Military Radar Applications Research Articles

All-Metal Coding Metasurfaces for Broadband Terahertz RCS Reduction and Infrared Invisibility

With the rapid advancement of modern technology and radar detection systems, electromagnetic (EM) stealth technology has become increasingly significant, particularly in aircraft stealth and military radar applications. In this work, an all-metal metasurface is designed for broadband terahertz radar cross-section (RCS) reduction and infrared invisibility. The all-metal metasurface possesses extremely low infrared emissivity and high polarization conversion in the terahertz band. Through the joint simulation of MATLAB and CST, a genetic algorithm is used to optimize the random phase distribution of 2, 3, and 4-bit metasurfaces, so that the reflected wave is scattered to achieve broadband terahertz RCS reduction. Simulation results show that the metasurface can simultaneously achieve broadband terahertz RCS reduction in 3–5 THz and infrared invisibility in 24–38 THz (8–12.5 μm). The RCS reduction of the coding metasurface is greater than 10 dB compared to the metal plate, and the maximum RCS reduction of the 4-bit metasurface can reach 21.1 dB. Compared to the traditional design method, the proposed method can reduce time consumption and find the optimal result to achieve high performance. We believe the proposed method can provide significant guidance for surface coating in camouflage applications and opens up new possibilities for improving the information capacity of coding metasurfaces.

Terahertz Wave Conversion From Linear to Circular Polarization by Graphene Metasurface Featuring Ultrawideband Tunability

This paper reports a detailed study of a graphene-based metasurface to function as tunable broadband linear to circular polarization converter in the terahertz gap. This device provides a wide polarization conversion band of 2.25 THz (3.75 THz to 6 THz) with an enhanced fractional 3-dB axial ratio bandwidth (FARBW) of 46.15%. The proposed structure consists of a simple tri-layer configuration where the meta-atom comprises a patterned graphene layer on a gold-backed silicon dioxide substrate. The proposed reflective-type linear to circular polarization converter (RLCPC) exhibits both right-handed and left-handed circular orientations of the reflected wave in two halves of the operating spectrum, further validated in terms of polarization ellipses developed by an inhouse code. The lack of experimental setup at the above said frequencies available to the authors in their country has been paid off by verifying the response using a detailed circuit model. The RLCPC maintains a thickness of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_o</i> /7.69 with a lattice size of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_o</i> /8.33. The structure also promises a stable wideband circular polarization conversion up to 20° and a dual-band circular polarization conversion up to 40° incident angle of the electromagnetic wave. This device can be useful for THz beam scanning antennas, RCS reduction and THz antennas for space and military radar applications.

Design and Fabrication of an X-Band Low Noise Amplifier Using FR-4 for Military Radar and Ground Station Receiver Applications

The low noise amplifier (LNA) plays an important role in the radiofrequency receiver front-ends, its main function is to amplify the weak receiving signal from the ground noise, as well as improving the receiver sensitivity. For LNAs which operate in the frequencies higher than the S-band, the printed circuit board (PCB) with high cost substrate materials have been used in almost designs so far, thus increasing the total price of the entire receiving unit. This paper introduces a new approach, in which a LNA has been designed using the FR-4 material, a common, low-cost substrate in PCB fabrication. The proposed LNA will maintain the quality of all of the important parameters such as gain, noise figure in compared with the LNAs designed by high cost material substrates. The stepped impedance matching technique is used in order to reach a balance between the circuit dimension and its efficiency. The frequency range of the proposed LNA lies within the X-band, which is a suitable range for military RADAR applications. Furthermore, it is possible to apply the desired LNA in the ground station receiver front-ends of a Low Earth Orbit (LEO) Earth Observation Satellite system

New compact six-band metamaterial absorber based on Closed Circular Ring Resonator (CCRR) for Radar applications

In this paper, we developed a new design of multiband perfect metamaterials absorber (MTMA) to be operated in the frequency range of 8–12 GHz. Proposed structure consists of a combination of three basic structures which is based on Closed Circular Ring Resonators (CCRR). A dielectric substrate is chosen as FR-4 material of 1.6 mm thickness and 22×22 mm size was used. The proposed (MTMA) operated at six different resonance frequencies 8.3 GHz, 9.2 GHz, 9.88 GHz, 10.66 GHz, 11.16 GHz, and 11.85 GHz with the absorption of 100 %, 100%, 98%, 91%, 98%, and 98% respectively. Negative parameters such as permittivity ɛ permeability (μ) reflective index (n), and impedance (z) were extracted and presented. Results indicated that the MTM absorber was found to extremely independent on the angles of polarization of the incident waves and the absorber was almost insensitive to the incident angle (0° – 90°) for transverse electric (TE) or transverse magnetic (TM) modes. The working principle of the structure is analyzed and illustrated through input impedance, surface current, and the electric field of the structure. The designed absorber was fabricated and experimentally measured in microwave laboratory that shows a good agreement with simulation results. According to the obtained results, the proposed metamaterials absorber is a good candidate for the military RADAR applications.

