Defense Agency for Technology and Quality

Incremental Theory of Diffraction (ITD) is an incremental theory technique to calculate the diffracted field of a complex object in which the stationary phase condition is not well-established. In this study, the incremental diffraction contribution is ignored and the physical optics (PO) endpoint contribution is considered when calculating the bistatic radar cross-section (RCS) for the observation point corresponding to the inner region of the edge using the ITD. Accordingly, we applied shooting and bouncing rays and ITD to the trigonal prism and circular disk and verified the proposed ITD method by comparing with the results of the method of moment and the conventional ITD implemented in the IDS’s Viraf.

This paper describes the development and measurement results of a wide-band planar active phase array antenna system for an electronic warfare jamming transmitter. The system is designed as an 8×8 triangular lattice array using a 45° slant wide-band antenna. The 64-element transmission channel is composed of a wide-band gallium nitride(GaN) solid state power amplifier and a gallium arsenide(GaAs) multi-function core chip(MFC). Each GaAs MFC includes a true-time delay circuit to avoid a wide-band beam squint, a digital attenuator, and a GaAs drive amplifier to electronically steer the transmitted beam over a ±45° azimuth angle and ±25° elevation angle scan. Measurement of the transmitted beam pattern is conducted using a near-field measurement facility. The EIRP of the designed system, which is 9.8 dB more than the target EIRP performance(P), and the ±45° azimuth and ±25° elevation beam steering fulfill the desired specifications.

We have studied a combiner that can withstand high power while minimizing insertion loss in high frequency band. In particularly, because the output power that can be output per unit elements is much lower in the Ku band and above than in the low frequency band , it is necessary to combine many semiconductor elements in order to make a high power SSPA. A planar combiner such as a microstrip, as the number of elements to be combined increases, the insertion loss increases proportionally, resulting in a reduction in the overall system efficiency and an increase heating value also. The planar combiner also have some problems due to the low power handling rate. To improve these problems, we proposed a Cavity Radial Combiner. A Ku band 16-way Cavity Radial Combiner was fabricated and measured. As a result, it was tested 14dB return loss and over 94.5 % output combining efficiency in design band.

In this paper, we describe a ray-tracing method for spherical lenses and reestablish an equation for calculating the radiation pattern using a spherical lens based on previous literature by modifying the physical optics (PO) integral equation. Using this formula, we calculated the radiation pattern according to the size and point source distance of a single-medium spherical lens and a Luneburg lens. While both lenses showed that the beam width became narrower as the lens size increased, the side-lobe level decreased when the source was located on the surface of the lens in the case of the Luneburg lens and when the source was appropriately distanced from the lens surface in the case of the single-medium spherical lens. In addition, through the analysis of the focal length and the beam forming the focus when parallel rays are incident on a single-medium spherical lens, we show that a single-medium spherical lens with a refractive index of 1.4 to 1.5 can replace a complex Luneburg lens by placing the source at a distance of 0.4 λ to 0.5 λ from the lens surface.

Microstrip array antennas are used in mmWave band automotive radar applications owing to their advantages of low costs, a low profile, and ease of manufacture. Among the various structures of microstrip array antennas, microstrip comb-line array antennas have recently been used extensively, as several radiating elements can be arranged in a small space with a low loss compared to other structures. However, it is difficult to achieve the low sidelobe level(SLL) required in the mmWave band using only conventional stub-type radiating elements. In this paper, we propose a comb-line array antenna that consists of radiating elements with a constant connection width between the feeding line and the radiating element to reduce the SLL. We designed a 1×17 array antenna composed of the conventional and proposed radiating elements by applying a Taylor distribution with an SLL of −20 dB. The measured results of the prototype antenna, with a measured gain of 15.3 dBi and an SLL of −21.5 dB, satisfied the design objective.

