepsilon}\_z + \sin^2 \beta \boldsymbol{\varepsilon}\_z \Big] - \left( \frac{\boldsymbol{s}\_z^2 + \boldsymbol{s}\_z \boldsymbol{s}\_z + \boldsymbol{s}\_z^2}{\beta \boldsymbol{s}\_z \boldsymbol{s}\_z} \right) \sin \beta \boldsymbol{s} \sin \beta \boldsymbol{\varepsilon}\_z \sin \beta \boldsymbol{\varepsilon}\_z \Big] \\ & \left( \sin \beta \boldsymbol{s} \neq \mathbf{0} \right) \end{aligned} \tag{3}$$

and s = s1 + s2.

Up to date, many different versions of those basic antennas have been published in the literature. Particularly, their printed circuit versions are also available and used for different communication devices in cellular phones, tablets and portable computers as well.

#### *4.1.2 Extremely thin and omnidirectional slot antenna array for launch vehicles*

Another basic antenna used on missiles is conformal slot array structure. In order to get enhanced coverage for launch vehicles, array antennas are versatile

**151**

**Figure 11.**

**Figure 12.**

and effective. Almost omnidirectional pattern can be achieved using circumferential or conformal array antennas on the launch vehicles. There are various examples for this type in the general literature. One of them is presented in [10] Its outline illustration is shown in **Figure 11**. As shown in this figure eight slot elements were used and to decrease the number of branch lines the author used series feedline as shown in **Figure 12**. Input impedance of each slot antenna element is designed as 50 Ω. Moreover, in **Figure 12** matching of the main input port of the array is explained in detail. For matching 6 Ω input impedance of eightelement slot array to 50 Ω, λ/4 transformer is employed at the input. To suppress higher order modes and edge excitation of the slots, bolts are inserted circumferentially to form a rectangular transmission line. In Ref. [10], it is particularly

*Series stripline feed structure for the array of eight slots [10].*

*Outline drawing of stripline-fed cavity-backed slot array antenna on space launch vehicle [10].*

*Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116* *Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

**Figure 11.**

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

In order to derive the radiation resistance of reactive element ended inverted L antenna the relations given in [9] can be used. For the sake of brevity, derivation of

*Equivalent circuit model of m antenna: shunt-driven line with short-circuited terminations [8].*

The final type of transmission line antenna is m-antenna. Its illustration is given

Similarly, as used in previous antenna types, using transmission line theory

 b

22 2 1 12 2 2 1 2 1 2

*<sup>e</sup> <sup>b</sup> s ss s <sup>R</sup> ss s sin s sin s sin s*

*4.1.2 Extremely thin and omnidirectional slot antenna array for launch vehicles*

2 2 2 2

2 1 2

*s s s*

= ++ - í ý é ù

Up to date, many different versions of those basic antennas have been published in the literature. Particularly, their printed circuit versions are also available and used for different communication devices in cellular phones, tablets and portable

Another basic antenna used on missiles is conformal slot array structure. In order to get enhanced coverage for launch vehicles, array antennas are versatile

 b

ì ü ï ï æ ö + +

ë û ç ÷ ï ï î þ è ø

bbb

(3)

radiation resistance has not been given within text.

*m-Antenna with capacitive end loading for using on missiles [8].*

Its equivalent circuit model is presented in **Figure 10**.

radiation resistance of the antenna can be derived as [8].

bb

30 1 sin sin sin

**150**

in **Figure 9**.

**Figure 10.**

**Figure 9.**

( )

and s = s1 + s2.

computers as well.

b

*sin s*

b

sin 2 0

¹

b *Outline drawing of stripline-fed cavity-backed slot array antenna on space launch vehicle [10].*

**Figure 12.** *Series stripline feed structure for the array of eight slots [10].*

and effective. Almost omnidirectional pattern can be achieved using circumferential or conformal array antennas on the launch vehicles. There are various examples for this type in the general literature. One of them is presented in [10] Its outline illustration is shown in **Figure 11**. As shown in this figure eight slot elements were used and to decrease the number of branch lines the author used series feedline as shown in **Figure 12**. Input impedance of each slot antenna element is designed as 50 Ω. Moreover, in **Figure 12** matching of the main input port of the array is explained in detail. For matching 6 Ω input impedance of eightelement slot array to 50 Ω, λ/4 transformer is employed at the input. To suppress higher order modes and edge excitation of the slots, bolts are inserted circumferentially to form a rectangular transmission line. In Ref. [10], it is particularly

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*


#### **Table 2.**

*Physical design parameters of conformal stripline fed slot array antenna [10].*

highlighted that spacing between each bolt and number of bolts are crucial to obtain continuous short circuit around slot aperture and also at transition area from RF connector to stripline feed.

