. Author manuscript; available in PMC: 2017 Oct 1.

Published in final edited form as: IEEE Trans Microw Theory Tech. 2016 Sep 12;64(10):3217–3223. doi: 10.1109/TMTT.2016.2602835

TABLE 3.

Comparison between this work and recently published microstrip couplers.

	Design method	Coupling factor (dB)	Center frequency (MHz)	Normalized bandwidth^* (%)	Directivity (dB)	Size^** (λ_g)	Tunable capability
This work at 7 T	Microstrip with lumped elements	25	298	8.8	48.2	0.05 x 0.03	Yes
This work at 9.4 T		25	400	8	43.7	0.07 x 0.04	Yes
This work at 10.5 T		25	440	7.8	41.2	0.07 x 0.05	Yes
[8]	Epsilon negative transmission line	10	2000	8.7	40	0.4 x 0.27	No
[9]	Double coupled lines with an unmatched load	20	1500	-	40	0.07 x 0.08	No
[10], (structure 1)	Microstrip with fragment structure	20	2000	45	48	0.25 x 0.1	No
[11]	Wiggly microstrip line	20	2250	20	35	0.25 x 0.04	No
[12]	Microstrip with shut inductors	20	2400	16.3	56	0.25 x 0.21	No

Normalized bandwidth = f_C/f_BW, fc: center frequency, f_BW: bandwidth of 20 dB directivity with less than 20 dB return loss

^**

Normalized coupling structure size (λ₀: the guide wavelength at the center frequency)