Abstract
This paper presents an elegant yet straightforward design procedure for a compact rat-race coupler (RRC) with an extended harmonic suppression. The coupler’s conventional λ/4 transmission lines (TLs) are replaced by a specialized TL that offers significant size reduction and harmonic elimination capabilities in the proposed approach. The design procedure is verified through the theoretical, circuit, and electromagnetic (EM) analyses, showing excellent agreement among different analyses and the measured results. The circuit and EM results show that the proposed TL replicates the same frequency behaviour of the conventional one at the design frequency of 1.8 GHz while enables harmonic suppression up to the 7th harmonic and a size reduction of 74%. According to the measured results, the RRC has a fractional bandwidth of 20%, with input insertion losses of around 0.2 dB and isolation level better than 35 dB. Furthermore, the total footprint of the proposed RRC is only 31.7 mm × 15.9 mm, corresponding to 0.28 λ × 0.14 λ, where λ is the guided wavelength at 1.8 GHz.
Highlights
Microstrip rat-race couplers (RRC), known as hybrid ring couplers, are widely used microwave circuits for dividing/combining microwave input power in their four ports [1]
This paper presents an elegant yet straightforward design procedure for a compact rat-race coupler (RRC) with an extended harmonic suppression
The scattering parameters of the proposed RRC are illustrated in Fig. 10. .As shown in Fig9the scattering parame,ters of the new RRC with the proposed transmission lines (TLs) are very similar to the conventional coupler over its operating frequency band, with insertion losses and isolation better than 0.3 dB and 20 dB, respectively
Summary
Microstrip rat-race couplers (RRC), known as hybrid ring couplers, are widely used microwave circuits for dividing/combining microwave input power in their four ports [1]. Artificial TLs were used to achieve 64% footprint reduction based on planar circuit lines without external lumped components [2]. The compact branch-line coupler (BLC) application with low pass filter and open stubs was demonstrated, resulting in a significant size reduction and harmonic suppression [4]. In [9], a planar discontinuous microstrip lines are used for size reduction of the BLC, which more than 60% size reduction is achieved compared to the normal coupler This circuit does not have harmonics elimination. A highly miniaturized RRC capable of rejecting unwanted harmonics up to the 7th harmonic is presented, fabricated, and successfully tested In this design, the proposed TL comprises three sections; two high impedance lines, loaded by a low-impedance line at the middle, where the conventional λ/4 long lines are made redundant
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