Design parameters of this conformal array are presented in **Table 2**. Those physical design parameters were obtained for a substrate having a dielectric permittivity of 2.1 and a dielectric cover whose permittivity is 2.54. The dielectric cover was used to protect the array antenna from heat arising because of atmospheric friction. To obtain 50 Ω input impedance for each slot antenna, offset feeding technique was used.

Azimuth and elevation patterns of the array are presented in **Figures 13** and **14**, respectively. In these figures, omnidirectional radiation pattern characteristic is seen clearly around the launch vehicle.

In those figures red line represents the radiation pattern with superstrate and black dashed line represents radiation pattern without superstrate.

Today, different types of wrap around slot arrays are still being used on launch vehicles to form omnidirectional radiation pattern around the vehicle. The number of the array element can be increased depending on the circumferential electrical

**153**

*Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

structure of the vehicle.

**Figure 14.**

**4.2 Satellite antennas**

array antenna systems.

length. Thanks to those antennas, TM/TC RF signals can be sent or received easily. An interested reader can find commercial products based on this type, since it has many advantages like ease of manufacturing and good conformity to aerodynamic

*Radiation pattern of the slot array in the elevation plane with and without dielectric cover [10].*

Up to date, numerous antennas have been designed and employed for different space missions. As mentioned in previous parts, most of them are for satellite communication systems like TM/TC and PDT subsystems, broadcast payload etc. As given in the first section, satellites are usually categorized according to their orbits. Those orbits define and affect general characteristics of satellites to be designed and manufactured for power generation from their solar panels, communication period and slot with ground station, radiation endurance, parts to be used because

of atmospheric effects like atomic oxygen and their payload specifications. After frequency definition for subsystems, types of antennas to be used for communication, remote sensing instrument and scientific instruments are selected. For example, circularly polarized antennas are usually preferred for TM/TC antennas not to be affected from polarization mismatch, which can be caused by maneuvers during low earth orbiting phases and atmospheric effects like Faraday rotation [11]. Besides antennas used on small satellites should be as low profile as possible due to surface and volume restrictions. However, for PDT and remote sensing applications medium and high gain antennas are needed. To use high gain and therefore narrow beamwidth antennas efficiently, they should be steered whether directing whole satellite platform or using additional steering mechanism like electromechanical structures or electronically steerable phased

As is well known there are different types of antennas used for satellites but since there is very limited place in this part, only some noteworthy ones will be

taken into consideration and presented for the sake of brevity.

**Figure 13.** *Radiation pattern of the slot array in the azimuth plane with and without dielectric cover [10].*

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

**Description Dimensions (mm)**

Slot size without coating 64.77 × 2.54 Minimum cavity size 50.8 × 83.82 × 2.39 Feeding point position from end of slot to obtain 50 Ω 15.24 L (slot length) where tεr = 0.15 57.4 L (slot length) where tεr = 0.10 58.17

highlighted that spacing between each bolt and number of bolts are crucial to obtain continuous short circuit around slot aperture and also at transition area

*Physical design parameters of conformal stripline fed slot array antenna [10].*

L (slot length) where tεr = 0.10 55.88 Cavity size 50.8 × 83.82 × 2.310 Feeding point position from end of slot to obtain 50 Ωs 15.24

Design parameters of this conformal array are presented in **Table 2**. Those physical design parameters were obtained for a substrate having a dielectric permittivity of 2.1 and a dielectric cover whose permittivity is 2.54. The dielectric cover was used to protect the array antenna from heat arising because of atmospheric friction. To obtain 50 Ω input impedance for each slot antenna, offset feeding technique was used.

