We have proposed a waveguide to microstrip line transition, which perpendicularly connects one waveguide into two microstrip lines. It consists of only a waveguide and a dielectric substrate with copper foils. A backshort waveguide for typical transitions is not needed. Additionally, the transition does not require via holes on the substrate. These innovations simplify the structure and the manufacturing process. We assume that our transition and antennas are co-located on the substrate. We reduced the undesirable radiation from the transition so as not to contaminate the desirable radiation pattern. In this paper, we address output phase of our transition. Since the transition has two MSL output ports connecting to different radiation elements, the phase error between two dividing signals leads to beam shift in the radiation pattern. Unfortunately, misalignment of etching pattern between copper layers of the substrate is unavoidable. The structural asymmetry causes the phase error. In order to tolerate the misalignment, we propose to add a pair of open stubs to the transition. We show that the structure drastically stabilizes the output phase. Though the stubs create some extra radiation, we confirm that the impact is not significant. Moreover, we fabricate and measure a prototype antenna that uses the transition. In the case of with stubs, the radiation pattern is unchanged even if the misalignment is severe.

In this paper, a new formulation of equal-length three-section open stubs having two zeros located on the unit circle and one zero at z=-1 (θ=π) in the Z-plane is presented. In particular, new filter configurations consisting of equal-length two-section open stubs, cascade lines, open stubs, and three-section open stubs are employed to emulate the discrete-time filters. To examine the validity of our formulation, we realized two discrete-time Chebyshev type II low-pass filters in the form of microstrip lines. The frequency responses of these two filters are measured to validate this new formulation.

Novel microstrip lowpass filters are developed with reduced size and significantly improved stopband characteristics. After introducing quarter-wavelength open stubs, we get one or two transmission zeros in the stopband. By folding the high impedance microstrip lines, we reduce the size of the filter. Three-pole and five-pole lowpass filters are designed, and their measured frequency responses agree well with theoretical predictions.

This paper presents a dual-frequency microstrip antenna for both 2 GHz and 5 GHz for a dual-band receiver. For a simple structure and low cost design, the microstrip feed circuit is designed on the same substrate as the antenna elements. Each antenna element is directly fed by the microstrip line, and the open stubs are loaded on the feed line of 2 GHz to suppress the higher order mode resonances between 2 GHz and 5 GHz. The feed line length of each antenna is adjusted so as to change it to the open condition at the other element frequency at the feed point. In addition, we propose the antenna structure in which two antenna elements for 2 GHz are split and placed at either sides of the 5 GHz antenna to coincide with the center positions of each antenna element. We investigate the proposed antenna by calculations and measurements to show the combiner free design for the dual band antenna.