It is essential for the near-field receiving measurement to make beam pattern and check the performance of a active phased array antenna system. Also, we could obtain compensation value for mono-pulse function through the near-field receive test, however, if the radar has many frequency channel, the test would take long time and hard effort. So it is needed that frequency channels are selected for measurement and calculates the values for other frequency channels to improve efficiency in development and manufacture. In this case, the phase variations in sum and del channels would be checked. The phase measurement includes un-linear characteristic because of wrapping effect. Generally, radars have similar path length in sum and del channel, but if a radar has a electrical length gap between sum and del channel, errors could occur by phase’s wrapping effect. In this paper, the interpolation method’s error caused by electrical length gap is checked and the effective method for frequency channel selection to avoid wrapping effect is introduced.

본 논문에서는 반도체형 전력 증폭기의 바이어스를 개선하기 위하여 순차 제어 회로와 펄스 폭 가변 회로를 적용한 X-대역 60 W 고효율 전력 증폭 모듈을 설계하였다. 순차 제어 회로는 전력 증폭 모듈을 구성하는 각 증폭단의 GaAs FET의 드레인 전원을 순차적으로 스위칭하도록 회로를 구성하였다. 드레인 바이어스 전원의 펄스 폭을 RF 입력 신호의 펄스 폭보다 넓게 하여 전력 증폭 모듈의 입력 신호가 있을 때만 스위칭 회로를 순차적으로 구동시킴으로써 전력 증폭 모듈의 열화에 따른 출력 신호의 왜곡과 효율을 향상시킬 수 있다. 60 W 전력 증폭 모듈은 고출력 GaAs FET를 이용하여 전치 증폭단, 구동 증폭단과 주전력 증폭단으로 구성하였으며, 주전력 증폭단은 전력결합기를 이용한 평형증폭기 구조로 구현하였다. 설계된 전력 증폭 모듈은 9.2~9.6 GHz에서 듀티사이클 10 %로 동작시켰을 때 50 dB의 전력 이득, 펄스 주기 1 msec, 펄스 폭 100 us, 출력 전력 60 W에서 동작함에 따라 펄스-SSPA 형태로 반도체 펄스 압축 레이더 등에 적용할 수 있다. In this paper, X-band 60 W Solid-State Power Amplifier with sequential control circuit and pulse width variation circuit for improve bias of SSPA module was designed. The sequential control circuit operate in regular sequence drain bias switching of GaAs FET. The distortion and efficiency of output signals due to SSPA nonlinear degradation is increased by making operate in regular sequence the drain bias wider than that of RF input signals pulse width if only input signal using pulsed width variation. The GaAs FETs are used for the 60 W SSPA module which is consists of 3-stage modules, pre-amplifier stage, driver-amplifier stage and main-power amplifier stage. The main power amplifier stage is implemented with the power combiner, as a balanced amplifier structure, to obtain the power greater than 60 W. The designed SSPA modules has 50 dB gain, pulse period 1 msec, pulse width 100 us, 10 % duty cycle and 60 watts output power in the frequency range of 9.2~9.6 GHz and it can be applied to solid-state pulse compression radar using pulse SSPA.

Chaffs, as radar countermeasures, are widely used to protect targets by deceiving enemy radar systems. The position, orientation, and density of the deployed chaff clouds vary depending on the frequency, launch conditions, and environmental variables. Consequently, the radar cross-section (RCS) of the chaff cloud exhibits time-varying characteristics. In prior studies, the dynamic behavior of chaff was predicted using the computational fluid dynamics-discrete element method, and a model for predicting dynamic RCS was implemented using the generalized equivalent conductor method, an approximation technique. In this study, instead of relying on numerical analysis methods, we developed a surrogate model capable of real-time prediction of the dynamic RCS by training a multilayer perceptron on the results and environmental variables obtained from existing methods. The proposed surrogate model achieved a mean square error of 0.0016 and an R2 score of 0.9307 and obtained results approximately 8.59 s faster than the existing methods.