Azimuth and elevation patterns of the array are presented in **Figures 13** and **14**, respectively. In these figures, omnidirectional radiation pattern characteristic is

In those figures red line represents the radiation pattern with superstrate and

Today, different types of wrap around slot arrays are still being used on launch vehicles to form omnidirectional radiation pattern around the vehicle. The number of the array element can be increased depending on the circumferential electrical

black dashed line represents radiation pattern without superstrate.

*Radiation pattern of the slot array in the azimuth plane with and without dielectric cover [10].*

from RF connector to stripline feed.

**Single slot antenna**

**Array of slots**

**Table 2.**

seen clearly around the launch vehicle.

**152**

**Figure 13.**

**Figure 14.** *Radiation pattern of the slot array in the elevation plane with and without dielectric cover [10].*

length. Thanks to those antennas, TM/TC RF signals can be sent or received easily. An interested reader can find commercial products based on this type, since it has many advantages like ease of manufacturing and good conformity to aerodynamic structure of the vehicle.

#### **4.2 Satellite antennas**

Up to date, numerous antennas have been designed and employed for different space missions. As mentioned in previous parts, most of them are for satellite communication systems like TM/TC and PDT subsystems, broadcast payload etc. As given in the first section, satellites are usually categorized according to their orbits. Those orbits define and affect general characteristics of satellites to be designed and manufactured for power generation from their solar panels, communication period and slot with ground station, radiation endurance, parts to be used because of atmospheric effects like atomic oxygen and their payload specifications.

After frequency definition for subsystems, types of antennas to be used for communication, remote sensing instrument and scientific instruments are selected. For example, circularly polarized antennas are usually preferred for TM/TC antennas not to be affected from polarization mismatch, which can be caused by maneuvers during low earth orbiting phases and atmospheric effects like Faraday rotation [11]. Besides antennas used on small satellites should be as low profile as possible due to surface and volume restrictions. However, for PDT and remote sensing applications medium and high gain antennas are needed. To use high gain and therefore narrow beamwidth antennas efficiently, they should be steered whether directing whole satellite platform or using additional steering mechanism like electromechanical structures or electronically steerable phased array antenna systems.

As is well known there are different types of antennas used for satellites but since there is very limited place in this part, only some noteworthy ones will be taken into consideration and presented for the sake of brevity.

#### **Figure 15.**

*Manufactured prototype of cavity-backed antenna with tapered crossed-slot aperture and its 3D radiation pattern [13].*

**Figure 16.**

*Measured S11, co-pol and cross-pol gain results versus frequency for cavity-backed antenna with tapered-slot aperture [13].*

#### *4.2.1 Small antennas for tiny satellites*

There is tremendous demand to accomplish space research at reasonable prices for universities and commercial entities therefore CubeSat is a practical and functional platform for this objective. Dimensions of a 1 U CubeSat are 100 mm x 100 m and it has aluminum T6061 structure with a total mass of up to 1 kg. However, 1 U can be easily enlarged to larger sizes like 2 U, 3 U, etc. Comparing to other satellite platforms, CubeSats have limited volume therefore submodules and antennas should fit into those tiny platforms.

There are good small antenna study examples developed under GAMALINK1 [12] project for CubeSat antennas and one of them is given in [13]. In this study a miniaturized cavity-backed tapered cross-slot antenna has been presented. 38 × 38 mm<sup>2</sup> and 30 × 30 mm<sup>2</sup> footprints have been obtained on substrates having dielectric permittivity 6 and 9.2, respectively, at operating frequency about 2.44 GHz. Manufactured prototype of the antenna and its simulated 3D radiation pattern are shown in **Figure 15**.

Its maximum gain is at boresight and efficiency is small as expected because of miniaturization. However, its tiny dimensions make this antenna beneficial to save space on surfaces of small spacecrafts like CubeSats. In addition, prototype was manufactured to verify the simulation results shown in **Figure 16** as mentioned

**155**

**Figure 18.**

*Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

can be gathered to form an array.

*4.2.2 Deployable large antennas for tiny satellites*

[14–22].

