Presented in this paper is a conceptual design by computer simulation of a monopulse reflector antenna with dual-circularly polarized sum patterns and linearly polarized azimuth and elevation difference patterns, which can be called a semi-dual polarized antenna. The proposed antenna consists of a five-element monopulse feed and a prime-focus parabolic reflector. The novelty of the proposed antenna is a monopulse feed consisting of a dual-circularly polarized square waveguide sum channel radiator and linearly polarized rectangular waveguide azimuth and elevation difference channel radiators. The separation of dual circular polarization is realized by a septum polarizer. The difference pattern is obtained by feeding two rectangular waveguides in opposite directions using a coaxial probe. The proposed monopulse feed geometry requires only two power combiners for a monopulse comparator network while providing dual-polarized performance comparable to the full dual-polarized sum and difference channel monopulse scheme. The concept of the proposed antenna is shown in a conceptual design by computer simulation. The monopulse feed is designed first, and then combined with a parabolic reflector. The designed monopulse reflector antenna operates at 14.5–16.0 GHz, and shows excellent sum and difference pattern characteristics: 36.1–36.7 dBc sum channel directivity with 0.65 dB boresight axial ratio and 32.6–32.9 dBi difference channel directivity with 1.56–1.66° crossover angle.

The maximum reflection at an open end of a standard rectangular waveguide is about −10 dB in its operating frequency range. It is often used without matching. For critical applications, it is desirable to further reduce the reflection coefficient. In this paper, a new technique is presented for the broadband impedance matching of an open-ended rectangular waveguide. The proposed technique employs three thin capacitive matching elements placed at proper intervals via a low-loss dielectric material. The capacitance of, and distance between, the matching elements are optimized for broadband impedance matching using a simulation tool. Based on the proposed technique, two design examples are presented for the matching of a WR75 waveguide radiator. A reflection coefficient of less than −16 dB and −20 dB has been achieved over a ratio bandwidth of 2.13:1 and 1.62:1, respectively.

본 논문에서는 소형 광대역 원편파 안테나의 시뮬레이션 기반 설계 방법을 제시한다. 제안된 안테나는 상부기판, 하부기판, 4개의 역 F형 방사소자, 직렬 급전 회로망, 유전체로 둘러싸인 4개의 급전 금속봉, 2개의 단락 스터브를 포함하는 수직 기판 등으로 구성된다. 상부 기판에는 튜닝 스트립을 가지는 4개의 방사소자가 배치된다. 직렬 급전 회로망은 하부기판에 배치되어 4개의 방사소자에 동일 크기 전력과 순차적으로 90° 위상차를 가지는 신호를 공급한다. 단락형 스트립의 길이와 상부 기판과 하부기판 사이의 거리를 조정함으로써 최적 특성을 가지는 소형 광대역 원편파 안테나를 설계하였다. 설계에는 상용 시뮬레이션 툴을 이용하였다. 설계된 안테나는 70×70×14mm3의 크기, 0.865－0.928GHz에서 －10dB 이하의 반사계수, 3.2dBic 이상의 이득, 4dB 이하의 축비 특성을 가진다.

This paper presents a design of a three-branch line quadrature hybrid coupler with reduced size implemented in the microstrip line. The designed coupler is to be used in the feeding of a crossed-dipole circularly polarized antenna for receiving GNSS signals at 1.16-1.61 ㎓. The performances of the two- and three-branch line couplers are investigated first. Characteristic impedances of the three branch lines are adjusted for a better balance in coupling coefficients. To reduce the size of the three-branch line coupler, the main lines are meandered inward and outward using the optimized coupler. Meandering reduces the size of the quadrature hybrid coupler by 35.2% in one direction. The outward-meandered coupler shows slightly larger bandwidth than the inward-meandered design. The outward-meandered coupler shows magnitude and phase imbalances of 0.36 ㏈/0.7° at 1.16 ㎓, and 0.43 ㏈/0.8° at 1.61 ㎓.