A Metasurface-Based, Ultrathin, Dual-Band, Linear-to-Circular, Reflective Polarization Converter: Easing uplinking and downlinking for wireless communication

In this article, an ultrathin (+m/15), dual-band, reflective-type linear-tocircular (LTC) electromagnetic (EM) wave-polarization converter is reported. The LTC-polarization conversion has been achieved at two distinct frequency bands viz., 8.34 to 8.71 GHz and 10.3 to 14.73 GHz. In the first band, the structure behaves as a right-hand circular polarization (RHCP) converter, whereas, in the second band, it works as a left-hand circular polarization (LHCP) converter. In both of the frequency bands, the structure exhibits a high-energy conversion efficiency (ECE) of more than 80%. The structure exhibits a 3-dB fractional bandwidth of 39.4% with respect to the center frequency at the higher band while maintaining an axial ratio (AR) of lower than 3 dB in both the frequency bands. To validate the simulated results, the experimental characterization of the proposed metasurface (MS) design has also been carried out in this article. The experimentally measured 3-dB AR bandwidth has been found to be in good agreement with the simulated one. The structure provides angular steering stability up to a 30° incident angle, resulting in its application with beam scanning antennas. The proposed device integrated with antennas may find potential applications in easing the switching of polarization states between uplinking and downlinking for wireless communication in space research as well as in military radar applications.

Design and Characterization of T/R Module for Commercial Beamforming Applications

In the smart antenna system, the transmit and receive (T/R) module is one of the core components as it accounts for nearly 45% of the overall smart antenna system cost. Due to the high implementation cost of the T/R module, the literature was mainly centered around the military and satellite radar applications. However, over the years, the cost of the T/R module has been reduced drastically by leveraging on the advanced manufacturing technology, volume production pricing and adaptation of the commercially available off-the-shelf components, as a result, the adoption of the T/R module in commercial and industrial application become possible. In this work, we have proposed a commercially affordable T/R module that operates in 4.9-5.9 GHz band for commercial and industrial applications. The T/R module was designed, calibrated, and characterized for use in the beamforming smart antenna system. The design process including the circuit, schematic and printed circuit board (PCB) were highlighted. The proposed recursive calibration process managed to correct the phase error to ±1° and amplitude error to ±0.2 dB. In addition, the amplitude distribution of 0.5-1-1-0.5 combination has successfully suppressed the side-lobe level (SLL) to -28.7 dB for 0°, -22.71 dB for ±20° and -12.77 dB for ±40° beam steering. This work is aimed to promote the adoption of the T/R module into the commercial and industrial applications such as public or government infrastructure.

A Compound Reconfigurable Solid State Planar Plasma Antenna

In today’s modern wireless era, reconfigurable antennas play a vital role for functioning under selective frequency bands, different polarizations and radiation patterns according to the users’ application. This article, gives an insight on solid state plasma planar compound reconfigurable antenna for military radar applications at X-band by using array of Lateral PIN (LPIN) diodes. Silicon-dioxide (SiO2) is used as substrate and proximity coupled feeding technique is chosen to avoid biasing problem in LPIN diodes and also to have compatibility with processing on a standard silicon process. The proposed antenna comprises of a square metallic patch placed above the substrate with linear array of LPIN diodes at adjacent sides of patch to provide fine and coarse tuning in frequency over the range of 8-12 GHz and LPIN diodes placed in the ground plane to provide pattern reconfiguration. Hence, the antenna with compound reconfigurability converges to a solution, where a single antenna satisfies the needs for multiple applications.