**Figure 17.**

*JPL-Caltech).*

in [13]. S11, gain and cross pol gain are presented in this figure and the measured values support electromagnetic simulation results. These types of miniaturized antennas have low efficiency. Nonetheless, since they have small footprints they can be installed to the CubeSats easily especially for TM/TC communication and even for Inter Satellite Link (ISL). Therefore, for distinctive missions even 3 or 4 of them

However, an interested reader should review other studies where mesh and optically transparent or mesh type antennas are proposed as well as small antennas

For some specific operations electrically large antennas can be needed on CubeSats. Those antennas are folded, stowed or packed in a CubeSat before and during launch process. After satellite platform is placed into orbit they are deployed to conduct their missions. For this aim, there are deployable antenna examples

A stowed 0.5 m Ka-band mesh reflector antenna was installed into RaInCube platform to initiate usage of Ka-Band radar for meteorology on a low-cost and fast

*Ka-band deployable parabolic dish antenna which has 30 ribs similar to an umbrella to be stowed and installed into RaInCube platform. Left deployed and right stowed into RaInCube (image courtesy of NASA/*

*Measured and calculated radiation pattern of the deployable mesh reflector antenna model. (a)* ϕ *= 0°. (b)* 

ϕ *= 90°. (Reprinted, with permission, from [25], © 2016 IEEE).*

where cutting edge mechanical technologies are employed (**Figure 17**).

<sup>1</sup> GAMALINK (Generic SDR-bAsed Multifunctional spAce LINK) is a project for European Union's FP7-Seventh Framework Programme for research, technological development and demonstration under grant agreement no 312830.

#### *Antennas for Space Applications: A Review DOI: http://dx.doi.org/10.5772/intechopen.93116*

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

*Manufactured prototype of cavity-backed antenna with tapered crossed-slot aperture and its 3D radiation* 

There is tremendous demand to accomplish space research at reasonable prices for universities and commercial entities therefore CubeSat is a practical and functional platform for this objective. Dimensions of a 1 U CubeSat are 100 mm x 100 m and it has aluminum T6061 structure with a total mass of up to 1 kg. However, 1 U can be easily enlarged to larger sizes like 2 U, 3 U, etc. Comparing to other satellite platforms, CubeSats have limited volume therefore submodules and antennas

*Measured S11, co-pol and cross-pol gain results versus frequency for cavity-backed antenna with tapered-slot* 

There are good small antenna study examples developed under GAMALINK1 [12] project for CubeSat antennas and one of them is given in [13]. In this study a miniaturized cavity-backed tapered cross-slot antenna has been presented.

ing dielectric permittivity 6 and 9.2, respectively, at operating frequency about 2.44 GHz. Manufactured prototype of the antenna and its simulated 3D radiation

<sup>1</sup> GAMALINK (Generic SDR-bAsed Multifunctional spAce LINK) is a project for European Union's FP7-Seventh Framework Programme for research, technological development and demonstration under

Its maximum gain is at boresight and efficiency is small as expected because of miniaturization. However, its tiny dimensions make this antenna beneficial to save space on surfaces of small spacecrafts like CubeSats. In addition, prototype was manufactured to verify the simulation results shown in **Figure 16** as mentioned

footprints have been obtained on substrates hav-

**154**

38 × 38 mm<sup>2</sup>

**Figure 15.**

*pattern [13].*

**Figure 16.**

*aperture [13].*

*4.2.1 Small antennas for tiny satellites*

should fit into those tiny platforms.

pattern are shown in **Figure 15**.

grant agreement no 312830.

and 30 × 30 mm<sup>2</sup>

in [13]. S11, gain and cross pol gain are presented in this figure and the measured values support electromagnetic simulation results. These types of miniaturized antennas have low efficiency. Nonetheless, since they have small footprints they can be installed to the CubeSats easily especially for TM/TC communication and even for Inter Satellite Link (ISL). Therefore, for distinctive missions even 3 or 4 of them can be gathered to form an array.

However, an interested reader should review other studies where mesh and optically transparent or mesh type antennas are proposed as well as small antennas [14–22].