Carbon-Doped GaN on SiC Materials for Low-Memory-Effect Devices

I. INTRODUCTION Gallium nitride (GaN) high electron mobility transistors (HEMT) are today used in military radar and telecom applications. However, there are still several issues that remain to be solved primarily on the material side. The best performing HEMT devices today are those produced on GaN on silicon carbide (SiC). SiC is used on account of its high thermal conductivity and relatively close lattice match with AlN and GaN. Thermal management of the devices is an issue that needs to be improved and, especially for telecom applications, the memory effect must be reduced in order to simplify linearization of the systems. We present epitaxial GaN on SiC of extraordinary high quality where the thermal barrier to the SiC substrate is minimized and where devices made on this material exhibit a substantially lower memory effect than commercially available devices today. II. RESULTS The epitaxial growth of GaN on SiC substrates starts with the deposition of an aluminium nitride (AlN) wetting layer in order to ensure that the GaN grows in a two-dimensional fashion. The structural quality of the AlN is often rather poor and gives rise to a thermal barrier resistance (TBR) that accumulates heat in the device. This results in a decrease in the device efficiency but may result in a catastrophic thermal breakdown of the device in the worst case. We have optimized the in-situ pre-treatment of the substrate surface and also the initial growth procedure of the AlN so that the AlN layer is grown in a layer-by-layer mode, resulting in a very high structural quality of the AlN and also the subsequent GaN that is grown on top of the AlN. The typical values of the full width of half maximum of XRD rocking curves for the C-doped GaN buffer and the AlN (102) planes are around 200 and 100 arcsec, respectively. The absence of pores in the AlN layer also allows this layer to be made very thin which further reduces the TBR of the structure. Figure 1 shows atomic force microscopy images of a non-optimized (left) and an optimized (right) growth of the 35 nm-thick AlN nucleation layers. The entire growth has been successfully scaled up to 100 mm semi-insulating SiC substrates. The non-uniformity over a 100 mm epiwafer of the total thickness and the sheet resistance are typically less than 1% and 2%, respectively. High electron mobility of ~2100 and ~2300 cm2/V-s was achieved from the 2 nm-thick GaN cap/14 nm-thick Al0.29Ga0.71N/GaN structures with and without a 1 nm-thick AlN exclusion layer, respectively, which is as a result of the low dislocation density and sharp channel interface. On the device level, the distortion of amplitude modulated (AM) signals due to memory effects induced by deep electron traps with long time constants, imposes the practice of linearization schemes using digital pre-distortion which are impractical if the time constants are long, requiring large computational capacity and memory. Reducing the amplitude and time constant of the memory effects will greatly improve the AM performance and reduce the cost to produce the systems. The origin of the trapping is not fully understood however it can be reduced by exchanging the dopant in the buffer layer from Fe, which is the standard dopant, to C. In figure 2, the memory effect is illustrated in a commercial HEMT device with Fe doping and a device produced using C doping in the buffer. The measurement is done by applying a 1 µs long voltage pulse between the drain and source from a quiescent working point. Unfortunately the change of dopant also carries the price of a reduced output power from the device. This issue is currently addressed and a solution is close. III CONCLUSIONS We present material enabling high-power and high-frequency GaN devices to be made, which have substantially better performance and suits the use of GaN HEMT devices in mobile base stations. We highlight here in particular the low TBR, the high mobility, and the 50 times lower memory effect. Figure 1

Miniaturization of Microwave Bandpass Filter for Wideband Applications

This paper presents the miniaturize structure of the wideband bandpass filter using quarter-wavelength short circuited stub structure of the 7th order. The filter design was validated using Roger Duroid RO4350 with a dielectric constant of 3.48, tan δ of 0.019 and thickness of 0.508 mm. The conventional bandpass filter is then reorganized using curve bending to miniaturize the overall size while maintaining the performance of the bandpass response. The proposed structure with 65.3% (3.03 to 5.97 GHz) fractional bandwidth is designed, fabricated, and measured. Both simulations and measured results are found to be in good agreement. The measured passband reflection and transmission coefficient is better than 16 dB and 0.5 dB respectively. This type of wideband bandpass filter is very useful to many microwave wideband communication applications, mostly in civilian and military radar applications.

A Wideband Widebeam Tapered Slot Array Antenna for Active Electronically Scanned Array Antenna

Phased arrays when mounted on aircraft and missiles will be capable of allowing only the desired signals to be received and simultaneously suppress all other unwanted ones incident from hostile sources. This in turn will make them invisible for the radars at the enemy base or on their aircraft. This paper discusses about the design of Phased array antenna for military airborne radar applications. A milllimeter wave active phased array antenna has been developed that is capable of wide scanning angle in both Eand H-planes. In order to achieve wide angle scanning over X-band frequency, a linear tapered slot antenna (LTSA) element has been designed and the resulting element is capable of scanning out to 60 o from broadside in all scan planes for a bandwidth of 11-14GHz and an active reflection coefficient less than -10 dB. Beam scanning angles of above ±45 degrees in the E-plane and ±60 degrees in the H-plane were obtained for an isolated element. An end fire array pattern with half power beamwidth of 14 degrees in E-plane is achieved over 11-14GHz frequency. This design was implemented on linear array antenna consisting of 7-elements and planar array antenna consisting of 49 (7x7) elements. The predicted performance of the antenna was verified by simulation of element patterns, array radiation patterns and S-parameter plot using commercially available electromagnetic simulator HFSS. Since the radar antenna is intended for applications where stealth is important. The antenna aperture consists many radiating elements used for beam-forming and hence through the adjustment of elemental phases steer the beam efficiently. Moreover, they are capable of rejecting all the unwanted components of the received signals while maintaining at the same time sufficient pattern gain in the desired directions. These characteristics can be implemented for stealth applications.

94-GHz TWT for military radar applications

For future military radar applications, high frequency, light-weight TWTs become more and more important. To cover this market, Thomson Tubes Electroniques GmbH several years ago started the development of a 94-GHz TWT. The goal of this program was a TWT (double comb delay line structure) in the 94-GHz frequency range with an instantaneous bandwidth greater than 500 MHz (tunable within 1 GHz) and an output peak power greater than 200 W in the center of the band (150 W over the band) for a duty cycle of max. 10%. The basic design and main test results of the 94-GHz TWT are the content of this paper.